Unseen24-7

I would like to replace the section of exhaust on my s4 n/a from the header to the y pipe, with a simple straight pipe. I would weld a bung for the aux ports to keep them active.

Would there be a significant drop in backpressure, so much so that performace would be comprimised rather than improved?

staticguitar313

iTrader: (2)

a straight pipe wont create enough backpressure to make the ports function, only open exhaust known to keep the auz ports functional is the s4 RB header with the special tube built in:

alexdimen

iTrader: (13)

I want...

alexdimen

iTrader: (13)

Oh, btw there is also a racing beat main cat replacement that still activates the aux ports.

Airceo13

or u can rig something up to run ur aux ports from teh air pump

Red'vert

Good S4 6PI thread:

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/need-help-auxillary-ports-551120/

Unseen24-7

What if I put a resonator (or some type of muffler) in the straight pipe, would this make enough backpressure/exhaust velocity/whatever to activate the ports??

Red'vert

It needs to be done right to both maintain proper exhaust back-pressure for an even powerband and also provide the 2 PSI pressure at the right RPM for proper 6PI actuation.

There are ways to electro-pneumatically activate the 6PI as well but the RB S4 header or RB S4 presilencer with pickup tube, (at least when used with their downpipes), are properly tuned.

Kryoung7

B S4 presilencer with pickup tube, with their downpipes - works great on my '91 vert; has 234,935 miles!

Unseen24-7

I was just reading in another thread where a guy knocked out the first 2 (pre)cats but kept the third (main), and this still (supposedly) opened the ports.

Oh yeah and which header is this(see pic)? Is this the RB true dual header that requires the presilencer, or some other RB header? I searched around on their site but i couldn't find this particular one.