I need opinions on my exhaust. I run a RB header, dual pre-scilencer center section to dual 2.25" bends over the axel back to a 3" Supertrapp w/ two 12-packs of discs on the end. It breaths well and sounds........weelllll....LOUD AS HELL!! But I like loud...I also like quicker better. I've been told by "professionals" (R.B., M-TRIX, RTRY PWR) that I'm stupid for running it that way and I'm sacrificing h.p. My theory is that by keeping the exhaust pulses apart for as long as they could be, it would increase the scavaging effect and still flow fine with 3" inner and a 2 pack of discs. I'm at a point where I could change the actual end but I need other points of view before I committ one way or another.

 

I think the RB Streetport exhaust collects just before the axle. That'd be a good spot, IMHO.

My exhaust collects right at the header, so I don't have any practical knowledge on the subject, but my understanding is that, up to a point, the further out you collect the pipes, the higher peak HP, but at the sacrifice of low end grunt.

 

from my understanding each exhaust pulse is 67 inches long and if the exhausts are kept seprate fro linger than that there will be no scavaging and you will lose power. i recomend merging the two pipes at 67" or less into a 2.5" pipe then do whatever you want with it.. route it over the axel and put muffler of your choice on it. and from what I've heard supertrapp is not a good muffler for rotaries...

 

Hi,

A little experience from my setup. Back in 1989 when I was a kid freshly out of highschool. I worked hard to get this setup. The car was a 1979 Rx-7 with a Rotary Reliability and Racing street port motor, mikuni carb, borg and beck double disc clutch with the drag flywheel. I had a custom exhaust built, it consisted of a racing beat road race header (the header that doesn't collect at all) going all the way to the back of the car into two separate super trapp mufflers with the disc configuration setup for torq. I never compared the cars performance to an exhaust that was collected, but I can tell you this much, the car went like a bat out of hell. Raced a mustang 5.0, MR-2, mustang 5.0 convertable, vette, porsche 911 on the highway, buick grand national from a rolling start, he complained and said his turbo lagged. These where the many that fell to my car back in the old days. Don't know if that exhaust made me loose horses and if it did man I can't believe it could of gone faster that it did.
I don't have the car anymore, but I was thinking of bringing back that setup since thats what I knew worked well for me. By the way the exhaust sound was not tinny. It was a low v-8 type sound and of course loud :-)

 

Sell the Supertrapp and put that money towards a sack of potatoes. Once you've removed the Supertrapp, stick a potato in the end of the exhaust. The car will be much quieter, and you'll probably pick up a few horsepower. Replace potatoes as necessary.

No, I'm not really kidding. Dyno sheets that prove once and for all that Supertrapp blows nuts forthcoming...

 

Supertrapp is good for catching blown apex seals.

 

RB's exhaust system that collects at the rear axle i believe are smaller in diameter than 2.5 inch. remember that each exhaust pulse is a certain volume, and the larger the pipe, the shorter the distance it goes at a slower speed, whereas a smaller pipe will make the same volume go farther\faster. Just think about pouring a gallon of water into a coffee can or into a 5 gallon bucket. One fills up faster/higher, the other slower/lower.

dennis

 

Can you provide a link, this is very interesting and I'd like to read more on it.

thanks

 

For those asking about the dyno sheets - don't have them yet. Dyno testing on my car with the ST will be today or next week, and I'll be giddy with excitement to provide them.

 

ok so from what i've collected 2.25 with the collecter aprox 60 some odd inches away from the header would b ideal? just a question though, what are clutchpack's in a exhaust? never really heard of that till 2day

 

friends and i have found that supertrapps definately aren't for rotarys. if u like a moderately loud rotary exhaust and still produces good power, i have found that using the road race header with long primaries collected just before the axle to a single pipe over axle into i think it was '81 stock muffler(which ever year that had the least restrictive muffler), and if it's streetported, it REALLY makes a nice sound. find a muffler shop that'll let u experiment with different setups at a reasonable price on their labor.

 

My current setup is like this (front to back)

Racing beat short header
Presilencer
Cutout
Moroso spiral flow resonator
Magnaflow muffler

I was pleasantly suprised that I didn't lose much power with the Moroso muffler, and with the cutout, the thing WAILS!!!! Oh, and it's got a really nice tone when driving too.. lol

Dan

 

I'm building a rotary powered kit car. I'm going to be running a street port 12A with a 48 dco weber. My primaries will be about 36" before they have to be collected into the muffler. I'm more interested in improving torque than hp. What dia pipe should i run for the primaries?