so i'll be buying a 2.5" CBE to replace my 3" CBE that i have now as i'm not looking to run more than around 300 hp and feel the 3" reduces drivability and the power curve throughout the power band except at close to redline. Would you think i should get a 2.5" downpipe preferably shorty non-plate design (bosal i think makes one) and be leaving the 3rd cat in the midpipe as from what i've read, it doesn't add anything to the power and is not a restriction. Or should i just wait on the DP and go for possibly a openecu style homebrew tuning and reflash it myself using maps downloaded on openecu or the other possibly solutions or a used cobb AP.

 

so i take it everyone thinks 3" exhaust is the best even though most won't need the diameter, and be catless completely. Hmm anyone know anything about pro's and con's of running this setup vs. the typical 3" tbe, and cobb ap (stage 2 whoa!~)?

 

I'm curious to this as well. I'm planning to get a 2.5" downpipe and leave the 3rd cat in with a cobb AP later down the line. Is this worth it? because I'd like to keep it stealthy with all the nosey California cops around.

 

Bosal Up Pipe (looks like the STI stocker)
Gutted STi Down Pipe
Borla Hush catback 3"
Samco i/c hoses
Cobb AP Stage II (cali 91oct map)
<<<<<<

It's still worlds better than the stock set up. My turbo is at full boost between 2,800-3,000RPMs and pulls all the way to 6,000RPM. It's pretty quiet and isn't even that loud at full throttle. I've been running this set up since June and I couldn't be happier with it. Everything cost me something like $1600 and I don't plan on adding any other mods.

Hope that helps.

 

Bump for additional question. Does anyone know how that 2.5 inch exhaust will mate to the stock third cat? Is there any fitment issue or is just a quick swap? I have the Bosal Shorty DP, third cat and soon 2.5 inch catback. TIA.

 

A 2.5" exhaust flows more than enough.
I would go with the Cobb downpipe.
Anything bigger than 2.5" and your lowend torque will
suffer and your drivability will go down the tubes.

 

That is a myth. For turbocharged cars, you want as little backpressure as is practical to minimize turbo spooling and response. 2.5" is okay but I recommend a 3" turboback system for maximum power and drivability with either the 2.0 liter or 2.5 liter turbo engine. Properly tuned, the 3" system works well with either stock or upgraded turbos.

The only drawback to 3" turboback systems are possibly higher cost over 2.5" and rubbing issues (chassis) on some less well-designed systems.

--
0==WW==0
"…axles of evil…" - george w. bush

 

It's far from a myth.
If you have a EJ20 and the stock Mitsubishi TD04H turbo than a
2.5" exhaust flows more than enough.If you are upgrade turbo's
than you should go with a 3" exhaust.

 

just curious, but do you have any sources to where you found that info?

 

^^^
This is not true. Turbocharged vehicles do not lose power with tubing larger than 2.5" unless something is drastically wrong with the tuning. Backpressure after the turbo is always undesirable, although it can never be reduced to zero in a car with a full-length exhaust system.

--
0==WW==0
"…axles of evil…" - george w. bush

 

or catalytic converters...

 

I don't know how much of a difference it is with a 2.5 and 3 inch. But what I did was get an up-pipe/downpipe and leave the catback stock (I didn't want the loudness). And the car seems to pull just as hard as another with the same mods and 3inch catback.