Dyno with two mufflers?

[Scooter]

Has anyone dyno'ed their RX-7 with the TWO mufflers installed that are necessary to meet a 92db sound limit?

Cuz I just did. Let's compare.

[VinnyV81]

I wasn't aware that two mufflers were required? It would be interesting to know what a stock 6 port motor will dyno though...

[lateapex911]

I don't think he's saying that they are required by rules, I think he's saying that he tried two less restrictive mufflers in an attempt to get under sound regs rather than one more restrictive, (but quieter) muffler.

The cost vs benefit ratio is weight vs hp.

So, what are the conclusions?

[racingralph]

the 2 mufflers isn't just to be quieter.the 1st one, after the header,is really an explansion chamber (kinda like a 2 cycle). the 2nd muffler tones the sound down.the right combo....makes more horse power. contact mike at isc , the guys at speed source or steve e. these guys can build/sell this exhaust systems. hope this helps. ralph

[mustanghammer]

I'd check with Mazdatrix. I have seen their EP RX7's at the Runoffs with two mufflers so that they could meet sound at their home tracks. They were fast with and without the extra mufflers

www.mazdatrix.com (http://www.mazdatrix.com)

[Scooter]

So I have a full-dual exhaust that runs two pipes all the way out with two mufflers, one at each end. (And an expansion chamber in the middle of each pipe.)

It's quiet enough to be under 92db at the track. (The quietest limit so far around here.) Plus, since the mufflers are at the ends and they only service one rotor apiece, they don't seem to die.

A lot of people run a single, 3" pipe setup with a muffler in the middle instead of an expansion chamber, and with another muffler at the end. These systems seem to be quite enough for 92db, I think, but they also eat mufflers from heat.

If you don't run a second muffler in the middle of the exhaust, you will probably run about 98-100 db from what I understand. But I would love to hear from someone who dyno'ed a single pipe exhaust with both mufflers in place. A single-muffler exhaust making 100db does me NO good since I can't race like that at my home tracks.

[Scooter]

To reply to my own query, the Mazdatrix/Racing beat style exhaust with two pipes all the way back doesn't hold a candle hp-wise to the single 3" with two mufflers inlne.

Cuz I switched and while I haven't dyno'ed them back-to-back it's obviously faster now. (I can't say exactly how much because I made other changes as well.)

[racingralph]

here in the southeat us rx-7 guys share info about what we've learn to make our cars faster ....even helpin each other at the track ! you will need to keep the front muffler fresh.(about 4/8 hp off when it burns out) i'm going to change to a repackable bullet type muffler next. i think this will be the trick ! lets keep these "old" cars out front !! hope this helps .. racing ralph

[Scooter]

Thanks Ralph!

I have a Racing Beat pre-silencer on there in the middle. Hopefully this will last longer than your average muffler? Does anyone know this for sure?

[NCRX7RACER]

The racing beat presilencer should last for years. I have had one last for 10 years + on a street driven car.

[itsrx7inAK]

We had a 22 inch long cherry bomb in the middle and a corkport muffler at the end.....75% of the paint has burned off the the "midpipe" muffler and i'm sure all the fiberglass has melted and gone....based on how the volume increased over the weekend. I thought the tires were going to be the first to be replaced:shrug: