3 inch or 2.5 inch ?????

[KING PIN]

hey guys

I just wanted to know your opinion on exhausts ??? ... Presently I have a standard 2.5inch exhaust system on the car and I am thinking of putting in a 3inch exhaust system :-\ but am worried that it might be too big and will not have enough back pressure and it might not pull as hard in the bottom end ???

Thanks in advance for your opinion on this topic

[BC5RA]

This is going to be a can of worms..

[Guest the_return_of_the_jedi]

 BC5RA said:

This is going to be a can of worms..

true that..

sits back and watches with anticipation ;D

[Joker]

2.5 or waste more money on a 3

only dyno will tell ya any performance increase...

[Koom]

It all depends.

I also am finding it hard to keep my 3" system at a decent noise level. Having to now put on a proper muffler as a normal straight through one isn't enough and there's no straight bits left under the car for me to put in more silencers/resonators.

[WRXER]

As above, however I don't have a big bore so noise isn't much of an issue for me. On my previous 2.5" system I was getting exhaust fines as I had a Rage big bore with 4" tip.

3" if you are going to be doing lots more mods down the track, ie decent kw atw figures

[DRFVDR]

WRC spec cars run 2.5 "

nuff said

[BC5RA]

From what I've researched I say 3" from the Turbo to a necked down 2.5 inch large straight through muffler.

As exhaust gases get smaller when they cool, so needing the larger diameter at the down pipe and tapering it down to keep up velocity.

And to contradict this I run a full 3" system with one 14" resonator and an Jap style angle mounted cannon, mainly because I'm a totally irresponsible driver with no public regard. (and the car isn't a daily driver)

[Guest the_return_of_the_jedi]

 BC5RA said:

3" from the Turbo to a necked down 2.5 inch large straight through muffler.

+1 worked fine on my 89 gt.. had the group n downpipe and 2.5" straight through.

good stuff

[WRXER]

 DRFVDR said:

WRC spec cars run 2.5 "

nuff said

Lol not really, comparing a wrc car to a road car is far from applicable. Really depends on the setup he wants to do/direction of future mods.

[DPI]

 WRXER']

[quote name='DRFVDR said:

WRC spec cars run 2.5 "

nuff said

/quote]

Lol not really, comparing a wrc car to a road car is far from applicable. Really depends on the setup he wants to do/direction of future mods.

Unless you drive your car like a WRC car (3/4 to full noise everywhere, including round corners), this is a bad analogy.

[Koom]

 DRFVDR said:

WRC spec cars run 2.5 "

nuff said

They also run a restrictor on the compressor inlet which severely limits the horsepower limit. But if you freeboost through the midrange you can make a tonne of torque before the flow limit through the restrictor is reached.

[nzkaosnz]

find a copy of http://www.amazon.com/Maximum-Boost-Turbocharger-Engineering-Performance/dp/0837601606 and read it.

[Guest keltik]

3inch would be a waste of money in my opinion. Just make sure everythings heat wrapped and flows well

[DRFVDR]

OK OK

How about "most" Group N cars

and "Most" Pwrc cars

Run 2.5"

[Koom]

 DRFVDR said:

OK OK

How about "most" Group N cars

and "Most" Pwrc cars

Run 2.5"

32mm restrictor in intake.........

Same thing, they're never going to make more than 220kw atw. Even the ones that can afford to freeeboost past 30psi.

[Pappu1]

mate with a evo4 made 26kw with a 2.5 inch system...

now i know they not the same but the point is 2.5 inch will flow near 220kw easily for a street car..

end of the day depeneds what is ur planned outcome - if u want a 300kw drg wepon then u go for bigger of course but if u want a 220kw or so quick street car then 2.5 will be adequate + no loss of low rpm torque of the 3 that usually happens on small capacity cars like ours..

PS. i just had a 3 inch installed and immediatly gained a torque hole in the low rev area.. so im thinking maybe not really a good move since im only having a decent street car - as in drive to work in when i have to and not some track car where low end is not that much missed

my 2c

[WRXER]

Personally I didn't notice much difference with low down torque however that was with v1's and v2's where the td05's had a late kick anyways. This is always a constant debate this one, I regretted going with 2.5 on my previous wrx as I was planning my mods my 2.5" would be one of the bottle necks, however I ended up just getting this wrx which has a 3" and never looked back,

[Guest]

It would be interesting to see the comparisons on a dyno, same car, same dyno and just exchange in the 2.5'' with the 3.0''

[BC5RA]

It would be so negligible, its pointless.

It all comes down to overall setup.

[Koom]

 BC5RA said:

It would be so negligible, its pointless.

It all comes down to overall setup.

I concur.

[Pappu1]

for the same $$ i will go 3 inch ..but up to 220kw i wouldnt have any issues with 2.5 inch..

edit - the mate had 260kw not 26kw lol

[Guest DMSREX]

http://www.msengineering.com.au/exhaustsystems.html

Read this this he builts lots of road & track Subaru engines pretty good overview of what to look for in exhaust systems. Interestingly he recommends 2.5 system generally.