Exhaust Piping diameter Question.

I am looking at a cat back system and just curious what the differences in 2.5in pipes vs 3in pipes would be? Is that .5 of an inch that much of a deal?

Also the downpipes come in both 2.5 and 3in also, so the turbo back could be 3in pipes.

thanks

 

performance wise, i believe it will make more of a difference at high modification levels

 

I was kind of thinking that. Couldnt see spending the extra money on a .5 inch of a difference. Now I just need to talk to the wifey, so I can buy my catback... hnoes:

 

From what I read, the 2.5 diameter pipe is capable of supporting up to I think 350 or it might be 450 WHP, I honestly don't remember. After that you will lose performance due to to much backpressure.

 

I've read that a 3" pipe if improperly designed can cause too little restriction at the low end, reducing some torque at low rpms. This doesn't seem to be the case with WRX exhausts though. a 3" pipe will also be louder.

 

Don't think you'll have any problem with either of the two. I think that if you ever plan on doing a bigger turbo, you'd be better off with a 3" piping, but like Jason said, the 2.5" piping supports well into the upper 300 whp range. I think Cobb's site has something about it, let me look around and I'll see if I can post a link for you.

Here's the link:
http://www.cobbtuning.com/tech/exhaustdesign/index.html

 

i guess at this stage, u might wanna consider how loud u want ur car to be cuz the performance difference will be small

 

That holds true for naturally aspirated cars, but turbo cars don't require backpressure from the exhaust.

 

if you want loud buy my axle back

 

i dont think it would make a large difference if you went 2.5 instead of 3, i know i plan on having a do-it-yourself full catless 2.5 and i think that should be fine for my eventual goal of 300-350whp.



Alex/WRX-WRC

 

As previously stated above, 3" is loud!! Dont go 3" if you go on road trips every week!

 

2.5 is also loud. i have a homemade catback connected to the stock dp and its pretty loud. im almost scared to get the dp cause i dont want the car that much louder than it already is. but i got a dual baffle silencer for mine that cuts all the noise away on road trips.

 

if you spend the money and get a nice catback most of them come with a silencer..thats what i use on long trips and it makes a big difference

 

i am getting a 3" myself this weekend turbo back and i am pretty sure its gonna be LOUD. If you dont hav ea huge mod list planned im sure the 2.5 would serve you just fine. Like everyone said its all about noise you want.