I would like to remove my main cat but would like to keep the exhaust as quiet as it is now. If I install a muffler can I leave the air pipe to the main cat unpluged or do I have to block it off completely or paritially to allow the aux ports to operate normally. This is an 88 NA convertible.

 

dude it much esier just to leave the cat on. you wont get in trobble for emmisions and by leaving the cat on you will get enough backpressure to open the ports http://www.rx7.com/store/rx7/fcexhaust.html go there and get a highflow cat has just the right amount of backpressure and you will still pas emissions.

 

Just use a presilncer from racing beat, that will provide nice flow and enough back presure to open your ports.

 

i thought s5's used back presure to open ports not s4's

 

you got that backwards

 

Definitely backwards.

And that cat doesnt eat as much preformance as you think it does, just keep it on.

The RB presilencer is not made to fit with the stock manifold, you must buy the RB downpipe with it, or RB headers.