Exhaust 2.5" 0r 3"

[Crawford_S2]

Bit confused, loads on here have had exhausts fitted from longlife and most went for 3" as far as i can see. I emailed the web site for a quote and got a reply from the london area branches saying that they would do me a 2.5 cat back no bother but would not recommend a 3" system as it would effect performance

I have an ABY with a homefry and k&n so should be about 280ish but they said 350 on for a 3" and under that it would lose performance. Thing is i am on here a bit so chances are i will be modding again soon and another 100bhp will be likely so am loath to fork out for the smaller system if it won't give me any scope for upgrades.

What are the boys on here with 3" systems running power wise and do you all think this is toss or quite right? Personally thought it might be something to do with the difficulty the 3" system presents fitting but like to think the advice would be purely on whats best for the individual.

Any input much appreciated, just not sure what to go for now

[Jas11n]

The way I've always understood it is:
Chavs with NA saxo's and the like, big HUGE exhaust = silly, can reduce power.
Us guys with turbo'ed cars = bigger the better, turbo needs to be able to breath.

At least that's what I've read on here from the "tuning" gurus.

[Crawford_S2]

The way I've always understood it is:
Chavs with NA saxo's and the like, big HUGE exhaust = silly, can reduce power.
Us guys with turbo'ed cars = bigger the better, turbo needs to be able to breath.

At least that's what I've read on here from the "tuning" gurus.

Thats always what i thought but I can't argue with the dude who does it for a living before I get more feedback really, they know its got a turbo i assume as i told them its an S2 and they have done a few on here by the look

[caterpillar]

for the 1,8 and NA 2,0 liter 2,5" tubin,and for all over 2,0 liter ONLY 3" exhaust:mischeif: ....and for extrem turbo use(500+) i will rekomend 3,5"(89mm)
for NA engines use headers made of diesent tubin and 2 big mufflers.... for turbo use only 1 muffler....
i use 3" on my 2,2liter with 1 muffler( a reallly big muffler), and the sound are 100db....but i may have 9000rpm.....hehehe.

[phil2.016v]

Hi Crawf,

I've got a turbo back 3" Longlife system on the Avant, feels much better than it did before even with the de-cats. Still got good low end and it revs better with more of a kick when it comes on boost. Seems ok to me. Just need to send the ECU off to Paul and I'll dyno it and let you know. :mischeif:

Cheers
Phil

[1975DCS]

According to people (tuners and motorsport competitors) I spoke in the past they say that a too big exhaust will lose your off-boost performance while not gaining much on-boost, because if it is big enough, it is big enough...

Most recommend (a true) 2,5 inch up to 350 bhp and 3 inch upwards. Most also recommend to use a very good downpipe. Or to go big near the turbo and reduce diameter to the back. With my previous Opel most took 2,75 downpipes followed by 2,5 inch exhausts.

If you are planning 400 bhp I would go for 2,75 or 3 inch.

Funny: ever seen a WRC or Rallycross car? So small that exhaust! And still 700Nm+ and 300-550 bhp (on their 34 and 45mm restrictors)!

[Billman]

Can i ask a small question here. On th eRS2 what Twin-Tail pipe diameter are you using?

[Jon441cc]

Hi Crawf,

I've got a turbo back 3" Longlife system on the Avant, feels much better than it did before even with the de-cats. Still got good low end and it revs better with more of a kick when it comes on boost. Seems ok to me. Just need to send the ECU off to Paul and I'll dyno it and let you know. :mischeif:

Cheers
Phil

Glad you like it Phil have you fitted the tailgate yet?

[phil2.016v]

Glad you like it Phil have you fitted the tailgate yet?

Yeah great tool Jon, cheers for that!! I haven't fitted the Tailgate yet mate, just waiting to get it sprayed.

[Crawford_S2]

Anyone else got any input? Must be loads of longlifers on here.

[blown_vr6]

The first few inches after the turbine housing are the most important - you could go 3" downpipe and 2.5 or 2.75 all the way back.
Personally i think that its a load of old ball cocks about turbo's needing backpressure in the exhaust - the bleeding turbine housing will provide all the back pressure you need.
I changed my exhaust on my homebrew 900 turbo to a 3" JT and there was no loss of low down torque.
Spool up was increased and it was alot more free flowing up top too.

Pete.

[Crawford_S2]

Hmmm so still no idea what to go for but still edging toward 3" cos the width is all important as my nan used to say

[blown_vr6]

3" all day long mate...

[sorens2]

3" all the way or 3.5"

Søren S2

[phil2.016v]

Go on, you know you wanna 3"