Quiet 3" backbox for classic Impreza, Revolution?

Andy916 · Post by **Andy916** » Fri Feb 27, 2009 9:15 am

Hi Francis,
I have a bung in there at the moment, which takes the 5" down to about 2.5", and doesn't seem to harm the low/midrange at least. Not sure how much this is going to affect the mapping though - I presume it'll need a map tweak ideally to optimise for one or t'other.
Andy

Fast Eddy · Post by **Fast Eddy** » Fri Feb 27, 2009 11:28 am

Andy,
Try a 3" bung just to cut the resonance down in the existing tailpipe or change the tailpipe for a twin wall version to do the same job.
Eddy

ScoobieWRX · Post by **ScoobieWRX** » Fri Feb 27, 2009 2:50 pm

I would have said that if you have with a 3" exhaust system so long as the exit pipe is no narower than 3" it shouldn't affect the mapping/power. Making it narrower to 2.5" would probably create some back pressure and affect mapping/power a bit.

I don't exactly know how having a very big outlet affects mapping but as far as i'm concerend it just makes a different noise and/or a lot of noise.

If the exhaust system was 2.5" right the way through to start with and you have a 2.5" outlet i don't think it would make any difference to mapping/power either.

Eddy may be right here in suggesting a 3" bung instead of your 2.5" bung. Others may disagree if they know different or better. Eddy is the exhaust expert here though.