stonejedi

iTrader: (51)

its all in the title please help

Varboy

After about 350bhp, an exhaust diameter of less than 3" will become a restriction. Of course you can achieve more than 350bhp if it's less than 3 but being 3" would be beneficial.

S500BE

was interested in the same thing i have a full magnex system think they are 2.5" and would be a shame to change it....

andy97

iTrader: (1)

Andy Forrest has more than 450bhp from his 2.5" exhaust spec C car

renno rannes

Ill also say try the 2.5" up to 400 or more even. Dont see it as a major restriction if its a full decat.

Renno

catons scooby

ive had over 400bhp with a 2.5" on a my99

stonejedi

iTrader: (51)

this is all a bit interesting as when i spoke to a tuner he said to me around 350 bhp 2.5 inch is fine but if i am looking more power than that <which i am> he said i would need a 3 inch. i have all ready got a afterburner back box a decatted middle box and resnator and prodrives performance cat on the down pipe which was already on my car as part of the ppp conversion.i dont really want to change my exhaust if i dont have to as i like the sound and polished tail and back box of the afterburner

cookstar

iTrader: (6)

Interesting thread, would be nice if the tuners gave an opinion as I really dont want to change mine.

stonejedi

iTrader: (51)

thanks for your replys just wondering if i do keep my exhaust would it be worth changing my manifold to say one of those tubular ones and if i did how much power should i be looking from that with my exhaust?

bighead

iTrader: (1)

20-25 bhp

silent running

Well having junked my lovely sounding full-length 2.5" system (on another car) for a 3" straight-through side-exit system, I know the pain of whacking on a massive zorst in an effort to maximise engine tune, only to find the difference it makes is not worth the headaches on the motorway or the soundcheck problems at tracks.

If you like the sound of your system at the moment, keep it on, get the engine how you want it and see if it performs well as it is. Later on if you're desperate for more, changing the exhaust is easy enough. Putting on a brand new exhaust then finding out it's far too rowdy for your liking is gutting.

stonejedi

iTrader: (51)

thanks for the advice i am going to keep my set up but will still look into changing my headers on my car and see if that will componsate for the .5 lack in diameter size.

Turbotits

iTrader: (2)

i also have a 2.5. 370's not a problem. Exhaust not holdong it back at all

silent running

Well mine's a kind of mix and match system on my MY98 WRX. Harvey's ported and wrapped headers and up-pipe, TD05-16G turbo, GGR sports cat downpipe, H&S straight through centre section and up until recently a standard STi backbox. All was fine and dandy although it was a little laggier than it should have been. A simple change to a Prodrive 'WR Sport' backbox off a newage made a hell of a lot of difference to spool up - previously I was seeing 1 bar at around 3200 rpm then full boost (1.45 bar) by around 3600. The freer flowing backbox has brought the 1 bar point right down to around 2900 which is very noticeable, as well as the full boost coming down the range by 200-300 rpm. So my conclusion is that the STi backbox was strangling things. It also has virtually eliminated the compressor surge problem I have been struggling with as well - it just couldn't be mapped out, but the backbox swap did it. That WR Sport box was the best £40 ebay bargain I ever had!