peter zippy reid

iTrader: (25)

Hi im running over 400 bhp on my 03sti jdm should i change to 3"system when i go fmic

yabbadoo4

iTrader: (8)

im pretty sure its advised to go 3" at the 400bhp mark to see some benefit.

The Pink Ninja

iTrader: (23)

mainly depends on the brand and how restrictive the backbox is really

peter zippy reid

iTrader: (25)

System just now is full decat with group n back box
Md321h twinscroll
650 injectors
Rcm big trumpet

scotty boy 80

iTrader: (5)

If your going for it Peter I'd probably take the back box if you choose to sell it mate

TonyBurns

iTrader: (3)

At that power level a 3 inch is recommended, I have a brand new 3 inch H&S with sports cat gathering dust at home if you are interested?

IainMilford

iTrader: (15)

A friend got a 20bhp increase when he went from a 2.5 to 3" exhaust at over 400bhp

TypeR99

iTrader: (2)

I had a 3" to 2.5 decat and 2.5 to 3" system on mine and was advised to look for a 3" system @ 400+

Still cant understand why the system has a step down to 2.5 where the cat pipe meets the centre, about 4" long then straight back up to 3" again, unless its designed to mate to a stock system.

I know how restrictive an exhaust can be, my last type r had a nurspec and during mapping we tried it with the bung in/out of the backbox and it made 20bhp difference due to the restriction

peter zippy reid

iTrader: (25)

Thanks tony but it will be full decat if i do it

Dave Y

iTrader: (52)

So what 3" exhaust system gives the best results?
Is full decat the way to go?

scoobygaz1

iTrader: (3)

I'm a full 3" with decat running 507bhp with cobra back box! 400+ you'll see a Diffrance with a full 3" system

peter zippy reid

iTrader: (25)

Does going from 2.5" to 3" affect torque

Paben

iTrader: (5)

It did with mine, not really for the better. I was running a full decat 2.5" H & S with a Harvey up pipe and manifold at 414ft lbs. When the manifold cracked I changed it for an RCM GT Spec Gen 2 and up pipe and 3" H & S system. The torque increased just 11ft lbs but moved the spool point up 500 revs. Not the difference I was expecting or wanted. Those in the know reckon a Harvey up pipe would improve things considerably. Since Simon Roe sadly passed away I have not been inclined to try this option as it would require a map adjustment, so it remains unproved.