Hello,

Anyone have experience/opinions with or about Mac's Mufflers?

I got one of their tube mufflers for my OS LAS .46 awhile back but have not yet had a chance to try out the combination on a plane.  It will go a Cardinal. As is most often the case, some say they don't like them but never explain why.

This thing is big (8" long) but relatively light in weight.  I have run the engine with the muffler on a test stand and didn't notice any problems.  Pretty quiet.

Any input appreciated.

Thanks,

Joe

Actually, any tuned pipe "rattles" when it's working right. If it's a carbon pipe and enclosed, you might not be able to hear it. It sounds like the wheels are about to fall off...not a big deal, if the wheels aren't falling off. 
I used a MACS Muffler on my .46LA powered Humongus OTS, and will use the same engine and pipe on a 4Runner pretty shortly. Nice setup, great fuel economy, and about as simple to run as a McCoy .35.  The muffler makes a wonderful handle for carrying your model, if you allow it to cool down!

Your setup should include a .285 venturi, ST type NV assy., stock compression, 10-22 Powermaster or equivalent, Thunderbolt long idle bar glowplug. A 4 oz tank should be plenty if the engine is broken in, but if not, it may not be enough. A 6 oz clunk tank would be good, with a fixed uniflow vent (metal tube inside the tank, rotate the tube or cork to adjust tank height). Don't use muffler pressure, and don't use a gasket. Lap the exhaust stack flat and smooth, and same for the muffler. A light smear of real silicon gasket maker might help, but I don't recall ever using it. You can tweek the stinger a little to get a little more clearance on the Humongus or similar. Don't put on a "rubber ducky"! You can also drill out the stinger a little, and pickup some power, but I never found the need.

The secret to the MACS Muffler is propping it right. It needs to run at 10,000 to 10,500, and at that, it needs to be rich enough so that it won't sag in the overheads, where you need max power. The 11.5 x 4 APC is a great match...maybe you can improve on it, but it won't be easy. The 12.25 x 3.75 APC can work, if you cut it down to about 11.5", but I can't say it's really better. A reworked 12-4 Pro Zinger would be worth a try. The same setup for a .40LA, but use the 10.5 x 4.5.  Steve

I used one on a TT36 on a Cartier Zlin. It was one of the best set ups that I'd ever ran. 11/4 prop, powermaster 10/22. Needle was broad and I actually think fuel economy was not compromised.
Yes it has a tinny rattle when it's running, you get used to it and after awhile you don't pay attention to it.
Dennis