going to look at hopefull y my new g40 :-)

[Andy]

Your car really needs a proper setup Nick, though I must say I'm surprised that you're not getting any boost 'til 4.5k. What cam are you using?

[Robin]

Engine was built with high boosting in mind

cool at least you had a target, what parts have you used for the high boosting in mind?

[Nick_S]

252/276 schrick

To be fair its probably going into positive boost figures around 4 grand, but when its wet and dark at the time of having a test rag, you spend a lot more time looking where you are going.

[Robin]

good point...........................

aren't roads open during the dry and daytime in manchester?

[Nick_S]

When you have a car as loud as this is at the moment, best keeping to times when there are fewer people on the roads

[Robin]

surely its worse to drive a loud car at night as there is less traffic on the road to hide your loud exhaust!

[Phil]

Have to admit I've noticed the same thing, with the larger bore exhaust you dont get the same feel of low down torque than with a smaller bore system, remember a supercharged system works in the same way as an NA type lump.

I put a 2.5" exhaust on a near stock G40 a couple of years ago as thats all I had about at the time, and although it pulled harder at higher rpm, the low down grunt suffered.

And when I think back, my first was a 150bhp G40 on a 1.75" system, that felt very torquey, where as a car I've got now with the same mods and a 2.5" system and its as above picks up better at higher RPM but in exchange for a bit low down.

2.25" is good for 140-180bhp, and seems to be a good balance on midly tuned G40s I'd say.

Nick, get a 60.

[Yoof]

Not surprised you lost torque on a stock G40 with a 2.5" bore to be honest Phil...

All G40s running 170bhp+ generally have 63mm systems- with a smaller bore you may find bottom end torque to be better, but when flow is limited at higher RPM, power and torque suffer higher up the rev range.

Personally sacrificing a little low down torque for mid/top end power in a G40 is not bad thing, they wheelspin enough in 1st and second as it is. I'd like to measure the backpressure differance on a 1.75", 2", 2.25" and 2.5" system 

[benh999]

getting back on subject I may have just bagged myself a g40 :-)  All going well I pick her up on 4th Jan

[Yoof]

Good news Ben- bagged a good 'un.

To add on what I've already said, this backpressure argument with a larger bore system is b0llcks to be honest. The drop in torque Phil/Nick are experiencing is due to the A/F ratio changing due to a larger flow of air. If you consider 'boost' as back pressure instead of manifold pressure- you've both fitted a larger bore exhaust system- Nick has mentioned a drop in boost pressure- ergo an increase in flow through the engine.

Unfortunately the poor old Digifant ECU can only work with what the MAP sensor tells it, so even though you're flowing more air, have a lower manifold pressure reading, you actually need more fuel. Torque curves can be massively affected by A/F ratio- my Clio for example 'comes on cam' at 5,000rpm.... does it bollocks! It's a marketing thing which Renault did to give you a kick in the back once they actually add some fuel in above 5k.

To conclude, you won't loose any torque by fitting a 63mm system or a decent 4 branch, providing your car is mapped properly afterwards. I know neither of the above cases have been, so a comparison between the two is unfair.

Nick- I'd check your cam timing too, you should see positive boost pressure well before 4500rpm.