Does a straight pipe on an N/A = Bad? Because I have a 3" cat back (with resonator) that I took off of my JDM FC turbo, and I want to put it onto my N/A FC. However, the previous owner did kind of a hack-assed 'dual' job from the header back, and I was just thinking of getting new piping welded in from there back to the cat back system. Will this totally rape me of low end torque (not that nearly stock N/A rotaries really have any anyways ) and pose any risk to the 5th and 6 ports with the lack of backpressure?

 

I have an RB header with a straight pipe replacing where the presilencer should go. I have stock y-pipe and stock factory mufflers. When I first did this, the noise doubled (since N/A's are so quiet stock, this means it wasnt really loud at all). BUT the flow destroyed my stock mufflers. Broke the welds. So I salvaged newer factory mufflers and so far so good.

If your using an stock header, I know a guy that runs an RB downpipe (off stock header) RB straight through presilencer with straight through magnaflows. Its only loud above 3000RPM and a noticing level. Its really screaming at 7000, but its pretty deicent down below 3000.


In answer to your question, now that I've re-read it, if your concern is your 5th and 6th ports, do the air-pump trick, provided you still have it. This was done on my car when I bought it as the main cat had been removed eons ago.

Low end is sacrificed when the exhaust is opened up, but I often dont find myself below 3000 RPM anyways.

 

Never noticed any low end loss personally but it was extremely loud so I ran a resonator and a straight through muffler with a removeable silencer. Definitely an increase in power at high rpm and the motor pulled right to 7200 instead of falling off around 6800. That was with my 86' na with a very mild street port and stock manifold to 2.5" exh. As for the 6 ports, you just have to find the right spot to connect the pipe to the exhaust and it works fine. Took me a couple trys though.

 

I have RB headers and pre-silecer on my s5 and it's great because an s5's actuators run off of the air pump. now, if you have an s4 the actuators run off the backpresure and i hear the RB system doesn't give enough back presure so i would think you would lose hp. so you might have to hook it up to your air pump if that is possible (i'm not sure).
so good luck with that and keep spinning.

 

my exhaust is 2.5" straight from the manifold to the Y pipe, then 2 cans. it's very loud. I dont drive it without the silencers in.
You're 5th and 6th ports probably wont open with a straight exhaust, I wouldent know.. I just removed my acutators and wired them open.

 

Thanx for all the feedback guys. I just talked to the previous owner, and he informed me that it already has a bracket installed to manually open/close the 5th and 6 ports for track days and such, so I guess I don't have to worry about the lack of backpressure anymore.