I always thought I was running one until I stuck my head under my car (yes a rare occurance!) at the weekend and saw that my centre section has a bit of a bulge in it, which I assume is a resonator?

My car is decat with a sports cat downpipe, and the centre section which is now in question, is the resonator just to reduce noise or does it effect power as well?
what gains if any could I get with a straight through centre section?

 

What car, year, exhaust etc? I have 2 resonators in my decat exhaust and my brother(Spec C) has a straight through pipe, his is much, much louder and made no gains over mine that were worth the headache, beleive me!

 

oops sorry, I drive a my05WRX, decat uppipe, prodrive cat downpipe, decat pipe, 'centre section' in question ?!, RCM backbox, engine has an STI intercooler, 550's, vf35, walbro fuel pump and a map to around 330/340bhp

thanks
Iain