Hi I have just fitted a new preformance rear box to my 96 wrx. But when I take it for a spin the power seems to be down than when the original was on. The system is standard apart from the rear box. I am not sure of the make but its just the right sound and has a 3.5" tailpipe. I have orderd a middle decat pipe. Is this normal when fitting just a back box.

 

I fitted a Tiphoon in place of my Magnex 6x4 oval and the power seemed well down at low revs but a bit more grunt at higher revs. It also seemed to spool up a bit later, about 3.2k rpms instead of 2.8/2.9k rpms.

I've now put an H&S 3.5" on and it's back to its previous performance characteristics.



(MY01 WRX, HKS panel filter, H&S backbox, straight through centre, Walbro fuel pump, ecutek remap).