Matthys333

iTrader: (5)

Ok, so my 90 GTUs is bidgeported with a very limited restriction 2.5" exhaust. I have a resonator and high flow muffler on it. Needless to say, it is EXTREMELY loud. I can't even think riding in it. So I ordered silencers to take away some of that unbearable loudness. And then I wondered about cutoffs for my exhaust for when I race. Now my question is, with my engine as it is, will cutoffs give more HP b/c of pretty much no restriction or will it hold me back b/c of no back pressure? Let me know what you think....

wankelme!

i think you just need a louder stereo...

ACE0000

You could try a dual exhaust maybe... and backpressure is never good for an engine it is all about exhaust velocity and matching the pulses from the engine correctly that is why certain width exhaust are optimal if they are too small the pulses are too condense and you get backpressure if they are too large then the pulses will be too slow and the airflow will not be optimized. But anyways I don't think I have a good answer to your question because I don't know how exhaust length effects exhaust velocity so much. But I have always heard good things about electronic cutoffs in the past but that was mostly with turbos. I know one guy who gained about 50whp on a Celica with a big turbo when he opened it, of course it wasn't just the cutout he also increased boost when he opened it, or maybe it was just the less restriction that upped the boost but either way.

FD3S_B00ST

iTrader: (20)

after gettin out the car if ur able to hear things around you your car isnt loud enough :]

mazdaracer78

i agree with ace for sure on back pressure vs. velocity of exhaust pulses. as far as restriction versus free flowing? na and turbo rotaries act quite differently when it comes to an exhaust setup. turbo rotaries respond far better to bigger exhaust diameter. as far as cutouts on rotaries there are 3 main things to consider. first, egt, meaning ideal exhaust gas temperature on a nonturbo rotary is in the ballpark range of 1500 degrees f. you must ask yourself one question with this... are electronic actuators designed to handle this repeatedly? secondly, cutouts are known to LEAK. not much, but enough to make it sound like you have an exhaust leak (when the cutout is closed). so if you run a cutout, plumb it near an exhaust tip. third, having a cutout may help your low to mid rpm range, but i doubt it would help you out much on high end. this is all the info i can give without knowing everything about your exhaust setup... i almost did cutouts myself 6 months ago...

ACE0000

That is kind of what I was thinking length of exhaust usually has a lot to do with torque vs peak power than anything else. I also forgot about how hot the rotary exhaust is, so I don't reallly know how well a cutout would work. I've also heard the thing about leaks but idk if you did it right you might be able to minimize that.

Matthys333

iTrader: (5)

I do have dual exhaust right now. They're duals with resonators and high flow mufflers. I understand the concepts of turbo's with cutouts and pressure inside of the exhaust. didn't know about the exhaust temps bein 1500 degrees tho. I just remember that the least amount of restriction for a bridgeport, the better. I just didn't know whether cutoffs would help b/c of absolutely no restriction

FC3Sdrift

iTrader: (5)

you would definately feel the differance with the cut outs in the higher rpm
would be deaf though

Matthys333

iTrader: (5)

Lol, so other than being deaf, would it be worth getting put on my exhaust?

ACE0000

Another thing to consider is how much hp is the high flow muffler actually getting you. On my Celica I was going for N/A power but I alwasy figured if it wasn't going to be a strictly race car I was going to keep a nice big muffler on it, I had a race header catless straight pipe with a magnaflow resonator and the TRD axleback which had a pretty big muffler. And it was never horribly loud, except in really high RPMs and I never got any tickets. I just figured the maybe 3 or 4 hp that removing the muffler, or putting a freer flowing muffler on would get me wasn't worth the loudness and getting tickets all the time. I've ridden in an Integra my friend had that was totally straight through no cat or muffler and I definitely think the raspyness and the fact that it's almost deafening at even low RPMs is not worth it at all.

So anyways, maybe if it is just a few hp just try to get a slightly more restrictive but quieter muffler(s).

Matthys333

iTrader: (5)

I'm not gunna pay about $100 for two new mufflers when I can use silencers on the ones I have on. Which takes away the annoying part of the exhaust. But my original question was will there be a noticible amount of HP gain with cutoffs on a bridgeported 13B

mazdaracer78

first, FC3Sdrift, if Matthys333 already has a high flowing exhaust, he will not notice any difference on the high end...

secondly, Matthys333, having a "bridge port" has nothing to do with the exhaust. it's the intake side that is bridged. if you have an exhaust port setup without the stock baffles, i feel your pain. my exhaust is also ungodly. if you can incorporate the apex'i ATS, (active tail system) it might not be a bad idea.

if you are not familiar with them, they are spring loaded tail inserts that open fully under high load. kind of like a vacuum actuated cutout, except the valve opens from back pressure.

Evil Aviator

The exhaust system on my car is fitted with slip joints and V-band clamps so I can quickly change the configuration. For example, attached are pictures of the quick-change test pipe and cat with welded-on V-band flanges.

FC3Sdrift

iTrader: (5)

with the higher rpm the amount of air the motor is displacing would make a differance with basically open headers but may have an effect on the bottom end

mazdaracer78

the issue is NOT about volume... IT'S ABOUT VELOCITY AND NOISE...

what happens at high end? velocity increases... when it comes to noise reduction, a good high flow monolithic catalytic converter has been known to help quite well...

unless you are running an air pump... in this case any cat will be suitable.