I've got an 88 se and I took my car to the local performance exhaust shop so they could put on my new racing beat mufflers, and also put some high flow cats on. good thing i didn't order the entire cat back system because when they lifted up the car we noticed that there is a brand new Y pipe on there (bonus round). So anyway, the dudes at the shop suggested only switching one of the cats to high flow, because of the whole back-pressure activated aux ports (which i was impressed they new about). what do you guys think? will one high flow and RB mufflers leave me with enough back pressure? and how can i check to see if my aux ports are opening without taking it to a dyno and looking at them while someone else does a pull?

 

the stock hedders have enough backpressure i think. if u have a catat all tho it will have more than enough. but keep 2 muflers man the car just looks bad w/ one it doesnt look as ballanced. it was designed for 2 so... keep 2.

 

the 6th/5th ports on the S4's are activated by the amount of back pressure produced. there is a simple and cheap fix which is to simply hook it up to the air pump. then you go ahead and get the Racing Beat Headers and Prescilencer if you want.

 

I can tell you this- with a Bonez hi-flow cat (now gutted-don't ask), and the Racing Beat cat-back sytem, the aux ports WOULD NOT open when they were supposed to...A simple line rerouting to the air pump to ACV hose yielded more than enough pressure- I actually had to "tone it down" some 'cause they were opening at 3,000...But they work great now, and are solely dependant on engine rpm now, not backpressure...