Omega Owners Forum
Chat Area => General Car Chat => Topic started by: feeutfo on 03 August 2011, 11:03:43
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I want to lower the gearing on my 3.2 auto.
Why? It has 18"wheels with 245 40 18 tyres which may or may not be oversized, not sure. But it also has an LPG tank in the boot which adds a little weight. So it feels a fraction sluggish. Only a fraction mind, it's a seat of the pants thing so I may well be imagining that bit or I have just got used to it....
But more than that, as said before, as stock it's geared for top speed which I'll never see round here, too much traffic, and it's a free tune up so to speak. Better acceleration with out altering or stressing the engine tune as stock.
As some know I have already swapped the stock dif thinking it was lower geared, but it's the same as the stock one. This was intended to be an experiment to decide if the gearing was suitable for a rebuilt LSD to that gearing, but as it's the same we're back to square one.
So, anyone know what gearing resides in a plod spec auto dif...? Needs to be lower than 4.2. And should give 3.500 rpm at 80 mph as opposed to 3000 rpm at 81 or whatever it is as standard.
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Here are the standard ratios:
(http://images.omegaowners.com/images/techinfo/omega_gearratios/gearratiosbv9.jpg)
According to that your car should have had a 3.9 diff from the factory. I'm sure we compared the two on the bench at Aldershot and the ratios were stamped on the crownwheel, and different. Unless we put the old one... No. I'm not even going to say it. :-X
IIRC, plod LSDs were 3.9 but the manual cars would ordinarily have had 3.7 diffs, hence a manual plod car would be lower geared than a manual retail car (back in the pre-3.2 days when manuals were available).
A glance at that chart shows me that if your car originally had a 3.9 the upgrade would be to a 4.22 and there are plenty of potential donors (any 2.6, or a 2.2 auto).
I think we need to know what you've currently got, for definite, though. To be sure, we need an accurate RPM at a given accurate speed (from a GPS) and a WRPM figure for the tyres you have on it.
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I have suspected for some time that there are two different ratios of plod spec (e.g. LSD) diff.
I am pretty sure my mini facelfit 3.0 estate auto have a 3.9:1 ratio diff which I know was LSD (as this is what was used for the oil change guide!)
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I want to lower the gearing on my 3.2 auto.
Why? It has 18"wheels with 245 40 18 tyres which may or may not be oversized, not sure. But it also has an LPG tank in the boot which adds a little weight. So it feels a fraction sluggish. Only a fraction mind, it's a seat of the pants thing so I may well be imagining that bit or I have just got used to it....
But more than that, as said before, as stock it's geared for top speed which I'll never see round here, too much traffic, and it's a free tune up so to speak. Better acceleration with out altering or stressing the engine tune as stock.
As some know I have already swapped the stock dif thinking it was lower geared, but it's the same as the stock one. This was intended to be an experiment to decide if the gearing was suitable for a rebuilt LSD to that gearing, but as it's the same we're back to square one.
So, anyone know what gearing resides in a plod spec auto dif...? Needs to be lower than 4.2. And should give 3.500 rpm at 80 mph as opposed to 3000 rpm at 81 or whatever it is as standard.
its that diff what you got of me last year??
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Ah yes, memory fails again. 4.2 was the target spec. Not the stock spec of 3.9.
So if that is a 4.2 installed currently it's not low enough. Or it's brought the current gearing back to standard with those wheels...?
So yes, need to evaluate what's currently fitted correctly.
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I want to lower the gearing on my 3.2 auto.
Why? It has 18"wheels with 245 40 18 tyres which may or may not be oversized, not sure. But it also has an LPG tank in the boot which adds a little weight. So it feels a fraction sluggish. Only a fraction mind, it's a seat of the pants thing so I may well be imagining that bit or I have just got used to it....
But more than that, as said before, as stock it's geared for top speed which I'll never see round here, too much traffic, and it's a free tune up so to speak. Better acceleration with out altering or stressing the engine tune as stock.
As some know I have already swapped the stock dif thinking it was lower geared, but it's the same as the stock one. This was intended to be an experiment to decide if the gearing was suitable for a rebuilt LSD to that gearing, but as it's the same we're back to square one.
So, anyone know what gearing resides in a plod spec auto dif...? Needs to be lower than 4.2. And should give 3.500 rpm at 80 mph as opposed to 3000 rpm at 81 or whatever it is as standard.
its that diff what you got of me last year??
It is indeed. Thank you Serek.
Edit, forgot the thumbs up smiley :y
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Continental SC3 in 235/45/17 has a WRPM figure of 821.
At 245/40/18 it's 811. Not really a significant difference.
At 80MPH with the 235/45/17 Wheel RPM is 821*(80/60) = 1095
Multiply by diff ratio 1095*3.90 = 4269 at the propshaft
Multiply by gearbox ratio 4269*.72 = 3074 at the engine.
With the new tyre size 3074 * (811/821) = 3036 RPM
With the 4.22 diff 3036 * (4.22/3.90) = 3285 RPM
So, bearing in mind that the speedo will be over-reading, if you are seeing 3,000 RPM at an indicated 80 you might well have the 4.22. I know mine shows almost 85 at 3,000 RPM.
EDIT: Hmm. That might not be right, actually. Need to have a look on the way home. :-[
Either way, at a true 80MPH you should be doing 3285.
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formula is.....
mph per 1000 revs = 60000 divided by ( wrpm x final drive ratio x gear ratio )
your car has a 1:1 ratio in 3rd gear, so that's the one to measure in, but here's the output anyhow....
821 wrpm is spot on ( well, very close to the "standard of 817 )
so you have 18.74 mph per 1000 revs in 3rd and 16.02 in 4th if you have a 3.9
or 17.31 mph per 1000 revs in 3rd and 24.04 in 4th if you have a 4.22
the LSD I have for you is 4.22.
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Continental SC3 in 235/45/17 has a WRPM figure of 821.
At 245/40/18 it's 811. Not really a significant difference.
At 80MPH with the 235/45/17 Wheel RPM is 821*(80/60) = 1095
Multiply by diff ratio 1095*3.90 = 4269 at the propshaft
Multiply by gearbox ratio 4269*.72 = 3074 at the engine.
With the new tyre size 3074 * (811/821) = 3036 RPM
With the 4.22 diff 3036 * (4.22/3.90) = 3285 RPM
So, bearing in mind that the speedo will be over-reading, if you are seeing 3,000 RPM at an indicated 80 you might well have the 4.22. I know mine shows almost 85 at 3,000 RPM.
EDIT: Hmm. That might not be right, actually. Need to have a look on the way home. :-[
Either way, at a true 80MPH you should be doing 3285.
Oh ok. So "my seat of the pants" is quite accurate. And given I haven't really understood most of those calculations, what does that tell us... ;D
I'll set my idiot nav on the way home and see what rpm we have at a gps indicated 80mph in top and third gear. See if we arrive at the same figure. :y
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formula is.....
mph per 1000 revs = 60000 divided by ( wrpm x final drive ratio x gear ratio )
your car has a 1:1 ratio in 3rd gear, so that's the one to measure in, but here's the output anyhow....
821 wrpm is spot on ( well, very close to the "standard of 817 )
so you have 18.74 mph per 1000 revs in 3rd and 16.02 in 4th if you have a 3.9
or 17.31 mph per 1000 revs in 3rd and 24.04 in 4th if you have a 4.22
the LSD I have for you is 4.22.
Ooh ooh LSD :) is there scope to lower the gearing if needed :-[
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Having found a nice roundabout out Brackley way last weekend I can see a fitting end coming up for those Linglongs my wheels came with. ;D
Anyone got any Falkens they want to kill. :)
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Right. Been out and tried it. True 80MPH = 84 MPH on the speedo and a shade over 3000 RPM.
Oh ok. So "my seat of the pants" is quite accurate. And given I haven't really understood most of those calculations, what does that tell us...
If yours indicates 84MPH at just over 3,000 RPM you have the same diff as me (tyres make no odds to the speedo reading).
If yours indicates 84 MPH at 3285 RPM you have a 4.22 diff.
so you have 18.74 mph per 1000 revs in 3rd and 16.02 in 4th if you have a 3.9
If you meant 26 then I agree. ;)
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Just got home. True 80mph on nav (flicking between 79 and 80 over a good 10 miles)with cruise set shows 3250 rpm. Press sport mode or engage 3rd gives 4550.
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Sounds like a 4.22 diff to me. :y
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Ok thanks Kev. :y
So that proves that, which is good. But it also proves plod spec is lower geared/higher rpm at 80.
Keeping things simple for a second :-[ an idicated 80 in an auto plod spec car gives 3500. An indicated 80 in mine gives lass than that. Needs another 250 rpm at 80. As I understand it.
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Not driven it for a few weeks ::), but iirc 80 in mine is a touch under 3000rpm. Diff is def 3.7, but not sure if lsd or not. Car is quite reluctant to light up the back end. :-/
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Keeping things simple for a second :-[ an idicated 80 in an auto plod spec car gives 3500. An indicated 80 in mine gives lass than that. Needs another 250 rpm at 80. As I understand it.
Definitely Auto? 'cos the manual box would give you slightly lower gearing again. Otherwise, we're looking for a diff ratio > 4.22:1. Might have been a plod special, I suppose. :-/
What tyres were on this car?
.. and do you know the speedo was reading correctly / with known error?
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there are no higher diffs than 4.22.
a 4.22 will give you 51.9 mph in 3rd at 3000 revs
a 4.22 will give you 72.1 mph in 4th at 3000 revs
Chris - YHM !
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Keeping things simple for a second :-[ an idicated 80 in an auto plod spec car gives 3500. An indicated 80 in mine gives lass than that. Needs another 250 rpm at 80. As I understand it.
Definitely Auto? 'cos the manual box would give you slightly lower gearing again. Otherwise, we're looking for a diff ratio > 4.22:1. Might have been a plod special, I suppose. :-/
What tyres were on this car?
.. and do you know the speedo was reading correctly / with known error?
Def plod auto, I changed the cam belt on it, and the hbv. It's 04 registered and was ordered but never actually purchased by the police hence the private owner had it from new. He said a dealer bought them all from vx and where all lined up in a row as a job lot.
Tyres where stock size 235 45 17 Dunlop sp 9000 with stock 03 wheels. I drove it several times after cam belt fitting, and also after he lpg'd the car with a 100 litre tank in the boot to see if it lagged as my old car did on gas. It didn't.
I do remember commenting his steering box was suitably tight. It was lower than stock mv6 and firmer. Suspension was boge.
Re speedo can't remember if it was calibrated or not. If it was that might explain it...?
Last I heard the car was up for sale. A while ago now though.
Owner has since bought a Black Elite. He doesn't like the suspension. ;D
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He just replied to my text. Speedo is calibrated with confirmation sticker on the dial.
Also the car is currently on auto trader. ;)
White 3.2 saloon. :-X
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Remember there are several potential sources of error in what you have observed. Speedo reading is one. If the car was a special order it might have ended up with a dash configured for different WRPM than the wheels that ended up bolted to it. It might have had a calibrated speedo which was never properly configured, or been destined to get a calibrated speedo so they just slapped a standard dash in before sale.
Then there's the tachometer. It's a relatively crude gauge. Not impossible that it was a couple of hundred RPM out.
Owner has since bought a Black Elite. He doesn't like the suspension.
Here we go again.. (http://dl.dropbox.com/u/26795734/Smilies/bangshead.gif)
;D
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He just replied to my text. Speedo is calibrated with confirmation sticker on the dial.
Of course, calibrated doesn't mean accurate, it means verified to be reading within given tolerances (unknown to us).
I think it's highly unlikely that a bespoke diff would have been made for this car, so the difference must be in calibration of the dash. :-/
We have a new FAQ on this subject thanks to some rather useful graphs contributed by 2woody:
http://www.omegaowners.com/forum/YaBB.pl?num=1312469626
Kevin
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He just replied to my text. Speedo is calibrated with confirmation sticker on the dial.
Of course, calibrated doesn't mean accurate, it means verified to be reading within given tolerances (unknown to us).
I think it's highly unlikely that a bespoke diff would have been made for this car, so the difference must be in calibration of the dash. :-/
We have a new FAQ on this subject thanks to some rather useful graphs contributed by 2woody:
http://www.omegaowners.com/forum/YaBB.pl?num=1312469626
Kevin
Yes thanks 2woody. :y
So with my wheel size in mind, some of the effect of the 4.2 will have bern lost...? If so, how much? Is it quantifiable...? :-/
With the LPG tank as well hopefully should be at least back to square one or better.
Also wonder when 2woody is down again. Springs for dif seem a fair swap... :-X ;D
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And another q, possibly a stupid one, but is there anything to gain put of setting the wheel size by tech2?
Will that bring the speedo in to line with actual speed?
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I'm around next week as it happens...
the Omega size of tyre gives 817 wrpm, so your 821 gives only a 0.4% error. not worth correcting
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Wheel size was the difference between 3074 and 3036 RPM. Not significant at all.
Configuration via Tech 2 is only to adjust for different Omega wheel sizes, you can't tweak it freely. It might be that one of the other sizes is a better match but I doubt it, given that your WRPM has changed by only just over 1%. There's probably more variation between different brands of tyre.
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Ok thanks Kev. :y
So that proves that, which is good. But it also proves plod spec is lower geared/higher rpm at 80.
Keeping things simple for a second :-[ an idicated 80 in an auto plod spec car gives 3500. An indicated 80 in mine gives lass than that. Needs another 250 rpm at 80. As I understand it.
Calibrated speedo may be the culprit
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I'm around next week as it happens...
It is about time for someone to say "Curry"?
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"CURRY" ....? ;D
Or whatever.
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"CURRY" ....? ;D
Thought so. ::)
Or whatever.
You can experiment if you like. I'll stick to what I know, thanks. ;)
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"CURRY" ....? ;D
Thought so. ::)
Or whatever.
You can experiment if you like. I'll stick to what I know, thanks. ;)
;D well apparently not "everyone" likes curry. :-/ strange concept I know.... :y
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"CURRY" ....? ;D
Thought so. ::)
Or whatever.
You can experiment if you like. I'll stick to what I know, thanks. ;)
;D well apparently not "everyone" likes curry. :-/ strange concept I know.... :y
Actually, if the weather stays good maybe a barbie would be on the cards? :y
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Ok thanks Kev. :y
So that proves that, which is good. But it also proves plod spec is lower geared/higher rpm at 80.
Keeping things simple for a second :-[ an idicated 80 in an auto plod spec car gives 3500. An indicated 80 in mine gives lass than that. Needs another 250 rpm at 80. As I understand it.
Calibrated speedo may be the culprit
Yep, plod calibrated taken the error, or some of the error out. Lowering the indicated speed, appearing lower geared in comparison.
What's the error at 80? 4 mph...?
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Ok thanks Kev. :y
So that proves that, which is good. But it also proves plod spec is lower geared/higher rpm at 80.
Keeping things simple for a second :-[ an idicated 80 in an auto plod spec car gives 3500. An indicated 80 in mine gives lass than that. Needs another 250 rpm at 80. As I understand it.
Calibrated speedo may be the culprit
Yep, plod calibrated taken the error, or some of the error out. Lowering the indicated speed, appearing lower geared in comparison.
What's the error at 80? 4 mph...?
About that
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"CURRY" ....? ;D
Thought so. ::)
Or whatever.
You can experiment if you like. I'll stick to what I know, thanks. ;)
;D well apparently not "everyone" likes curry. :-/ strange concept I know.... :y
Actually, if the weather stays good maybe a barbie would be on the cards? :y
BBQ curry. Fantastic idea. :y
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About 3250 at about 80 on my 2.6 (getting near 85 on speedo)
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About 3250 at about 80 on my 2.6 (getting near 85 on speedo)
Same as Chris then. 4.22 diff. :y
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EPC does do Reg to Diff Ratio lookups if anyone needs any checking :y
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Might be worth a looksee JB :y OU54AEW.
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Might be worth a looksee JB :y OU54AEW.
3.70 LSD :y
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He just replied to my text. Speedo is calibrated with confirmation sticker on the dial.
Also the car is currently on auto trader. ;)
White 3.2 saloon. :-X
this was a 3.90 LSD
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and....
our mv6's
My 3.2 Auto Estate : 3.9
Her 3.0 Manual Estate : 3.7 non lsd :'(
my old 3.0 Auto Estate 3.9
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He just replied to my text. Speedo is calibrated with confirmation sticker on the dial.
Also the car is currently on auto trader. ;)
White 3.2 saloon. :-X
this was a 3.90 LSD
Yeah, well, just goes to show.... WTF do I know. ;D
Could have sworn it was lower geared. :-[
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taxi al wrote Yesterday at 21:50:
Might be worth a looksee JB OU54AEW.
3.70 LSD
Thanks for that JB :y
Nice to know its defo got an LSD 8-). Will reconfim rpm at 80 on way to work tomorrow :y
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FWIW:
3.2 manual, 3.70 diff, standard (original fit) wheels/tyres 225/55/16, close ratio 'box?
80mph = 3000rpm.
HTH,
Al. :y