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Post  Iceberg on Tue Aug 11, 2020 4:59 pm

We all know the muffler sounds cool but power is down with it. No mystery. Maybe Sunday flier where houses are nearby it would be appreciated. I prefer to hand launch my planes and the muffler needs to be on a plane that is taking off with landing gear to allow slooooooow speed pick up.

However does anyone have access to actual data of the real RPM loss with a muffler? I would have thought the muffler would get red hot but you can still touch it after a run. Well I can but my fingers are like crocodile claws now. However it is not too hot.

So RPM loss on a given motor?

Just for curiosity sake.

Thanks
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Post  Cribbs74 on Tue Aug 11, 2020 5:47 pm

A lot of variables. What cylinder are you using? The #6 cylinder was designed for use with a muffler, but there are other non-SPI cylinders that could work. That coupled with a #1702 head will get you close to where you were at pre muffler installation.

Do you have a tach? The best way to tell for your particular engine, fuel and environment would be to tach it with muffler on and with muffler off.
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Post  Iceberg on Wed Aug 12, 2020 12:17 am

Hi Cribbs
Thanks yes I have a tach. I could of course test them. I was just curious to see if there might be some recorded data regarding performance reduction or combo that is already in print about the use or not of mufflers.

So if you used an SPI cylinder with a muffler what might be the effect I wonder?

Thanks
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Post  Basswood on Wed Aug 12, 2020 2:14 am

Ive also had good high rpm in tests with the factory RC cylinder muffler/throttle control if you shim up the cylinder and add a high compression head to eliminate most of the SPI..
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Post  Iceberg on Wed Aug 12, 2020 9:49 am

Hi Bob
Interesting. So by shimming the cylinder up to just cover the SPI it can run pretty good then. It isn't bad to have the mosquito sound if the muffler is on as long as we can keep performance up.

Thank you
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Post  Ken Cook on Wed Aug 12, 2020 2:17 pm

Define what performance your looking for. I have at least 6 Cox QZ's from the 60's. I don't use any of them with the mufflers. The QZ has a dual bypass, and a high comp head. Using a stock 325 head the engine offers turd like performance.  With the muffler and 35% nitro it makes as much power as a strong Babe Bee which is pretty poor in my opinion.  It's certainly not Black Widow performance from any of them. These have the mill finish aluminum muffler with the hex base and the spring clip that rotates around it's circumference. It's a pain in the rear to start with the clip blocking the exhaust port, with the clip open it still offers enough noise to be problematic. There's a shim under the cylinder which lifts it up enough to block the SPI. As mentioned it came with a high comp head. Using higher nitro really jeopardizes the plugs and they're certainly not getting cheaper.  In my honest opinion, if your in search of a muffled .049, Cox products are not the avenue to go down. A Norvel .049 using 10% nitro offers much more power and a more pleasurable exhaust note.
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