I've noticed that alot of companies are producing exhaust systems for the WRX with 3" piping. www.spdusa.com and scoobysport both recommend 2.5" piping because it supposedly allows the turbo to build boost quicker than the 3" and the 3" doesn't provide any advantage at higher rpms either (assuming you're using the stock turbo, which I will be doing). The exhaust shootout results in Turbo magazine didn't seem to agree with this opinion as some of the 3" designs outperformed the sole 2.5" at lower rpms. Does anyone have any experience with this? Should I stick with 2.5" or go with a 3" design?

 

me general rule is "go with the largest you can stand to hear"

 

I installed a 3" catback on my friends car last week and it feels like it gained power. It sounds really nice. It came with a silencer too just in case you get tired of the rumble.

 

2.5 is good for what you really need. 3 inch is nice but unless you have 300+ hp then it is not necessary.

 

when we had a dyno day at pruven performance arranged by "AllfriedEggs"
approx 30 scoobies the dyno results showed that the
2.5 exhausts retained more torque but lesser hp and the 3" exhausts lost torque but got more hp ...

Andy...

 

I was lucky enough to run this turbo back system on my car last year it was great...low end top end really made a differnce the butt dyno liked

areg

 

torque is what you need

 

http://www.turbomagazine.com/tech/0212tur_exhaust/
Here ya go. Look at the specs of the Blitz exhause and compare them to the rest and see which on maks more torque.

 

I thought that the bigger the better for turbo's? Anyway, isn't maintaining a good, steady flow of exhaust gases at a constant velocity supposed to be the key to good power? Just wondering.

 

at the dyno day we were all looking and comparing the dyno results etc with our mods and noticed this

if i knew the exact reasoning behind this i would let you know !!

but i don't i'm just going back what we saw etc

my dyno sheet is posted in this link
https://www.i-club.com/forums/showth...0&pagenumber=2

maybe its cause we had modded wrx's with similar mods like vf23's hks boost controller set the same but just some of us had 2.5" exhaust and some had 3" systems...

Andy

 

IMO- You'd want to run the largest exhaust piping within reason. for example 3" tubing is popular. What you DONT want to do is run with no type of downpiping as this could lead to turbine over run and be potentionally fatal for the turbo. Turbos love a none restrictive exhaust system but an exhaust system nothelest. Smaller exhaust piping will lead to back pressure and that could lead to the dreaded boost lag.

What is tend to see here on the forums is that a lot of people here think of upgrading the turbo right away for a larger unit when I feel one should be thinking about freeing up all restriction in the exhaust system from the exhaust ports to the muffler tip. What about an length header? I know it's expensive but it shouldn't be over looked. Imagine what your car would run like with absolutely no restrictions on your car exhaust and intake, the engine would be zinging to the redline. Gadzooks!

My 2-scu

 

Okay, it looks like 2.5" is the winner for my setup. I'd rather have torque at the low end than hp at the top. Thanks.

That's what I would think too. But, www.spdusa.com claims that a certain amount of backpressure is required for the turbo to spool quickly and 3" does not produce the "ideal" backpressure.