Im looking at getting a 2001 or newer Subaru WRX.
First thing i plan to change will be the exhaust sytem.

As im new........try your hardest to understand where im coming from. This is all new to me.

I believe you can get aftermarket exhaust systems without the cat section. I have heard that it can be this that can cause detonation due to more free flowing gas down the exhaust and the turbo spins alot faster........or something like that.
Is this correct ?
Also what power gains do you get from fitting a de-cat system ?
Is it legal ?

If i was to fit an aftermarket exhaust sytem with the cat, could i still encounter detonation or not ?
Again, what power increase would i get from a system with cat ?

Any advise or info will be great.

Cheers
Marc.

 

Mines an STI MY03

You can experience DET with any de-cat mods to the exhaust

I just replaced the downpipe and kept the original centre section and this still created DET.. (it may have been there before.. I do not know).

The biggest benefit from de-catting is throttle response, overall power may increase as a result of the better flow, but it varies from car to car.

Yes it is illegal, and may result in MOT failure or spot fines if your police have cleaver roadside gadgets.

Milltek do a fast flow exhaust (they use it on the Type25) which would keep things legal and give you the de-cat feel you are serching for.

The prodrive system uses a fast flow downpipe cat, equally as good.

If you get a WRX the up-pipe can be replaced also... post 2003 STI's do not need this mod.

 

If you want to stay legal, keep the cat. But there are cats & there are cats... the standard ones aren't exactly good . Also, you have a cat in the up-pipe (before the turbo) as well as one in the downpipe (just after the turbo) & one in the centre. The one in the downpipe can be replaced with a high-flow one, and the up-pipe & centre section can go completely with the car staying totally legal, emissions-wise.
What frequently happens, though, and the 'det' problem, is that with the more freely flowing exhaust system, the ECU will allow the turbo to overboost (i.e. it spins up faster than the ECU is expecting). This can easily be countered by installing a Dawes Device to control this - either totally replacing the ECU's boost control, or plumbing it in in parallel with the ECU-controlled solenoid to simply work as a 'pressure relase valve' which will stop overboost from occurring, but allows the ECU to control boost most of the time; this will give better part-throttle response, but will not allow the boost to be raised any more as the ECU will simply flap open the wastegate... (a Dawes by itself obviously allows boost to raised to whatever you want).
For safety, replace system (up-pipe, dp, centre, backbox) with a single hi-flow cat in the DP, the rest free from bungs, and pop a Dawes in parallel with the solenoid, set up to stop overboost. That should give a significant improvement, and should still remain well within the safety limits of what the ECU is expecting. It may underfuel a little at bottom-end spool-up, but this shouldn't cause any mechanical problems at all (too low boost!).

 

does this apply for classics to? Does that mean there are 3 CATS in the system? im confused about the up pipe part...

 

No uppipe cat in a classic , just downpipe ( & center on UK cars )


Steve

 

cheers steve, beggining to think there were more cats on a scoob then in a vets