Best exhaust setup for 88 FC S4 NA
 

Have a non turbo S4 6 Port and from what I understand you need the back pressure in the exhaust to open the 5th and 6th port

so my question is what is best exhaust setup while keeping enough back pressure for the 5th and 6th ports

if you tee a boost/pressure gauge into the 6 port hose, you can see backpressure. it needs to be around 2.75psi. i was able to do that with the stock exhaust!

my street exhaust recipe is the stock manifold into the downpipe of your choice, RB makes a nice one https://www.racingbeat.com/RX7-1986-...rs/S16206.html
into either a cat of your choice, or the presilencer https://www.racingbeat.com/RX7-1986-...ers/16206.html
and then into the cat back of your choice

I have found good working order using a Bonez single cat pipe coupled to a Borla stainless system. .. .1986 non turbo 5 speed.

The pressure feed back to the ports happens on the last cat

https://cimg6.ibsrv.net/gimg/www.rx7...d1ec3ffa28.jpg
California car using 3 cat setup being replaced by a single cat Bonez system available from rx7.com

I added a type k tc and a O2 sensor port.

Racing Beat long headers and there silencer with stock mufflers works great. I can watch the vacuumed ports kick in as I rev up the engine in neutral. Also sounds great. Engine is street ported.