Mailing List Message #65395
From: Neil Unger <>
Subject: Re: [FlyRotary] Re: Mufflers
Date: Sun, 24 Nov 2019 16:26:58 +1100
To: Rotary motors in aircraft <>

Thanks Lynn, now makes sense,


On 11/24/2019 3:53 PM, lehanover wrote:
Sorry, I was referring to the earlier post of the pencil drawing of the perf tube with the down tube at the front rather than the rear of the muffler. The Borla was the same except huge and the 4 inch central perf tube was surrounded by six small perf tubes instead of any filler like fiberglass or Lava rock. Unaffected by heat. Lasted the last 10 years of racing. About 30 pounds. 4 inch central tube and you can see all the way through it. No baffles or obstructions. It was still in the car when sold a few years back. Later we shortened the right side
installation and rather than exit the rear of the car for left side sound equipment the exit was on the right side with a 90 degree down turn. That worked well until the 103 Db rules came out. Then we made it a straight open 4" tube with a rolled back end ring to reduce injured shins. Exhaust exited just ahead of the rear wheel.
Right side sound was all the way out the back with a 90 degree bend pointing to the left. 

Lynn E. Hanover

In a message dated 11/23/2019 3:50:00 PM Eastern Standard Time, writes:


                  The design seems to have been lost??  Can you repost please?


On 11/20/2019 10:29 AM, lehanover wrote:
This is a design that I think will be as close as any for muffling. I would keep the outlet to the rear end.
Years ago we took a new racer to Sebring for a first outing. The muffler was one of those big suit case looking things. It did work but the muffler was inside the car because of ground clearance. It overheated the driver. So as we went through the weekend were wrapped house insulation around that muffler. Then the muffler began swelling up and muffling less. Also the engine was popping about 3/4 of the straightaway. Another Rotary racer took pity on us beginners and demoed how our float bowl was totally empty by half track.  The needle seat was then metering the fuel and that was not nearly enough.
We changed our fuel pumps to series connection. That had us out of the tuning problem but still too close to best power. The muffler swelled up so as to look like a giant pillow. The insulation melted. The internal pieces
of muffler piled up in front of the muffler outlet and the driver pitted with about 20 HP to race on. We retired to Naples Florida. Found a man with a drill press. Bought  4" steel tube at NAPA and a house jack at Lowes. I built a muffler similar to this drawing. But straight through like a glass pack. Worked great. The next day we went to the false grid with high hopes. The car was stuck in first gear. We didn't start after towing to Florida from Ohio. I now live in Florida in winter. So we learned a lot. The muffler outlet must be big enough to allow any interior piece to fly off into space should it come loose.  Only stainless no carbon steel. Bigger holes near the front of the perforated  tub. this allows supersonic high pressure gas to get outside the tube and reenter through the smaller holes and slow the shock wave a bit. This is similar to the Mazda race muffler, but that thing is short and fat. Designed to fit under the rear bumper of an RX-2 or RX-3. That has an empty chamber in front of a perf tube style muffler, but there is no connection through that chamber. So, only sub sonic gas needs be dealt with. Those mufflers failed by being beat to death and falling off of the tail pipe. Another note: the most disagreeable part of the noise is in the center of the flow. I put a round piece of 1/4 steel in the center of a 4" tube and it did help. We had a 4" 90 degree tail piece. We could turn left or right. So as to aim it away from the sound equipment at each track. The Generation II (wedge shaped body) had a insert in the liner that helped very much on sound. Find one and see if it can be installed in the later housing. 

Lynn E. Hanover

In a message dated 11/19/2019 10:36:52 AM Eastern Standard Time, writes:

Here is the picture from Andrew's email. 

My exhaust is stupid loud. I've tried a few things which didn't work. Getting noise complaints around the airport while testing.

Just reading this Gary Schwarz's link, looks promising. Andrew, did you fit yours inside the cowl? I'm surprised 5mm endplates are holding up.

- Matt Boiteau

On 2019-11-19 12:57:36 AM, Andrew Martin <> wrote:

Kelly, I would if I had some, really did not expect it to work as I deviated from the design a bit. Will be back at airport on weekend to take photo, too late for construction photo. But nothing to it.

I read about the idea by Gary Schwarz in this thread, post #7 , post #58 for his testing and post #142 sums up his findings.
Someone on here may know him as he was doing it for a rotary. Mine is much shorter than his drawing below due to space constraints but the theory works.
edit: Ahh!!! deleted his picture as too big to post. it is in his post #7 mentioned above though.

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