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[ngrainqey]

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

[markey mark]

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 !  

[ngrainqey]

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 !  

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!

[Albatross]

"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.


 

[Albatross]

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 !  

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.

[ngrainqey]

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 ?

[Albatross]

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 ?

Monaro VXR

That's definitely on my list. I just need to check my bonus this year.

[ngrainqey]

lol ordinary monaro is fast enough!

[feeutfo]

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!

[ngrainqey]

id rather have a commodore (the 98 vt version though)

[ngrainqey]

...or maybe the vx/hsv version

[Kevin Wood]

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

[feeutfo]

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...

[Kevin Wood]

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

[omegadan67]

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.