Straight-pipe exhaust on NA FC?
 

I got my FC a few months ago and am planning on getting a full exhaust system by the end of the summer once I save up enough money. The factory mufflers on it have leaks due to rust and road debris (thus making my car sound like crap). I want to remove the mufflers and temporarily install some regular 2"-3" straight pipes in place of them, basically just to see how it would sound and if I notice any differences in driving it... So my question is, is this a bad idea or do I have nothing to worry about (other than possibly annoying the sound police)? I'm only just beggining to learn more about the Wankel engine and I'm not aware if they run on back pressure like certain 4 cylinders do. I wanted to ask for advice on this forum before I do anything to my car that I may later regret. Thanks.

the 5/6th ports rely on backpressure to open up so if you open the exhaust enough the 5/6th ports will not function properly. You could always wire them open but this will cause you to lose some power in the lower end.

these cars are pretty loud, its quite amazing actually. Iv heard the reason for it being so loud is because the exhaust port opens so fast, actually causing a sonic boom because the exhaust comes out so fast. And if thats not loud enough, the afterfires (everyone here wrongly calls it a 'backfire' which means somthing totaly different and is devastating to your engine) when the unburnt fuel gets ignighted in the exhaust sounds like a gun firing. I'v raced my car with an open exhaust, and the report off the exhaust is truly somthing to behold. I dont know if a stright muffler will be enough. It might be if you still got your cats.

Well, it depends on if you have an s4 or s5. If you have an s4, your 5th and 6th ports are opened by exhaust backpressure, so with straight pipes you wont have enough backpressure and your car will actually be much slower. On an s5, the ports dont open from backpressure. Like the others said though, it will be AMAZINGLY loud. N/A FC's especially are some very very loud cars. I have straight pipes (no cats or presilencers) back to dual GReddy mufflers, and its still one of the loudest cars I have ever heard even with the mufflers. Sounds very nice, but VERY loud.

I've actually run holey mufflers vs. open, and at first (holey mufflers, header, no cat) I said to myself "Jesus, that's loud."

And then I ran it open. And then I put the holey mufflers back on. Trust me, aside from permanent hearing loss, even Italian traffic cops would pull you over with an unmuffled rotary.

So in short, I second the "don't run it open" general voice here.

Agreed!

more accurately the aux ports on the 84-88 non turbo 13B uses exhaust pressure, rather than back pressure.

Thanks for the advice. I guess I will keep it how it is, for now.

So If I do a custom exhaust on a s4 the pipe cant be too big even if i have mufler and cat

?????????????????????

so i guess nobody knows.....

You could probably just buy the cat-replacement from RB and downpipe, and then go with a straight pipe after that. That should keep enough backpressure to open your ports.

????

what are you saying???

Are you asking if you can get too big of an exhaust pipe??? yes of course you can and your performance will radically suffer if you do.

See there is a careful mix of big enough, but not too big so that exhaust volocity increases, but does not waffle around in too big of a pipe.

I assumed it was S4 due to his profile but thanks for correcting my mistake. You really don't miss anything do you ;)

The o2 sensor is in the stock exhaust manifold so if you're straight piping from there back then nothing. It stays put. The Racing Beat Headers have a spot for it in the collector or the rear rotor pipe depending on the header( street or road race). I think the cheap OBX's on Ebay have a spot for it as well. Now the tube is a different story. If S5 you can toss it as it's not needed without the cat. If S4 the pipe feeds exhaust pressure back up to the 5th and 6th port actuators. Here is a post I made on the subject years ago that explains a little.

"On a n/a you'll want some sort of pre-silencer or muffler somewhere before the main mufflers at the rear to help cut the noise down. As to the tube for the auxportactivation on a S4. The Racing Beat pre-silencer for the 86-88 cars have it, the universal ones do not. Also you could make your own tube but you can't just drill a hole and weld a tube to it. This is why I believe some after market exhaust doesn't work with the actuators. It's not backpressure it's the tube setup. Their( RB) tube bends 90 degrees once in the exhaust path so the opening of the tube is directly in the exhaust flow. Seems they are using the exhaust pressure to open them, not backpressure.

S5 uses the air pump as previously stated."

Like I said it depends on the series of car you have. S5('89-'92) nothing it's not needed. On S4( 86-'88) the pipe feeds exhaust pressure back up to the 5th and 6th port actuators. Unless you buy the Racing Beat pre-silencer that has the tube integrated into it you're 'gonna have to get creative with what you do with that tube in order to maintain the functionality of your aux ports.