Omega Owners Forum
Chat Area => General Car Chat => Topic started by: Diamond Black Geezer on 26 September 2016, 16:44:18
-
Get a cuppa, and take a seat... ;)
Much has been said on boring/honing your throttle body to increase the magic power... Its something which most claim will realistically only release 1 or 2 bhp from your engihe, about the same as a polish, or a new set of tyre valve covers. But anyway, that's all 'opinion' so with limited knowledge I thought I'd see what I could theorise.
The C and X 25XE was used in fwd applications, in Cavs, Calibras and Vectras as well as rwd. On paper, in the brochures these produce the same power, though there is debate that the rwd engines always made a little more power, due to their superior intake system. However, for the purpose fo this exercise, these engines are 'the same' power outputs that's what Vauxhall claim.
The fwd engines use a single butterfly valve, whereas Omegas use a twin affair, of course. On top of that, the multiram intake should smooth out the torque curve, while not actually adding power, makes for a more driveable engine. Doing the basic maths the fwd engines have, when enlarged, a bore of
TB bore fwd V6 68mm
sq. area 3631.68 mm2
TB bore rwd V6 56.5mm
sq. area 2507.19 mm2 (but there's two of them, so...) 5014.38 mm2
or, rwd engines have what seems a massive 38% larger air intake surface area. That means nearly two-fifths more air can be sucked in (well... I say no, because the engine will only ingest 6 combustion chamber'sworth of air at any one time, but it is breathing 'easier' by 38%, shall we say?)
The fact that there's a barely perceptible difference between the engine outputs of the fwd and rwd 2.5 engines means, surely, this throttle body enlarging must account for....well, nothing?
Ok, let's make a theoretical assumption - the rwd V6 throttle body gives a whole 10 bhp extra over its fwd brother. That would equate to...
Enlarged TB Diameters...
68mm - 56.5mm = 11.5mm difference
11.5mm / 10bhp = 1.15bhp per mm of throttle body diameter increase.
So the rwd standard 54mm throttle body which can be enlarged to the above mentioned 56.5mm means
2.5mm difference diameter, or 2.5 x 1.15 = 2.9bhp difference.
That 2.8bhp extra based of, remember, if the fwd and rwd engines differ by 10 bhp. If that is only 5bhp, that's 1.44 bhp, if it's only a couple of bhp we're down to half a bhp!!
I'd welcome any input on this, with regard to anyone with a better grasp of GCSE Maths than I (which I suspect is most people :D) to pick up on any errors, or even if you think there's flaws in my theory. Rather than doing it for real, thereby allowing placebo effect to take over I thought I'd play around with a notepad and biro.
You can go to the toilet now!
-
The thing is, if the throttle body isn't the weakest link in terms of gas flow, (which I suspect is the case. It's normally the valves / ports / cam characteristics) then it'll make the square root of bu66er all difference anyway.
When looking at the larger area of the RWD V6 throttles, bear in mind that you have 3 cylinders pulling through each throttle rather than 6 cylinders through the comb9ination of both. This does make a difference.
I suspect there is nothing to be gained by modifying the throttles and plenty to lose, in that, if they don't close perfectly, you have a massive air leak and drivability problems and if the two sides aren't perfectly matched it'll run like a jelly on a plate.
-
Get a cuppa, and take a seat... ;)
Much has been said on boring/honing your throttle body to increase the magic power... Its something which most claim will realistically only release 1 or 2 bhp from your engihe, about the same as a polish, or a new set of tyre valve covers. But anyway, that's all 'opinion' so with limited knowledge I thought I'd see what I could theorise.
The C and X 25XE was used in fwd applications, in Cavs, Calibras and Vectras as well as rwd. On paper, in the brochures these produce the same power, though there is debate that the rwd engines always made a little more power, due to their superior intake system. However, for the purpose fo this exercise, these engines are 'the same' power outputs that's what Vauxhall claim.
The fwd engines use a single butterfly valve, whereas Omegas use a twin affair, of course. On top of that, the multiram intake should smooth out the torque curve, while not actually adding power, makes for a more driveable engine. Doing the basic maths the fwd engines have, when enlarged, a bore of
TB bore fwd V6 68mm
sq. area 3631.68 mm2
TB bore rwd V6 56.5mm
sq. area 2507.19 mm2 (but there's two of them, so...) 5014.38 mm2
or, rwd engines have what seems a massive 38% larger air intake surface area. That means nearly two-fifths more air can be sucked in (well... I say no, because the engine will only ingest 6 combustion chamber'sworth of air at any one time, but it is breathing 'easier' by 38%, shall we say?)
The fact that there's a barely perceptible difference between the engine outputs of the fwd and rwd 2.5 engines means, surely, this throttle body enlarging must account for....well, nothing?
Ok, let's make a theoretical assumption - the rwd V6 throttle body gives a whole 10 bhp extra over its fwd brother. That would equate to...
Enlarged TB Diameters...
68mm - 56.5mm = 11.5mm difference
11.5mm / 10bhp = 1.15bhp per mm of throttle body diameter increase.
So the rwd standard 54mm throttle body which can be enlarged to the above mentioned 56.5mm means
2.5mm difference diameter, or 2.5 x 1.15 = 2.9bhp difference.
That 2.8bhp extra based of, remember, if the fwd and rwd engines differ by 10 bhp. If that is only 5bhp, that's 1.44 bhp, if it's only a couple of bhp we're down to half a bhp!!
I'd welcome any input on this, with regard to anyone with a better grasp of GCSE Maths than I (which I suspect is most people :D) to pick up on any errors, or even if you think there's flaws in my theory. Rather than doing it for real, thereby allowing placebo effect to take over I thought I'd play around with a notepad and biro.
You can go to the toilet now!
You cant calculate it that way, your assuming any increase and decrease per mm is linear, its not, its relative to what size area volume your starting or finishing with, remember π r 2 (Pi R Squared), As where talking about TB's we are talking about an outside increase in the outer volume area, ie an increase of 1mm added to the Radius of 49mm (now 50) gives an increase of xyz% another 1 mm (now 51) will give a higher than another xyz% increase, and so on.
The Enlarged Twin TB's I recently sold on here, gave a good 15% extra Air Volume despite only a few mm increased diameter.
-
AFAIK it`s the exhaust manifold that is the restriction on these engines so no matter how much magic you work on the inlets it won`t really do any good.
Even if you could get another 20bhp it won`t feel that much different, enjoy it for what it is, a comfy, capable 2 ton saloon :y
The best mod you can do is a ex plod LSD, these engines like to rev and the shorter diff will feel like a far bigger improvement than anything you can do with the inlets ;)
-
My eyes started to glaze over, but luckily I'd finished my cup of tea before I got to the bottom of the page :)
Theories are all good and well..... how's this for one? My SRI Vectra (FWD) has the same engine and goes faster than my Omega (RWD), and this I put down to the size of the bodywork. So, to make your Omega faster and more powerful, you could just remove all the seats, interior trim and other fittings, and save the batteries in your calculator.
I'm ready for another cup of tea now, so looking forward to more theories :y
-
As above. The easiest way to go faster, and cheapest, without trying to change aero-packages, and consulting mathmatical theory.
Is make it lighter.
-
Ok going from a standing start the vectra is faster, what about a rolling start?
Are the engine maps the same?
-
Fabulous inputs, chaps. all gratefully received. I'm also none have died of old age reading this (well, not that we know of :D)
I'm aware my maths is/will be flawed, as you say zirk, the pi needs to be taken into account/used better, and that's something my rusty maths just wasn't able to comprehend.
The 'add lightness' argument is, more than valid, as is the diff, which I've often debated sourcing, but knowing I'm sending engine revs up at motorway cruising does niggle me. I think someone posted a graph some time ago about this.
But bringing it back to specifically the throttle body enlargement argument, can anyone offer a better figure than I have of how much larger the rwd intakes are, versus the fwd? Aware than this is not directly proportional to engine output, of course, but my figure of 38% is out, I am to understand. (However, "square root of bu66er all difference" as Mr Wood suggests sounds like very close to the in practice difference ;))
Thanks for your patience, and for entering into this little scientific debate. :y
-
Well Ive fitted Enlarged TB's, more than once, twice on a 3.0 and one on a 3.2 Manual.
Modded TB's, Ported and polished Inlets, K&N, Re Chip on there own make the 3.0 a better experience, idealy add a slightly tuned cat back system and it starts to come into play nicely, with the added benifit of improved mpg.
Remap a 3.2 with the above, and you really can notice and feel the difference.
As for the Vectra, got one of them, 3.2 Manual Vectra C Elite, in standard form, and I can honestly say my 3.2 ExPlod Manual Omega (With the correct 3.7 LSD Ratio) with the said mods will eat the Vectra for breakfast. ;)
-
work out the valve curtain area based on the optimum 10.2mm lift......(this is where curtain approx. area equals port size).....then make a decision
-
:y Very interesting. When you say 'optimum lift' - does that refer to the lift of the exhaust cam with 'G cams' fitted, also? (I suppose this would also alter things, versus A or J cams?) according to Mr Google a 10.2mm lift and the valves are 29mm diameter, at C = 2 pi r (yes, I had to look that up! :D) the circumference is 91.11mm, so the Valve Curtain Area is 10.2 x 91.11 = 939.32 mm2 I think? :-\
And to add another dimension - are 3.2 throttle bodies the same diameter as 2.5/3.0? knowing how they tried to 'free up' some horses on the later engines, just wondered if they altered these when they went over to DBW throttles?
-
Jesus H Christ ::)
Looking at this thread and the one about fuel trims and super unleaded, it sounds like young DBG isn't getting enough nooky at home too me :P ;) :D :D :D
-
You guessed! :D
-
Jesus H Christ ::)
Looking at this thread and the one about fuel trims and super unleaded, it sounds like young DBG isn't getting enough nooky at home too me :P ;) :D :D :D
Or he's become Webby...
Talking of whom :-\
-
Oh, Webby is my Obi-Wan/Yoda :y
As you say, not seen him on here in a good while, yes.
-
Jesus H Christ ::)
Looking at this thread and the one about fuel trims and super unleaded, it sounds like young DBG isn't getting enough nooky at home too me :P ;) :D :D :D
He was probably too busy following the instructions to realise she had fallen asleep ;)