what exhaust bore should i get?

[swiftg40]

Evening all,
im having a full system from manifold back with de-cat made next monday but was wondering what bore to get?
engine has standard exhaust manifold, chip, 65mm pulley, front intercooler, r1 charger.
The guy making it recons a 2 1/4 inch will be fine.
Anyone got any advise, is this size ok?
i'm not goin to be doin many more mods possibly a gt inlet
cheers

[Yoof]

Ours are 2 1/2", if you want to get above 160/170bhp then I'd go for 2 1/2". Obviously be good to get a manifold at some point too.

If you're sticking with your current spec then 2 1/4" should be ample, the stock G40 manifolds are good for 165-170bhp.

[Dirty Slag]

How many silencers are you using?
You need some back presure else you can do more harm to your performance than good!
Even though its a boosted engine you dont get the same results as a turbo car from using a larger diameter exhaust!
2 1/4 with a single free flowing silencer will be more thann enough as its only a small cc engine your just not shifting enough gas to warrant bigger pipe work!

[swiftg40]

i'm having a center and rear silencer just to keep noise down a bit. As for power i dont think i'm going to go mad with mods (sticking to under 160-170bhp), next on the list is a diff to get the power i have to the road as it just spins everywhere which is good fun but doesnt get you nowhere fast especially when its wet lol.
Think i'll go for the 2 1/4 inch then.
Cheers for the help

[dub-disaster]

whats the rules of bore size on turbo engines then ?? ive currently got 2 1/4 inch bore with two silencers i am putting a ko3 on is it worth going to 2.5 inches twin silenced or shall i just stick with what ive got ??

[Yoof]

If you're going for big numbers switch to 2 1/2" 

[dub-disaster]

will do i would definanlty like the big numbers

[Dirty Slag]

But what do you call big numbers?
I built a turbo crx last year these are 1.6ltr and it made 353bhp using 2 1.4 inch single silencer system!

[Andy]

On a K03 turbo'd G40 a 2.5" system works well, dyno proven.

My own car's got a 2.25" system on, and spools 100-200rpm later than Robin's car which is an identical spec apart from the ECU (I'm on Emerald vs Robin on Digifant - though I mapped both cars) and exhaust. They both make similar power, though Robin's comes in earlier thanks to earlier spool-up.

Clearly no-ones suggesting sticking a 3" or bigger system on a 1300cc lump, but the only differences people will notice between 2.25" and 2.5" on a 150bhp G40 are in terms of noise.

[Jake]

I'm running a 2" on mine, as thats what was advised by longlife. Had the car rolling roaded at 150bhp at powerstation. Is the 2" likely to be restricting it at all? And I may be looking into bigger power after christmas by fitting my lysholm kit...

[Andy]

If you're going to run the Lysholm at high boost and plan further mods, I'd go for 2.5" and twin silencers. If you're only aiming for 170bhp, I'd still consider moving up to 2.25".