OK so i have about 10-15 flights on my big pink that flys OK with my ryobi 31 and a 16X12 apc but today one of my muffler bolts came lose allowing my muffler to swing to the side and run open head wow!!!! what a difference that thing was screaming how bad is it to run muffler-less? when i landed she wasn't that hot. but i also know back pressure comes into play so how can i keep her ruining that good without hurting her ? i have a stock muffler with the guts taken out.

If you don't have problems with noise you can run them open exhaust.

I get awesome (non-restrictive) performance from the wackerengines mufflers.

Backpressure isn't really needed with the pumped carb motors....

I fly an 18x8 on my Ryobis.

Good Luck!
CrazyHerb

thanks for the info herb tanks also for the time you have spent on the net setting up your site i built a big pink and love it the thing flys great esp with the muffler off i will get some Pict's of my plane on here asap so you can check out my rendition of big pink. thanks again you rock!!!!

I drill the heads of the bolts and wire them together with safety wire..........
or hasn't come loose yet..........

I would be curious to know the RPM difference with and without muffler.

Bill

Macs makes an exhaust pipe for them that turns towards the top of the head and then exits towards the rear. It must have been intended for boats?

Enjoy,

Jim

I had the same problem. it would get loose up in the air, but it would misfire so bad because of exhaust fumes being pick up by the carb, what I did is to gut-out the inside of the muffler or drill the inside plate looking from the exhaust inlet with several 3/8" holes and some in the bottom at the exit, or grind out the sides of the muffler take everything out then weld it back together you will notice a big increase in power, also install the gasket that goes in between the muffler and the engine to alleviate some of the vibration effects and put some red locktite on the threads if the threads are stripped go ahead and re-tap them with a 1/4" 20 or 24 tap and also use red locktite(you can also use the blue stuff) those are the things that really took care of my muffler getting loose problem. good luck.
Bill Pomplun A.K.A. Aero Nut.