Omega Owners Forum
Omega Help Area => Omega General Help => Topic started by: Albatross on 29 November 2008, 10:11:44
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I have a 3.2 which has 4 cats; a pre-cat and a main cat, and 4 O2 sensors. this is 2 of each per bank.
There is a known issue on the 3.2 and 2.6 DBW engines that codes 0420 and 0430 come up to tell you that the pre-cats are "tired", this is a measurement of the difference of the exhaust mixture from the primary O2 sensors in the series to the secondary.
Moving the secondary O2 sensors "tricks" the ECU, by cleaning the air through the main cats.
(http://farm4.static.flickr.com/3290/2915893351_a12d3f44b9.jpg)
I have done this. When I had my stainless steel "cat-back" exhaust system fitted I had them add some O2 sensor bosses behind the main cats and blanked out the original bosses with plugs. This has solved the initial problem of the 0420 and 0430 codes.
My question is this:
My car effectively no longer needs the pre-cats; would I gain much, if anything, in the way of power by replacing the front section with those from a 3.0 thereby removing the pre-cats?
My thoughts are that the pre-cats must be causing a degree of back pressure and I would have a freer flowing exhaust system without them. That is ultimately why people de-cat track cars and fit "sports cats" to their cars isn't it?
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i guess this comes down to fully understanding the exact issue with the pre cats? I have a mental picture of a collapsed pile of honeycomb sitting it the exhaust. However from what i have read this not the case i believe. More that the cleaning effect of the cat is no longer within limits...?
I also believe that if the exhaust was, in effect, blocked to any noticeable degree it would throw a code? Not confident in my understanding of all this though...
Ps. Is it poss to slide a scope down the 02 sensor boss and physically see the pre cat condition?
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Personally I don't think that the pre-cats are faulty and I don't care really. That's not this issue.
The question is: Now that I don't need them will I gain a bit of performance by removing them?
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You can remove all the cats but it may cause emission problems, also I believe there are legalities involved.
My understanding is the pre-cats do the heavy gas scrubbing to make life easier for the main cats so removing the pre-cats will shorten the life and efficiency of the main cats. I am sure I have read where people have removed the pre-cats and it made no performance gains but can't remember which vehicles this related to.
I would say the best option would be to change all the OEM cats for sports cats, not sure what the cells are in Omegas but you can get sports cats down to 100 cell. I know this was a big difference to vecs.
Does the Omega actually suffer from poor inlet and exhaust though? I know there are big gains to be had on vecs but I thout the Omegas were much better balanced and more efficient?
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You can remove all the cats but it may cause emission problems, also I believe there are legalities involved.
My understanding is the pre-cats do the heavy gas scrubbing to make life easier for the main cats so removing the pre-cats will shorten the life and efficiency of the main cats. I am sure I have read where people have removed the pre-cats and it made no performance gains but can't remember which vehicles this related to.
I would say the best option would be to change all the OEM cats for sports cats, not sure what the cells are in Omegas but you can get sports cats down to 100 cell. I know this was a big difference to vecs.
Does the Omega actually suffer from poor inlet and exhaust though? I know there are big gains to be had on vecs but I thout the Omegas were much better balanced and more efficient?
Sounds like the answer to my question is "Leave it well alone".
Thanks; I think I will do. :y
Nathan
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Wait for someone with knowledge specifically of Omegas, only had mine a couple of weeks so my knowledge isnt on these Albatross
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My understanding is the pre-cats do the heavy gas scrubbing to make life easier for the main cats so removing the pre-cats will shorten the life and efficiency of the main cats. I am sure I have read where people have removed the pre-cats and it made no performance gains but can't remember which vehicles this related to.
We're talking about replacing the front pipes with a single cat version from an earlier model, not just removing the pre-cat, so this shouldn't be an issue.
I would say the best option would be to change all the OEM cats for sports cats, not sure what the cells are in Omegas but you can get sports cats down to 100 cell. I know this was a big difference to vecs.
Me too. If you're going to play, might as well do a proper job. Having said that, I'd say the manifolds are probably the weakest link.
Kevin
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OOOOOh, manifolds. Had given up even thinking about them cos of the cost on a vec. Can you actually get them for a 6 pot omega without a mrtgage?
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OOOOOh, manifolds. Had given up even thinking about them cos of the cost on a vec. Can you actually get them for a 6 pot omega without a mrtgage?
There has been talk about them. A guy on the AutoBahnStormers site was looking into getting some made. They are certainly available for LHD cars, but I suspect would foul the steering box on a RHD car. A nice tubular manifold would make a real difference, I reckon.
Kevin
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There is someone makes them for the vec v6's, Milltech did them but I think they had to be bought through Courtenay.
I know Davey Lad at Grassmere vauxhall has done a lot of work with manifolds on the vec, (I think with a 3 litre fitted). Would have thought it easier with the omega being inline, is it the sides of the bulkhead/tunnel fouling thats the problem?
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Would upgrading / balancing the manifolds really help that much?
I'd happily let a place like long-life exhausts build me one if it were going to make that much difference.
Do you think they are the right people or is it better done by an engine tuning specialist?
I'd get the manifold and then front section (with sports cat) done at the same time.
Would they need to lift the engine to fit it in do you reckon? When they did my "cat-back" system, they built it straight onto the car.
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Would upgrading / balancing the manifolds really help that much?
I'd happily let a place like long-life exhausts build me one if it were going to make that much difference.
Do you think they are the right people or is it better done by an engine tuning specialist?
I'd get the manifold and then front section (with sports cat) done at the same time.
Would they need to lift the engine to fit it in do you reckon? When they did my "cat-back" system, they built it straight onto the car.
Any advice on this from anyone?
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I think this is a Kevin Wood, ABS, & MDTM subject
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Would a set of pre-facelift M-Reg 3.0 "mid-sections" (From the bottom of the manifolds to the rear of the main cat) fit straight onto a 3.2?
I've been offered a free pair!
Thanks
Nathan
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On the subject of manifolds I would say it needs ssomeone who knows what they are doing to get the best out of them, but anything would probably be an improvement.
The standard manifold is untuned, in that the exhaust ports for each cylinder just terminate into a common plenum with the pipe connected to one end.
The big advantage of a tubular manifold is that you can tune the lengths of the primary pipes to scavenge the cylinders more effectively and isolate the effects of adjacent cylinders. The length of these pipes depends on the engine speed at which you want them to work (there will be speeds where they are poor and speeds where they work well), and the exhaust valve timing.
Kevin
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On the subject of manifolds I would say it needs someone who knows what they are doing to get the best out of them, but anything would probably be an improvement.
The standard manifold is untuned, in that the exhaust ports for each cylinder just terminate into a common plenum with the pipe connected to one end.
The big advantage of a tubular manifold is that you can tune the lengths of the primary pipes to scavenge the cylinders more effectively and isolate the effects of adjacent cylinders. The length of these pipes depends on the engine speed at which you want them to work (there will be speeds where they are poor and speeds where they work well), and the exhaust valve timing.
Kevin
Does that mean that I could even see a drop in performance at certain engine speeds?
I don't want that, I want to retain the same smooth power curve, only higher up on the graph. I may supercharge this in the Spring when my bonus comes through so I want it to be breathing as well as it can to make the most out of the SC.
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Does that mean that I could even see a drop in performance at certain engine speeds?
I don't want that, I want to retain the same smooth power curve, only higher up on the graph. I may supercharge this in the Spring when my bonus comes through so I want it to be breathing as well as it can to make the most out of the SC.
You'll undoubtedly see an "undulation" in the torque curve as the pipes go in and out of resonance, and they are normally tuned to resonate at the maximum torque RPM for road cars. Whether at any point you'll get less torque than with the standard setup I don't know.
If you are contemplating forced induction then, although the same principles apply to getting the engine breathing well, an expensive exhaust modification might not be the most cost effective route. It would drop lower on the list of priorities, IMHO, because you'll be limited by the compression ratio and a good exhaust will just slightly reduce the boost pressure you need.
Kevin
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Does that mean that I could even see a drop in performance at certain engine speeds?
I don't want that, I want to retain the same smooth power curve, only higher up on the graph. I may supercharge this in the Spring when my bonus comes through so I want it to be breathing as well as it can to make the most out of the SC.
You'll undoubtedly see an "undulation" in the torque curve as the pipes go in and out of resonance, and they are normally tuned to resonate at the maximum torque RPM for road cars. Whether at any point you'll get less torque than with the standard setup I don't know.
If you are contemplating forced induction then, although the same principles apply to getting the engine breathing well, an expensive exhaust modification might not be the most cost effective route. It would drop lower on the list of priorities, IMHO, because you'll be limited by the compression ratio and a good exhaust will just slightly reduce the boost pressure you need.
Kevin
So are you saying that for road use (with or without an SC) that manifolds are not that good a path to go down?
What would be higher on the list of priorities?
BTW: What about this 3.0 pre-facelift mid-section question? An ABS member has offered me a set for free.
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So are you saying that for road use (with or without an SC) that manifolds are not that good a path to go down?
What would be higher on the list of priorities?
BTW: What about this 3.0 pre-facelift mid-section question? An ABS member has offered me a set for free.
I think you'd have to try hard to make things worse than the standard manifold. What I am saying is that if the exhaust is tuned there will inevitably be peaks and troughs but overall the car will be faster. You could always get a tubular manifold made up with short primaries which will flow better but not give you much in the way of resonance effects and you will retain a flat torque curve.
I don't know if the pre-facelift cats would fit or if they are more free flowing but if they're free it might be worth a try.
Kevin
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So are you saying that for road use (with or without an SC) that manifolds are not that good a path to go down?
What would be higher on the list of priorities?
BTW: What about this 3.0 pre-facelift mid-section question? An ABS member has offered me a set for free.
I think you'd have to try hard to make things worse than the standard manifold. What I am saying is that if the exhaust is tuned there will inevitably be peaks and troughs but overall the car will be faster. You could always get a tubular manifold made up with short primaries which will flow better but not give you much in the way of resonance effects and you will retain a flat torque curve.
I don't know if the pre-facelift cats would fit or if they are more free flowing but if they're free it might be worth a try.
Kevin
I've been speaking with a company who is making up a set of tubular manifolds for another ABS member. He indicated to me that the primaries would be around 10" long which is quite short. The main reason for this is the lack of space. Would that be OK and give me a more level behaviour?
What would you do rather (or as well as) manifolds in preparation for an SC if you had the opportunity?
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10" is well short of being tuned at the kind of speeds the V6 runs at, so it will just be a better flowing version of what you have, really.
The point I was making about supercharging is that, if you go that route, you will easily be able to get more volumetric efficiency out of the engine and the limit will be the standard compression ratio, assuming you're not going to lower it.
With a naturally aspirated engine you have to work at the inlet and exhaust to get more VE. With a supercharger you will be able to get as much VE as it will handle regardless of the exhaust. Having an efficient exhaust will give you a more efficient engine, of course, but won't necessarily limit power as it would with a naturally aspirated engine.
Kevin
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10" is well short of being tuned at the kind of speeds the V6 runs at, so it will just be a better flowing version of what you have, really.
The point I was making about supercharging is that, if you go that route, you will easily be able to get more volumetric efficiency out of the engine and the limit will be the standard compression ratio, assuming you're not going to lower it.
With a naturally aspirated engine you have to work at the inlet and exhaust to get more VE. With a supercharger you will be able to get as much VE as it will handle regardless of the exhaust. Having an efficient exhaust will give you a more efficient engine, of course, but won't necessarily limit power as it would with a naturally aspirated engine.
Kevin
Sorry Kevin,
I'm a bit thick on things like this and don't understand much of the above really at all.
Would I be right in thinking that in essence what you're saying is:
That the 10" tubed manifold would be OK, smoother (less undulated), but not overall as good as longer pipes? What's more it would be beneficial if naturally aspirated, but a bit of an unnecessary waste of cash if I were to fit a supercharger?
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I think the point being made is that for forced induction (supercharger or turbo or combi of both) the scavaging of exhausts gases through a specifically tuned exhaust system is lower on the list.
In essence the forced inlet charge pushes a lot of the waste gas out. Less need for the exhaust system to draw the waste gases out. Tuning equal lenghts for primary tubes so each pulse of exhaust gas can slot in turn with the next one. Then the decision/benefit of a cross pipe for V engine set ups etc
Trying to cast my mind back re long primaries v short ones v torque on motorbike builds and the benefit of primaries joing en-masse or going 4 into 2 into 1 etc
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my 2 pence, for whats its worth, i had always presumed any forced air induction, turbo or sc, would over power any effect gained by scavenging cylinders with a "tuned" exhaust. For instance a turbo exhaust takes little notice of pipe length and just takes the easiest route to where ever the turbo is positioned for convenience.
I would think you need to decide which route you want to go down. Forced induction or a free flowing exhaust.
In my experience, a longer downpipe gives a more rev happy "powerband" and basically moves the power further up the rev range,in effect gaineing on one hand and taking on the other in relation to the current curve.
I wonder if vx made the manifold that way to achieve a flat torque curve(shortest possible outlet pipes or plenum in this case), the opposite of peaky powerband delivery(longer downpipes) ? That would imply, if you want more of whats already there, a super charger would be more appropriate? If you like that sort of thing...
Alot of assumptions in there. Maybe a more experienced member can confirm?
KEVIIIIN...!
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I like my car the way it behaves, so would not want to change the characteristics of the power curve, but I would like to see if I can increase the power overall. I wouldn't want a revvy engine; hence the thought of a small supercharger rather than turbo.
I just want a more powerful car overall that's all.
To put this all into context of what else is going on at the moment here. I'm also just about to fit an LSD which will change the ratio from 3.9:1 to 3.7:1. I'll also be changing the tyre rolling radius on the tyres by going from 235x35x19 to 255x35x19 which will compensate the ratio change a small amount.
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I know the big problem with tubular manifolds on the V6 vec was getting equal length headers to fit, there just is no room. The vec is transverse though where the mig is inline, do you still have the same problems with space on them?
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If you want more power it really depends on how big your wallet is.
How much is the blower set up costing you?
How much would an over bore with race spec cams, ported and polished heads with uprated fuel pump and injectors cost compared to a blower project?
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Also depends how much of the work you're doing yourself against having it done, and whether you're after making the best of what you've got or a serious power hike.
Tuning is not something that's best done piecemeal, IMHO. Better to decide what you want to achieve and then to do what you need to do to achieve it, following one well trodden path / proven combination of mods from a single source rather than mixing and matching.
In a lot of cases, the sensible answer, IMHO, is that you shouldn't have started with a V6 Omega, but life doesn't always have to be sensible, of course. ;)
Kevin
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Also depends how much of the work you're doing yourself against having it done, and whether you're after making the best of what you've got or a serious power hike.
Tuning is not something that's best done piecemeal, IMHO. Better to decide what you want to achieve and then to do what you need to do to achieve it, following one well trodden path / proven combination of mods from a single source rather than mixing and matching.
In a lot of cases, the sensible answer, IMHO, is that you shouldn't have started with a V6 Omega, but life doesn't always have to be sensible, of course. ;)
Kevin
Kevin, very wise words; to set out the stall:
I "started with a V6 Omega" because I love it and I am not trying to build a racing car. I do not want to compromise what the best of the car is at all and simply want to make subtle modifications; I'm "after making the best of what you've I've got".
Boring out the engine is too much, perhaps even fitting a blower is too much. I'm exploring the idea of the manifolds, but am open to dissuasion.
I have done little bits and pieces and will be exploring the brakes too, but I repeat; I am not trying to build a rocket-ship out of a barn.
I suppose that the thread started in a discussion about manifolds & cats and then, perhaps understandably, it got diverted onto the "bigger picture". Now that I have clarified my "bigger picture" may I take us back to the question about manifolds?
I'd value your thoughts on manifolds with short(ish) pipes & sports cats on an otherwise unmodified 3.2 V6 Omega.
The man who makes them indicates that the gain may be as much at 20%, but you have concerned me about smoothness of the power curve.
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an interesting read, esp the bit about emissions. All manufacturers suffer with this compromise, as im sure you know, and some very nice improvements can be had by returning the motor to how Mr Vx intended, not some eco Nazi tosspot behind a desk.
http://www.courtenaysport.co.uk/index.php?act=viewDoc&docId=21
Ps i know nothing about the companys reputation, but i have seen negative remarks from other members, but i think the info is along the right lines and maybe a phone call would give the answers you need to the torque curve question, bearing in mind they will probably need the work at the moment and will most likely say what you want to hear.
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I used to have a 2.6 straight 6 Carlton which was given a chip and new head by Courtenay years ago.
I did ring them a few months back, but I must admit I was less impressed than I was previously. They did seem a bit reluctant. They said they could do more with a 3.0 than with a DBW 3.2. The main problem they said was the fact that there was less demand and therefore not enough money in investing in the research to create a remap for that engine just yet.
Having said that I do note that they now offer the following:
3.2 V6 into Vectra B
3.2 V6 Vectra B
We now offer the 3.2 V6 engine transplant into 2.5 V6 Vectra B from Ł4750. At the time of transplant we can also offer head re-working, sports camshafts, lightweight flywheel or any of our other tuning components to compliment the conversion.
I appreciate that the flywheel is useless unless I was to go to a manual conversion (which is unlikely), but the head and cam work looks interesting.
I know that many (TB) slag them off ferociously as being expensive tat, maybe that is right nowadays, but I didn't think that myself when I used them in 1995.
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an interesting read, esp the bit about emissions. All manufacturers suffer with this compromise, as im sure you know, and some very nice improvements can be had by returning the motor to how Mr Vx intended, not some eco Nazi tosspot behind a desk.
http://www.courtenaysport.co.uk/index.php?act=viewDoc&docId=21
A few pearls of wisdom amongst a load of speak that is designed to appeal to boy racers, IMHO.
You already have a very light flywheel, of course. It's just bolted to a very heavy torque converter. ::)
Exhaust / induction information is based on the FWD setup which, I imagine, has a different set of compromises to the RWD.
Water wetter, plugs, leads, cooler thermostats, air filters, etc. are a distraction. IMHO
You won't need a 4 bar pressure regulator unless you're running out of flow on the current injectors.
There's no such thing as a cam that improves torque and power unless the original cam is ridiculously mild. It will sacrifice low RPM torque for high RPM torque and hence give a higher power output, but by inserting a hole in the torque curve where the engine probably spends most of its' time on the road, especially with an autobox.
I think if I were you, wanting to improve the car but not go silly, these are the things I would try. This is based purely on what I perceive to be the weaknesses in the current engine rather than cold hard facts based on real experimentation:
Make sure the engine is running perfectly to start with.
Take off the induction system and make sure the inlet tract is smooth with no "steps" from plenum to cylinder head. Leave the internal surfaces smooth but not polished.
Fit some tubular exhaust manifolds.
Experiment with ditching the pre-cats. Perhaps a pair of 3.0 cats. If that doesn't help, perhaps weld some "sports cats" in instead and try them.
Maybe have a go at some mild porting of the heads and make sure the top end is working well (lap the valves in, etc.).
Once I've finished, find someone who can map the 3.2. IIRC, SP_3.2s car has been remapped so someone has the capability. This should include tuning on a rolling road, developing a map specific to the mods I have made not just charging 250 quid to lob in a new map.
Kevin
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an interesting read, esp the bit about emissions. All manufacturers suffer with this compromise, as im sure you know, and some very nice improvements can be had by returning the motor to how Mr Vx intended, not some eco Nazi tosspot behind a desk.
http://www.courtenaysport.co.uk/index.php?act=viewDoc&docId=21
...I think if I were you, wanting to improve the car but not go silly, these are the things I would try. This is based purely on what I perceive to be the weaknesses in the current engine rather than cold hard facts based on real experimentation:
[1]Make sure the engine is running perfectly to start with.
[2]Take off the induction system and make sure the inlet tract is smooth with no "steps" from plenum to cylinder head. Leave the internal surfaces smooth but not polished.
[3]Fit some tubular exhaust manifolds.
[4]Experiment with ditching the pre-cats. Perhaps a pair of 3.0 cats. If that doesn't help, perhaps weld some "sports cats" in instead and try them.
[5]Maybe have a go at some mild porting of the heads and make sure the top end is working well (lap the valves in, etc.).
[6]Once I've finished, find someone who can map the 3.2. IIRC, SP_3.2s car has been remapped so someone has the capability. This should include tuning on a rolling road, developing a map specific to the mods I have made not just charging 250 quid to lob in a new map.
Thanks Kevin:
:y I'm fine with points 3 & 4.
:exclamation Number 6 is pretty straightforward and I have sent a PM to Steve. I know to wait until the rest is done.
:question I'm fairly OK about point 1 (would a reassuring live reading from a Tech2 be enough?)
:question Any guidance or further detail about how to approach number 2 (this looks as though it may be within my capabilities)?
:question I guess that point 5 is where a place like Courtenay would come in; what do you think?
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OK, Having dug around a bit on ABS, chatted with Steve (SP_3.2) and considered Kevin's wise words, I think I have a plan...
Pre-test
Try the 3.0 mid sections which are free as a trial to remove the pre-cats.
Step 1:
Get these guys to make me a set of manifolds and sports cat (200 cell) mid sections. They have a proof of concept set in the making for an ABS member as we speak.
http://www.powerspeed.co.uk/
Step 2:
Then after searching around go to someone like Courtenay (or Courtenay themselves) for the head and inlet work. I'll get them to fit the manifolds whilst the heads are out.
http://www.courtenaysport.co.uk/index.php?act=viewDoc&docId=21
Step 3:
Final stage will be a quick trip to these guys to get the remapping done on a rolling road.
http://www.chippeduk.com/contact.php
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i was thinking more along the lines of asking them, or any other company with the knowledge, about the effect of various lengths of header pipe and the likely state of the power curve once the desired length was fitted...?
Ie the effects of cylinder scavenging (works better the higher the revs, afaik, and hence a peaky tune?)
with header pipes. Or a flat torque curve with the current set up(plumun manifold) i am assumeing the plenum manifold has this effect on the tune?
Personally i'd leave it be, but very interested in the results of this. Fuel prices are coming down. :-)
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Looks like a plan. Step 2 will be expensive if you get it done, as it's a heads-off job. Make sure it's going to make enough difference to justify the cost first. Sometimes a standard head will flow well enough that porting only gives a return when hot cams are being fitted.
Kevin
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Looks like a plan. Step 2 will be expensive if you get it done, as it's a heads-off job. Make sure it's going to make enough difference to justify the cost first. Sometimes a standard head will flow well enough that porting only gives a return when hot cams are being fitted.
Kevin
Kevin,
Thanks for that. Is Chris right? Would I potentially end up with a "peaky" engine? I would prefer not to change the characteristics too much only to increase overall road performance.
I might even consider cams too as part of "Step 2", but again I would value your take on this too.
Nathan
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Kevin,
Thanks for that. Is Chris right? Would I potentially end up with a "peaky" engine? I would prefer not to change the characteristics too much only to increase overall road performance.
I would say the manifolds you're considering won't have long enough primaries for length to be an issue. A quick fag packet calculation says they need to be 75cm long @ 6000 RPM. I might be wrong but that order of magnitude anyway. Significantly shorter than that and they will be operating in "non-interference". In other words, similar to the standard manifold with flat characteristics over the engine speed range but hopefully with better flow and less interaction between adjacent cylinders, so you shouldn't have to worry about them causing holes in the torque curve.
I might even consider cams too as part of "Step 2", but again I would value your take on this too.
On the whole, changing cams is a compromise unless the standard cam was extremely mild. Uprated cams typically shift the engine characteristics higher up the RPM range, so if torque is currently peaking at 3,000 RPM if might shift to 4000 RPM. If the "power band" currently starts at 2,000 RPM it might shift to 3,000 RPM. Assuming the head, valves, intake and exhaust system can flow the extra air required the torque will be at broadly the same value (it's a function of engine capacity), but because it peaks later, and power = torque x RPM you will have more power.
The extreme example is an F1 engine. 3 litre engine peaking at 19,000 RPM.. similar torque to a V6 Omega in all probability but all pushed up the the high end of the RPM range. A little more power, though :P, but has to be hept "on the boil" or there's nothing...
Driveability will suffer because the engine will be "flat" until the cams start working. With a manual box this isn't so bad, because you can drive round it. With an automatic gearbox it could get quite sluggish. I'd say given your goals uprated cams should probably not be on the list but this, along with everything I've said, is generic advice given without much knowledge of how this particular engine responds to tuning.
Kevin
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Thanks for that Kevin.
Ironically enough this ties up completely with the results of my phone calls to the 3 companies formerly mentioned above. I also ended up talking to the Technical Director at Mintek today too.
Upshot.
Advice from Mintek
Manifolds = Expensive and probably not too good an idea as they may increase the peakiness
Advice from the Exhaust company
A cross over at the mid-section would "balance" the flow.
Advice from the remapping company, UK Chipped
The standard ECU would not be able to be remapped to the extent that it would need to be to cope with the cams etc. so a new bespoke ECU would be required.
:oŁ:oŁ:oŁ:oŁ:oŁ:oŁ:oŁ:oŁ!!!!! ::) ::) ::) ::) ::)
All in all the revised, and one single completely agreed from all fronts, plan is:
- Fit new mid-sections with sports cats (Perhaps consider the cross over), but make sure that the cats are positioned correctly. If a cross over is fitted then further forward will increase torque, further back tends to increase power. The most important factor is exhaust operating temperature.
- Do not do manifolds.
- Do not do head-work and cams.
- See what can be done to smooth the inlet from the plenum and intake manifold. I can try this myself, but I may ask for advice on here.
- Get it properly remapped as SP_3.2 did at UK Chipped.
This pretty much what you originally prescribed, so utmost respect. :y
I hear what you're saying about the manifold tube lengths so I may revisit that with the mapping company and Mintek again tomorrow.
- The final item that the technical people at Mintek and Chipped UK both independently raised was the suggestion to remove the tube in the air-box so that it is flush rather than protruding 6 inches into the air-box. Both of them said that this will instantly gain about 10bhp as it was fitted like that to conform to a specific psi range for company car tax brackets.
I have seen a fibrous tube in the bottom half and a trumpet shaped affair in the top half of the air-box. I'm not sure which one they meant. I have just removed the top half of the air-box and the "trumpet" slides straight out of the exit hole. I'm just about to drive it out of town to do an errand so I'll report back in half an hour. No harm done and the "trumpet" can always slide straight back in if need be.
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Thoughts?
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sorry to stick my nose in again, when did sp32 have his car mapped? His was exactly the same bhp as mine at the rolling road day iirc it was 189 at the rear wheels both measured on the second run. Mine is bog stock with a heavy foot fitted!
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sorry to stick my nose in again, when did sp32 have his car mapped? His was exactly the same bhp as mine at the rolling road day iirc it was 189 at the rear wheels both measured on the second run. Mine is bog stock with a heavy foot fitted!
Yes Kevin is right i had my remap done about 2 years ago at a company called Chipped uk http://www.chippeduk.com/contact.php
Had a very good job done by them. They 1st put the car on a rolling road to check base BHP which was 232 they then uploaded the remap which took about 30-40mins.They then gave it a 2nd rolling road which showed 243 BHP .
The cost was about Ł250 it gave the car a better off the line pick up and better pull in D when you need it. They nice thing is that if you drive the car gently it is just the same as any other; it's when you open it up you know. As you said they are not many places that do the remaps for the 3.2...
...I would recommend these guys as they where very good; they took their time and made sure that I was happy with the change in the car and how the remap worked.
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missed the 2 year bit. They are quoting fly wheel figures. The power at the wheels will be considerably less due to the auto box, but you know all that. Fairly certain Steves and mine where the same. He did post about coil pack trouble between then and now so maybe its got some missing ponys back now.
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One thing I would say about crossover pipes is that they do not simply balance the flow but provide another resonance that can help or hinder depending on the firing order of the engine and the exact positioning. On some firing orders (flat plane V8s, IIRC, for example), they don't work at all.
Personally, I would be interested to hear what the exhaust manifolds achieve. Hopefully someone on Autobahnstormers will try them soon. I can't believe they won't improve things because the gases exit the ports and have to turn 90 degrees with the standard manifolds.
Kevin
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missed the 2 year bit. They are quoting fly wheel figures. The power at the wheels will be considerably less due to the auto box, but you know all that. Fairly certain Steves and mine where the same. He did post about coil pack trouble between then and now so maybe its got some missing ponys back now.
Good Point Chris
You are right they where the same and also about the Coil pack also had the plugs changed and replaced a unlocked injector plug which was giving a miss . All this was just after the Rolling road and it has very much helped with the missing ponys ;D ;D ;D.
Also have you hear of the trick with the air box and the feed in that Nathan came across.
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missed the 2 year bit. They are quoting fly wheel figures. The power at the wheels will be considerably less due to the auto box, but you know all that. Fairly certain Steve's and mine where the same. He did post about coil pack trouble between then and now so maybe its got some missing ponies back now.
Good Point Chris
You are right they where the same and also about the Coil pack also had the plugs changed and replaced a unlocked injector plug which was giving a miss . All this was just after the Rolling road and it has very much helped with the missing ponys ;D ;D ;D.
Also have you hear of the trick with the air box and the feed in that Nathan came across.
It's possibly the feed out "trumpet" shaped piece that I should have mentioned. See my post above and my recent new thread that I have just started in trying to find out about this thing.
I've removed it temporarily and driven the car. It may be my imagination, but it does seem a little more responsive.
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any pics?
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any pics?
Pics as requested. I think that the answer is (according to the other thread - http://www.omegaowners.com/forum/YaBB.pl?num=1229377845) that it is there to quieten the induction noise and does nothing to the performance either way. I didn't notice any difference in noise actually since I took it out though.
(http://farm4.static.flickr.com/3138/3111852340_242a425695.jpg)
(http://farm4.static.flickr.com/3102/3111852338_bfc750abd7.jpg)
(http://farm4.static.flickr.com/3246/3111852326_d0dde8b7a7.jpg)
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Had a check on my one as it,s only a few mins to remove the Air box lid not sure if it would make a diff but when i checked the inside of the box there was not the 6" of feed at the bottem of the box just flush with the box. Also had a look at the trupet on it and mine has 4 holes on each side ?.
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woo, dunno what thats for.... dja, bin it. On the other hand they must do it for a reason.
I wonder what vx call it on their system? Maybe that would give a clue, "a pipe" or some useless description probably. I wonder if its some sort of baffle so the bag pipes draw on still(er) air? Maybe...
Is the intake narrower than the exit hole? I cant picture which way round it goes.
Might have a look later.
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Yep it.s narrower on the intake ( inside the box and opens up as it comes out toward the Maf. I did not even know it was there ::).
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Vectra's had something very similar in the airbox as well. I *think* it's purpose was to cause a vacuum at the other end of the airbox to the air feed so that a wider surface area of the filter was used.
Still took it out though! ;D
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Hmm. Interesting. Looking at the pictures the bell mouthed end might be there to smooth the airflow into the intake duct, as such a shape will cause less turbulence and, if carefully designed, better flow than a simple "hole" with sharp corners.
I would wonder if it's there to provide a smooth, uniform airflow into the maf if there wasn't a 90 degree bend straight after it which will undo the good work. The fact that it has holes around the edge makes me wonder if it's been designed to cut out some resonances in the intake tract. :-/
We're at the stage where we need to borrow a rolling road to do "before and after" tests to notice any difference, I imagine.
Kevin
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I just called UK Chipped back and asked them about this. They said "remove it; it creates surge, and whilst you're at it cut the 6" fibrous spiral tube that comes into the bottom of the air-box off so that it is flush to the inside of the air-box too, that also creates surge".
So I have been out with a very sharp bread knife and done exactly that with the bottom ducting and just taken it out for a drive...
(No / flush fibrous ducting in the bottom half of air-box and no trumpet. Standard GM (very clean) air-filter)
There's a short stretch of dual carriageway near me and I know exactly how far I have gone down the road before I hit 100mph. That has just been cut by about 50 yards!
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right, out with the kitchen tools when i get home then. :-)
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Just thinking about a rolling road if we could make use of the one at Chipped up as i recall that they do this type of things for car clubs and alike.
I think when i was done there a few years ago they had some of the guys for a BMW club there testing there cars. They also haev very good equipment and know how to interpret the reading i.e auto drag as most of use of autos.
I could have a look into it if,s of any intrest.
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2.6 auto, air box mods as mentioned 0-60 7.8 seconds
I am considering some tuning, definately 3.0 cams. But even thinking of 3.2 lump.
But if I can get > 200bhp with simple mods I'll stick to 2.6
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I'm not far from them!
Bromsgrove is about 10-20 minutes from home
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I'd be up for a rolling road. It might be a useful and independent judgment before the mods.
I'll be on a rolling road when I get the final stage remap done so it will be a good comparison.
Thing is that I am already on the road to improvements now that I have the cat-back exhaust and the new air-box modifications.
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I have an AP22 data logger which is quite useful for comparisons if you can find a quiet
long straight backroad private test facility.
Kevin
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There's a short stretch of dual carriageway near me and I know exactly how far I have gone down the road before I hit 100mph. That has just been cut by about 50 yards!
Think that the Dual carriageway that i took your car out on a drive afew months ago checking out the mv6 springs and dampens. ;D ;D.
Have you noiced any change in noise :question
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There's a short stretch of dual carriageway near me and I know exactly how far I have gone down the road before I hit 100mph. That has just been cut by about 50 yards!
Think that is the Dual carriageway that I took your car out on a drive a few months ago checking out the mv6 springs and dampeners. ;D ;D.
Correct!
Have you noticed any change in noise :question
Yep!
It seems to rev more freely generally, sounds much the same at low/normal driving rev range, but give it some wellie and it sounds ferocious. Bear in mind that I have the assistance of the stainless exhaust too.
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Yep!
It seems to rev more freely generally, sounds much the same at low/normal driving rev range, but give it some wellie and it sounds ferocious. Bear in mind that I have the assistance of the stainless exhaust too.[/quote]
WoW see what you mean, took the long was home after training and it does seem to make a diff with rev and with it over 4K the sound is good :y :y.
Have a long run into work so that should be a good chance to get a feel for things.
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I'm pursuing this line of questioning elsewhere (ABS) too just to see if I can get any further insight or wisdom. I have had a bit of feedback which concerns me slightly.
can't comment on this particular setup, but I know in many cases those trumpets although look restrictive will actually help airflow at the top end of the rev range and increase power (less air turbulence as the air is directed into the AMM)
Now don't worry too much as this is specifically in reference to the top half "trumpet" and not the bottom half fibrous pipe which was what I believe the Chipped UK man was talking about and that you have already had cut flush in your air-box Steve. The trumpet may be something that we shouldn't be taking out. Noise is nice, but not at the expense of performance.
I rang Chipped UK again today for further clarification, but the technical guru there who originally advised me was "away filming with Top Gear" for the day (How cool is that?). I will call him again tomorrow to find out exactly what his take is on each of the two pipes. He did say "cut the pipe so it is flush and you'll gain horsepower, it is there as a restriction".
The trumpet piece in the top does not need "cutting" so I am guessing at this stage that he was referring to the bottom pipe only given the quote above.
I'll update tomorrow.
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Good infor
Thanks :y. As you said when i checked on my one the fibrous pipe was cut back. Car did seem to be fine at top end on the way in to work which is 90% motorway driving will keep an eye on things and check update.
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an interesting read, esp the bit about emissions. All manufacturers suffer with this compromise, as im sure you know, and some very nice improvements can be had by returning the motor to how Mr Vx intended, not some eco Nazi tosspot behind a desk.
http://www.courtenaysport.co.uk/index.php?act=viewDoc&docId=21
A few pearls of wisdom amongst a load of speak that is designed to appeal to boy racers, IMHO.
You already have a very light flywheel, of course. It's just bolted to a very heavy torque converter. ::)
Exhaust / induction information is based on the FWD setup which, I imagine, has a different set of compromises to the RWD.
Water wetter, plugs, leads, cooler thermostats, air filters, etc. are a distraction. IMHO
You won't need a 4 bar pressure regulator unless you're running out of flow on the current injectors.
There's no such thing as a cam that improves torque and power unless the original cam is ridiculously mild. It will sacrifice low RPM torque for high RPM torque and hence give a higher power output, but by inserting a hole in the torque curve where the engine probably spends most of its' time on the road, especially with an autobox.
I think if I were you, wanting to improve the car but not go silly, these are the things I would try. This is based purely on what I perceive to be the weaknesses in the current engine rather than cold hard facts based on real experimentation:
Make sure the engine is running perfectly to start with.
Take off the induction system and make sure the inlet tract is smooth with no "steps" from plenum to cylinder head. Leave the internal surfaces smooth but not polished.
Fit some tubular exhaust manifolds.
Experiment with ditching the pre-cats. Perhaps a pair of 3.0 cats. If that doesn't help, perhaps weld some "sports cats" in instead and try them.
Maybe have a go at some mild porting of the heads and make sure the top end is working well (lap the valves in, etc.).
Once I've finished, find someone who can map the 3.2. IIRC, SP_3.2s car has been remapped so someone has the capability. This should include tuning on a rolling road, developing a map specific to the mods I have made not just charging 250 quid to lob in a new map.
Kevin
i think the point behind a cooler running thermostat is to reduce overheating rather than a "performance" increase lol
hence why i'v bought one for when i try and melt some cylinders with a turbo :P
anyway... nathan, as regards the manifolds and intake/exhaust- if your running it naturally aspirated then yes you will need to tune the cam profiles, intake manifolds and exhausts to get the best airflow and get the most power but... that is usually expensive if you want it done properly
or you could play "lets crash the toy cars into eachother to see what happens" but with real cars and put a turbo/superharger on... which will mean that the exhaust and intake manifolds dont really have to flow very well as the blower will just force the air flow through regardless and it's just a case of how much boost you want (without going daft)
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I don't want to "go daft"; just mildly enhance methinks
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could use a s/charger or turbo to get a couple of psi boost which should run fine without remapping or anything
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could use a s/charger or turbo to get a couple of psi boost which should run fine without remapping or anything
I think that this was all covered off earlier in the thread TBH
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sorry to repeat things nathan, from what i got told the v6's are ok upto 6psi-no more, without any mapping just for reference :y
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What you've been told from where?
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Hi Nathan, interesting reading this thread I have a 2.5 manual saloon which i have played around with
1. lightened flywheel
2. reprofilled cams
3. ported heads
4. remapped chip
5. stainless cat back exhaust (sports cats)
6. modified viper ram air induction kit with relocated cold air feed
7. rollin road tuned
192 bhp and 187 lbs/foot, quick of the line pdq once on the move
Ive gone as far as I can go with out manifolds and/or turbo/superchargin then again there is nitrous.
All the above has had a a maked affect on performance not all of it good hence why i thought of turbo or superchargin, I have spoken to a exhaust maker with reguards to manifolds though the cost of these are beyond my budget at the moment.
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Interesting thread. I still would prefer to put a proper engine in mine one day - V8 :).
Just one comment...
To put this all into context of what else is going on at the moment here. I'm also just about to fit an LSD which will change the ratio from 3.9:1 to 3.7:1. I'll also be changing the tyre rolling radius on the tyres by going from 235x35x19 to 255x35x19 which will compensate the ratio change a small amount.
Changing from a 3.9 to a 3.7 diff will give you taller gearing, i.e. slower acceleration/higher theoretical top speed. Going to larger radius tyres will add to that effect, not cancel it out.
Liam
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Hi Nathan, interesting reading this thread I have a 2.5 manual saloon which i have played around with
1. lightened flywheel
2. reprofilled cams
3. ported heads
4. remapped chip
5. stainless cat back exhaust (sports cats)
6. modified viper ram air induction kit with relocated cold air feed
7. rollin road tuned
192 bhp and 187 lbs/foot, quick of the line pdq once on the move
Ive gone as far as I can go with out manifolds and/or turbo/supercharging then again there is nitrous.
All the above has had a a marked affect on performance not all of it good hence why i thought of turbo or supercharging, I have spoken to a exhaust maker with regards to manifolds though the cost of these are beyond my budget at the moment.
So what's been good and what's not?
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"235x35x19 to 255x35x19"
there's no difference in radius, only in tyre width
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main bad points are PRICE for what i have done to the car i could have got another omega fuel economy or lack of it and 5000 service intervals,and exhaust sound while cruisin can be boy racerish and boomy.
GOOD POINTS
quick very quick when floored very tractable the ideal sleeper car looks normal but capable of very swift travel the power to upstage bmws and mercs
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What you've been told from where?
basically (i think they're a member on vvoc) i was talking to somebody on migweb/mvoc and they said how they'd turbo'd the vectra 2.5 but said to only run it upto 6psi, they said it'd run but it really wanted mapping for the boost at 6psi and then anything over that it needs fuel management and spacer plates etc
so reading between the lines i'd go for 4psi max with nothing done and then better safe than sorry
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What you've been told from where?
basically (i think they're a member on vvoc) i was talking to somebody on migweb/mvoc and they said how they'd turbo'd the vectra 2.5 but said to only run it upto 6psi, they said it'd run but it really wanted mapping for the boost at 6psi and then anything over that it needs fuel management and spacer plates etc
so reading between the lines i'd go for 4psi max with nothing done and then better safe than sorry
for the hassle of fitting a turbo only to run at 4psi its not worth it will mabye get you 15/20 bhp ! :o :o
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What you've been told from where?
basically (i think they're a member on vvoc) i was talking to somebody on migweb/mvoc and they said how they'd turbo'd the vectra 2.5 but said to only run it upto 6psi, they said it'd run but it really wanted mapping for the boost at 6psi and then anything over that it needs fuel management and spacer plates etc
so reading between the lines i'd go for 4psi max with nothing done and then better safe than sorry
for the hassle of fitting a turbo only to run at 4psi its not worth it will mabye get you 15/20 bhp ! :o :o
lol...yes- which is why im on about going the whole hog (spacer plates,fuel management, audi intercooler and all that rubbish)
then i can run more boost ;)
anyway from what iv seen of a 3.0 saab turbo it would take it to around 320nm of torque...at low boost, which is worth something!
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"235x35x19 to 255x35x19"
there's no difference in radius, only in tyre width
Not true
The middle "35" bit is a % of the width of the tyre. i.e the 35 = 35% of the width expressed in mm
Therefore the "35" on a 235 = 82.25mm tyre wall height, whilst "35" on a 255 = 89.25mm tyre wall height.
That is 7mm difference in "height" (rolling radius) or 14mm difference in overall height of the tyre.
Multiply that by Pi ([ch960]) which equals "roughly" 3.14159265358979323846264338327950288419716939937510 (it is an irrational number so has no finitely exact value) and you'll end up with a rolling radius difference of 43.982297150257105338477007365906mm.
To back this up; if you look on here:...
http://www.club80-90syncro.co.uk/Syncro_website/TechnicalPages/TRC%20calculator.htm
...you'll see that the rolling radii are 1974mm and 2016mm respectively for the two tyre's sizes that you claim are the same which is a difference of 42mm on the rolling circumference and 7mm on the dynamic rolling radius.
This is obviously not exact as all sorts of things such as variances in manufacturers specifications come into play, but in principle you're wrong on this one mate.
;)
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What you've been told from where?
basically (i think they're a member on vvoc) i was talking to somebody on migweb/mvoc and they said how they'd turbo'd the vectra 2.5 but said to only run it upto 6psi, they said it'd run but it really wanted mapping for the boost at 6psi and then anything over that it needs fuel management and spacer plates etc
so reading between the lines i'd go for 4psi max with nothing done and then better safe than sorry
for the hassle of fitting a turbo only to run at 4psi its not worth it will mabye get you 15/20 bhp ! :o :o
Not worth the hassle if you can get that with a decent exhaust system and a professional rolling road remap. I reckon you'd get better fuel economy, responsiveness and engine longevity from the exhaust / remap route rather than a blower too.
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sorry about those tyre sizes nathan, was having a blonde moment and forgot it was percentage of the width (duuuh)
anyway... if your still wanting more power after a remap and exhaust then where else can you go :P?
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sorry about those tyre sizes nathan, was having a blonde moment and forgot it was percentage of the width (duuuh)
anyway... if your still wanting more power after a remap and exhaust then where else can you go :P?
Monaro VXR ;D
That's definitely on my list. I just need to check my bonus this year.
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lol ordinary monaro is fast enough!
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much as i like the Monaro, fairly sure i would keep the Mig and the cash in the bank. But then i guess that depends on the size of ones bonus! :o
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id rather have a commodore :P (the 98 vt version though)
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...or maybe the vx/hsv version
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To think I had an Australian mate at school who went back home and got a job for HSV. Last I heard he was playing with their version of the dodge viper. Should have kept in touch with him. :'(
Kevin
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To think I had an Australian mate at school who went back home and got a job for HSV. Last I heard he was playing with their version of the dodge viper. Should have kept in touch with him. :'(
Kevin
Caw, that is a shame, would have been interesting.
Just a thought over the last couple of days, yes it took that long, where does economy fit in with all this omega state of tune business? Bear with me i can hear terribly sorry old boy, I am a little tireding.
More air flow will mean more fuel to balance the mixture, but less pedal for the same amount of go if you have the restraint(ish?), depending on the tune presumably?
With ref to the manifolds, as Kevin says, they must be restrictive in some way with a right angle exit, but what is the effect of that restriction? does that give the flat torque curve or is it over square piston "width/stroke" dimensions that give this smooth effect if thats what the omega has, or simply is the result of a big low reving v6? A result of a combination of all of those things to meet a design brief of a smooth executive, possibly chauffer driven saloon perhaps? But add in fuel economy, which lets face it is fairly poor, at this point my uneducated brain is telling me something is a bit miss matched. A high reving, peaky, race tuned, lets assume v6 to keep things simple for comparison, would presumeably be the least economical tune. The opposite of that tune would be whats in the 3.2 now, for comfort for instance, yet it still drinks the stuff like its got a hole in the fuel tank by comparison to most other similar cars . Why? V6s are thirsty, why would it be over other engine configs, and why esp. is the omega more thirsty than most V6s in my limited experience at least? I dont have figures of v engine economy with the omega dead bottom of the table but something seems disproportionate to me. Weight of the mig dont help but even so...
If thats fair comment? And if so whats the missmatch? Manifolds? Presumably these are compromised by cost/ease of manufacture and could give a more "efficient" engine over all if that compromise was removed? Depends on the design i suppose, which, i think, brings me full circle right back to where we started. Anyone?
Alot of assumptions in there again so go steady...
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When it comes to fuel economy think a little bit broader than the engine. How much weight is it shifting? Through what transmission?
You need a certain amount of energy to shift 1.7 tonnes off the lights and that comes from fuel. Having a more powerful engine might mean it's slightly less efficient at turning petrol into motive power under light load, but the majority of the fuel consumption is due to work done, not engine size/tune, etc. That's why there isn't a vast difference in fuel consumption between all the petrol engine options. They are all shifting the same weight and the efficiency differences are only give or take a few MPG. A v6 will have higher frictional losses than a 4 pot, for example, but it can generate the same power at lower RPM, so the effects tend to cancel to a degree.
I wouldn't say the Omega is any worse than most equivalent cars, but obviously lighter cars will be less thirsty, and being correct wheel drive does carry a weight penalty over FWD.
Now, if you tune the engine, you will change its' characteristics. If it has to rev higher to make more power, there are obviously greater losses due to friction internally. If it's breathing through a turbo that has lossess associated with it, so extra power does come at a price.
Simply improving the standard induction and exhaust systems so that they flow optimally shouldn't make any difference to fuel consumption IMO. It's when you get into changing cams and forced induction that it will.
The one big factor that you've missed out of the manufacturer's balancing act is cost. It's much cheaper to cast cr@p exhaust manifolds than it is to fabricate nice tubular ones. EDIT: sorry, you didn't miss it, on second reading. :-[ but I think it is the most significant.
Kevin
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the omega was built the way legislation allowed for at the time that is a compromise between emissions v consumption and power v weight.
the v6 engine was indeed tuned for a fat and flat torque curve as it is torque that gets a vehicle moving not bhp. 4 pot petrol omegas use more or less fuel as the six pot cos their power is devloped higher up the rev range. 2.0 16 valve is 100kw@5600 and 185nm @ 4000 V 2.5 v6 24 valve 125kw @ 6000 and 227nm @ 3200 3.0 v6 24 valve 155 nm @ 6200 and 270nm @ 3600.
although the outputs stated give the maximum output at the revs stated you need to understand that the 2.0 16 torque curve is steep very little torque below 2000 revs then 110nm rising to 185nm at 4000 back down to100nm by 5000 revs. the v6s by comparison deliver over 180nm from 1600 revs to 5200revs with the peak coming in in the middle of the range.
I shall concentrate on the v6 now. You can gain a higher torque figure for a longer rev range by altering the cam phasing without making the power delivery peaky,by fitting reprofiled cams that are only altered from standard by 8 degrees this still gives a fat and flat torque curve however instead of 180nm between 1600 and 5200 you get 195 nm. not alot more i grant you but enough to lower in gear acceleration by about 1.1 seconds over standard.
I have done quite abit to my 2.5 manual the only thing left to do is the exhaust side of the combustion cycle. I fitted a cold air feed air filter to reduce the temp of the air entring the engine making the air denser therefore giving a better responce when mixed with fuel and fed in to the engine. i have reprofiled cams to alter the valve times to allow better combustion had head work done on the valves size and shape a remap done while the car was being driven to get rid of flat spots sports cats and stainless cat back exhuast to get the spent gases out quicker lightened flywheel to aid throttle responce.
While i can drive around on a light throttle in town and still get 20 to 22.5 mpg when you start puttin your foot down that dips to 15 to 17 mpg yet while crusing to liverpool at a steady 80 i get 31 or 32 mpg.
I will admit that the cost of the modifactions i have done are not cheap or practical but to me they are worth every penny ive spent.
As for tubular manifolds and/or forced induction the cast iron exhaust manifolds fitted to all mass produced cars are tuned for economy and built for a low price they will always be restrictive it is weather you can afford to or want to change them from standard however i have in the past fitted tubular manifolds to various vauxhall carltons and senators with 3.0 engines and they have only improved performance and sound with no negitive side affects.
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the omega was built the way legislation allowed for at the time that is a compromise between emissions v consumption and power v weight.
the v6 engine was indeed tuned for a fat and flat torque curve as it is torque that gets a vehicle moving not bhp. 4 pot petrol omegas use more or less fuel as the six pot cos their power is devloped higher up the rev range. 2.0 16 valve is 100kw@5600 and 185nm @ 4000 V 2.5 v6 24 valve 125kw @ 6000 and 227nm @ 3200 3.0 v6 24 valve 155 nm @ 6200 and 270nm @ 3600.
although the outputs stated give the maximum output at the revs stated you need to understand that the 2.0 16 torque curve is steep very little torque below 2000 revs then 110nm rising to 185nm at 4000 back down to100nm by 5000 revs. the v6s by comparison deliver over 180nm from 1600 revs to 5200revs with the peak coming in in the middle of the range.
I shall concentrate on the v6 now. You can gain a higher torque figure for a longer rev range by altering the cam phasing without making the power delivery peaky,by fitting reprofiled cams that are only altered from standard by 8 degrees this still gives a fat and flat torque curve however instead of 180nm between 1600 and 5200 you get 195 nm. not alot more i grant you but enough to lower in gear acceleration by about 1.1 seconds over standard.
I have done quite abit to my 2.5 manual the only thing left to do is the exhaust side of the combustion cycle. I fitted a cold air feed air filter to reduce the temp of the air entring the engine making the air denser therefore giving a better responce when mixed with fuel and fed in to the engine. i have reprofiled cams to alter the valve times to allow better combustion had head work done on the valves size and shape a remap done while the car was being driven to get rid of flat spots sports cats and stainless cat back exhuast to get the spent gases out quicker lightened flywheel to aid throttle responce.
While i can drive around on a light throttle in town and still get 20 to 22.5 mpg when you start puttin your foot down that dips to 15 to 17 mpg yet while crusing to liverpool at a steady 80 i get 31 or 32 mpg.
I will admit that the cost of the modifactions i have done are not cheap or practical but to me they are worth every penny ive spent.
As for tubular manifolds and/or forced induction the cast iron exhaust manifolds fitted to all mass produced cars are tuned for economy and built for a low price they will always be restrictive it is weather you can afford to or want to change them from standard however i have in the past fitted tubular manifolds to various vauxhall carltons and senators with 3.0 engines and they have only improved performance and sound with no negitive side affects.
hi Dan, interesting stuff,
did you buy these manifolds off the shelf, or have them made? and if, made to what spec.?
cheers
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Hi Chris
the manifolds for the carlton/senator where sold by a german tuning company and indeed where "off the shelf" they did do a bespoke manifold/exhaust system for the senator whoever that ment going to germany for 3 days.
The last senator i had back in1992 was a 24 valve 3.0 manual which i tuned to the limit, ported and polished head 285 piper cams veneir pullies alpha weber ignition/injection manifolds from germany exhaust from ashley stainless in leeds rollin road set-up net result was 320 bhp up from 204 and 296 lbs/foot t up from 199
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I'm pursuing this line of questioning elsewhere (ABS) too just to see if I can get any further insight or wisdom. I have had a bit of feedback which concerns me slightly.
can't comment on this particular setup, but I know in many cases those trumpets although look restrictive will actually help airflow at the top end of the rev range and increase power (less air turbulence as the air is directed into the AMM)
Now don't worry too much as this is specifically in reference to the top half "trumpet" and not the bottom half fibrous pipe which was what I believe the Chipped UK man was talking about and that you have already had cut flush in your air-box Steve. The trumpet may be something that we shouldn't be taking out. Noise is nice, but not at the expense of performance.
I rang Chipped UK again today for further clarification, but the technical guru there who originally advised me was "away filming with Top Gear" for the day (How cool is that?). I will call him again tomorrow to find out exactly what his take is on each of the two pipes. He did say "cut the pipe so it is flush and you'll gain horsepower, it is there as a restriction".
The trumpet piece in the top does not need "cutting" so I am guessing at this stage that he was referring to the bottom pipe only given the quote above.
I'll update tomorrow.
OK, an update:
Cut the fibrous pipe out as this has been verified by over 5 discrete sources as being added specifically to restrict air-flow and keep the 3.2 within a certain power tax bracket for company car use. Cutting it flush does increase performance and not noise.
Do not remove the trumpet shaped affair in the top of the air-box as this is needed. Removing it is actually detrimental and caused my car symptoms which reconcile with what I read on a German forum. With the trumpet removed my car would occasionally stall from a warm start as the idle would drop too low.
Will be checking out exhaust mid sections with sports cats now and the benefits (or not) of a balanced cross over and if this is good where should it go for the best balance of torque gains.
Tubular manifolds will be following that shortly, but the jury is out on that one as to whether it will be of much benefit.
I am going to a fully qualified Vx Omega tuning specialist in January (with Dan ^^) who tuned all of the Nottinghamshire plod Omegas who will give me some more insight.
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you'll have to let us know what modifications there are and what sort of price we're looking at if neither you or him mind ;)