An RX-8 has quite a different exhaust configuration than an RX-7.

No RX-7 with straight pipes is ever quiet, unless it's turned off. Even then, the residual tinnitus is probably quite deafening.

As for the 'name-calling,' I didn't call him an *******. I told him not to be an *******. It's a critical difference.

 

I ran my IT-7 racecar with a 2.5" straight pipe in place of the muffler several times. That car had an stock port 12A, ISC header, long primaries into a 2.5 pipe over the axle. Normally I ran a lava rock packed dyno-max bullet muffler at the rear of the car.

The car would make the 103db SCCA sound spec with or without a muffler as long as I pointed the end of the exhaust away from the sound station. Other than being lighter than a muffler full of rocks, there was NO performance advantage seen using the straight pipe.

The last time I ran the straight pipe, a corner worker came up to me after the race, asked me if the yellow RX7 was mine. I told her yes, expecting her to compliment me for my mad racing skillz. Instead she slapped me and told me her ears were still buzzing! I put my muffler on for the next day.

 

One thing I did notice is that using mufflers with larger exit diameters tended to mellow out the exhaust tone a noticable amount. One of the best was a $50 straight through tuner muffler with a 2.5" inlet and a 4" exit. Looked loud but wasn't.

 

sound is a wave, anything you can do to make the wave smaller, will be quieter.

 

Just gonna throw out my little bit of rotary exhaust experience and share my current setup.

Having ran my stock port 12a with a short strait pipe and just driving around the block, it was
loud, louder than a street stocker with open long tubes. It was loud enough that 10min later, a
state trooper came rolling by looking for what made the ear splitting scream. I only did it once
and my ears rang for many hours after.

On the other hand, my current setup (on a street ported 12a), RB streetport headers, 2.5" piping,
Magnaflow presilencer and muffler, is loud but, not ear splitting. I can drive by cops and they don't
look at me any different than the turbo diesel with 4" stacks with no mufflers it sounds really good
and flows pretty well.

My honest recommendation is to AT LEAST run one good muffler if not a muffler and presilencer.
Ultimately it's your car and hearing, and like other folks have said it WILL be a cop magnet.

 

Haha haha, an open header rotary adventure is a must do just for the experience. It's defeaning, insanely loud and vibrates every sense in your brain and eye ***** at redline. People will notice you. Step on the gas and pedestrians 6 blocks ahead will stop and turn around just to see what the hell could possibly be making that kind of noise. Cruising next to people will get you the death stare, and passing people who have open windows at full throttle will probably make them swerve a little as they get a full taste of rotary loving.

There is no gentle cruising with a straight pipe/open header exhaust, it usually sounds terrible with a massive drone. It only sounds good when you're hammering on it, and it's kinda quiet on decel but that may just be a relative kind of thing. Do what makes you happy, have a good laugh doing it. Wear earplugs. Thin wall pipe will drive you nuts. Take videos please :-)

 

I might have a video when I thought that the turn around style muffler was robbing power in my setup. Road race header to an unknown silencer collected into some 2.5" pipe and straight out the back. It ended up being no different to the button dyno and sounded crappy so I put it back to the way it was setup by the previous owner. My favorite setup was selectmaz short primary headers with 2.25" piping after, I ran (2) 12" stainless steel packed silencers then up over the axle into a large body muffler with a fairly large tip. Best sounding setup I ever had.

 

Just curious but why don't you want to go over the rear axle? I just built a 3" over the axle pipe for my racecar. I had never done this before and was kind of dreading the project. But, it wasn't that bad to do at all and the finished product has have no clearance issues with the axle or the body of the car.

I used 3 mandrel bends - 2 90 degree pipes and 1 45 degree pipe - that I bought at a local stock car shop. Cost me $60 and about three hours fab time. 2.5" mandrel bends are readily available

 

Weight, ease of configuration, and no matter what going over the axle is going to sacrifice what could be potential HP gains.

This will take a while to bring to life but hang in there.

 

go under the axle, plenty of room... well until the exhaust heats up and starts melting, but i digress

 

Worrying about HP losses from the over-axle pipe is hilarious.

 

Sorry but I don't see a HP loss with going over the axles. The bends are not that extreme. Weight is negligible - 1.5 lbs tops. I have seen tube frame RX7 race cars with side exit exhausts but they also had a lava rock muffler that was bigger than a house to keep it quiet. And 103dbs ain't quiet.

Want to see pictures and videos of what you create.

 

I didn't know this was a debate topic!

I should just listen to what you guys say right?

Seriously, this is going to be an EXPERIMENT, I have no absolute rock solid set in stone ideas yet,

give me a break.

Again, not trying to sound rude.

Also I don't understand how over-axle piping would not impede HP gains. It's not really hilarious, it's bogus.

 

Just how big were those mufflers? Home made or off-the-shelf?

 

How do you plan to have the exhaust exit? I ran a flattened, rectangular section tip with an angle cut on a 4 cyl racecar once. It was about an inch high and close to a foot wide to maintain the correct cross section area. It attached to the inside wall of the sill with an isolator at the front and back. There's also a local guy with a V8 IROC-Z who runs a side exit on his track day car with a similar design. I rewelded mine once, then redesigned it due to cracking. He redesigned his twice for the same reason. They look cool, but they can be a bitch to get right.

Any expanse of flat, unsupported metal in an exhaust system tends to "ring" a lot. Better to avoid it if possible.

 

Op, just a thought but, have you done any reading into a true dual exhaust? If not it may be adaptable to your idea and it is know for great hp gains and you could run it like you want with 2 highflow glasspack style mufflers. I will still recommend trying out no muffler or open headers (basically the same) before you don't go with a muffler. It sounds cool but, can wake Martians, on Mars.

 

I definitely wanted to try true dual, it's still on the list, don't worry.

I thought glass pack mufflers were bad on rotary's due to the high heat?

 

Glass packs arent bad except it doesnt last long, say burnt out within a week.

 

I think the axle over piping idea, along with the collecting it just before the axle not "impeding hp gains" has more to do with the exhaust pulse theory and scavenging the rotors over with back pressure. It actually does help the engine spin, thus a hp increase.

If you just run straight pipe it has no restriction, but I did what youre doing now with dynomax ceramic turbo mufflers. It sounded horrible, didnt last long, and went slower than it does now with the Rb dual exhaust (which is over the axle)

 

It's a discussion forum. We're lending you our experiences and opinions.

If you don't like that, don't post a thread. Get a blog and turn of the comments.

 

back in the day, there used to be a race class called Pro7, which used a 1st gen Rx7, really popular class. engine was a stock 12A, stock intake, stock exhaust manifold. you had to run a 2.5" exhaust.

they played with all kinds of stuff and found that the over axle bit does take some hp, but its only like 3hp, so they just ran the thing under the axle, like i say tons of room.

is 3hp significant? for them 120hp was a front pack car, and 112hp was a back of the pack car, but for a street car, you need under 98db more than you need 3hp, and on a street car you can use a header, so you get to make more than they did.

 

Excellent post j9fd3s.

 

This is a discussion forum sure, but I'm starting to not see the discussion side of this thread any more, and it's more or less a try-and-prove-me-wrong thread at this point.

And it's not the point that it's only 3hp, it's the point that it does sacrifice hp. I don't care whether it does or doesn't, my point is that it genuinely in real life sacrifices HP which sure is insignificant, but 3hp is 3hp.

Idk what your problem with me is Moses, all your posts seem to be aggravated towards me. I'm obviously open for discussion, why else would I be here, the only thing you've done since you posted here is try and tell me what's right and wrong.

 

Type less, weld more. It's an exercise, so details aren't as important as action. Your first attempt will lead to the second, and you, as well as the peanut gallery, will benefit from your effort.
Have at it!

 

kinda seems like you already know exactly what you want to do, so let the "debate" die.

Just do your thing, and post your results.