I no longer use my 2002 wrx for a daily driver. So I am building it for rally. I currently have 3.2 inch downpipe and 3 inch exhaust. I've been told by a couple rally drivers to switch to a 2.5 inch exhaust for more torque. So anyone have any suggestions or opinions on which 2.5 inch exhaust systems they like best?

Also, I was curious, is it required to have a muffler or cats on a rally car? I understand that they must be street legal since they are on public roads while in transit. But rally cars are so loud which leads me to believe that they don't have mufflers.

Thanks for your help!

- Jeromey

In general, on a WRX in PGT you'll run some downpipe, a race cat (required by the rules), and just straightpipe other than that. The best bet would be to get a downpipe of some sort, and have the rest of the exhaust made for you from 2.5" stock at an exhaust shop. Very few rally cars have mufflers, mine has the cat where the muffler would normally be, but no muffler.

Jay

Thanks! That's very helpful!

On the rally car you want to stay away from "an exaust shop", or most aftermarket systems look cool but..., you need to find someone with rally experiance, or learn exactly what to do and find a good race prep shop to do it to your spec.


2.5'' is best, will flow for 600hp no prob, and the diameter is nicer than 3" because you can tuck it up into the chassis much easier.

Get a CAT like this one.

http://www.davesport.com/cgi-bin/davesport/DCAT325.html

At the very least, it should be all metal, this is the cheapest one I've found. Mount it all the way at the back, no muffler needed.

I make them(exhaust systems) in two peices, a short 12" long down pipe with a slip joint and OMP spring clips to hold tight connecting to the rest of the system, the back half should be double skinned on it's lower half.

I make the hangers from stright tube stock(no retaining bulge and lighter) and use those HD hairpin style clips to secure on rubber hanger.

That way when you have to do repair, it's two spring clips at the DP, and a few clips from the hangers and your off in 10 seconds. The short 12" DP is nice as it can stay on for trans swap.


pete

A couple pgt cars put the Cat at the end of the exhaust system.

Most PGT/Group N cars run a 3inch downpipe, 3inch intermediate pipe, into a 2.5inch axleback. They do so you have some backpressure left. :devil:


-Mark
MAPmotors.com

A couple pgt cars put the Cat at the end of the exhaust system.

I'm told this is the way to do it.

A couple of the cars on the SCCA circuit sound like they have the 2.5 ScoobySport system.

Aww man not this again!

"They do so you have some backpressure left"

NO. 2.5" exausts are used due to size. There is no reason to wnat backpressure in a turbocharged gasoline application. PERIOD! There is no use of the pressure waves to increase scavenging at a particular RPM. Its just not effective.

SEE:
http://www.eng-tips.com/viewthread.cfm?qid=86504&page=1

enjoy!

first of all.
read the rules before you build anything.

PGT = you have to use the stock up pipe
downpipe back is free
32mm restrictor on turbo inlet

Open class = free exhaust, turbo, etc
34mm restrictor on turbo inlet
I run in PGT
have a 4" bellmouth downpipe into 3" high flow cat and 2.5" out the back

my exhaust is a rally application, not typically sold for street models.
got mine at: www.ionperformance.com


Many put the cat at the back of the exhaust setup just in case it takes a hit an is punctured/crumbles - it wont be able to "clog" up the rest of the exhaust system.

I use 2.5" out the back as there is literally no room for 3"

cheers
jamie - #215
www.subiegal.com
2003, 2004 NorPac PGT Champion
2004 Western States PGT Champion