I was given a plane that has an older ASP 1.20 2 stroke. I was test running the engine and it ran real nice and smooth however, the muffler seemed way to small for a 1.20. I checked out the muffler part number on line and discovered it's for an OS 60. So my question is how bad is it to run the engine with a muffle made for 1/2 its displacement. I was thinking of opening the muffler port to at least match the engine exhaust..

I am not even sure how well the plane will fly since it a scratch build, so I don't want to dump a lot of time into it until I can test it out in the air.

Thoughts appreciated!

Dave

what up dave? if anything it's gonna cause a lot more back pressure. 2 stroke mufflers are designed to be expansion chambers to allow the exhaust pulse to aid in the combustion process . but it don't take a genius to see that a stock 2stk muffler has a lot more internal volume when compared to a performance pipe like a mac's pipe for instance or for instance a pitt's or bisson style muffler.

probably best to slap a 16x6 apc prop on it and either tie down the tail or mount the engine on a test stand and 'safely' test it before chancing the airframe to an untimely demise. luck, and blue skies brother

The engine will work OK with the smaller muffler, but you may be losing some power that way. We used to run much worse mufflers than that on engines years ago. The engines weren't the worse for it, even though they lost some power doing it. The smaller muffler may be a blessing of sorts in disguise too. ASP tends to put carburetors on the engines that have too large of a intake venturi bore on them. That results in poor fuel draw and more dependence on muffler pressure to compensate for the lack of fuel draw ability. Thus the smaller muffler would increase the muffler pressure a little more and it may help. Heck the original owner may have had that problem too and went with the smaller muffler.

Since you test ran the engine already and it worked fine for you, then go ahead and use it like that. You can likely find a new 1.20 muffler someplace, but if the smaller muffler works, I would not put much effort into it.

Thanks for the replies. I flew the plane this week end and it ran well, seemed to have good pull, idled nicely. On the second flight one of the muffler screws backed out and my muffler was hanging on by a thread, no pun. I flew for about another minute before landing, engine did not dead stick. If it has a larger carb I would expect it to dead stick!

Dave

What's that old saying ? Ohhhhhhhhhhhhhhh yes, now I remember .

IF ITS NOT BROKE, DON'T FIX IT !!!!!

What I do is run the engine on the ground for a few minutes to heat it up good. Then stop the engine and retighten the muffler screws while it is hot. That usually keeps the screws tight then. What happens is the screws get hot and grow in length a tiny bit and that is enough for them to get loose.

Sounds like you got the right muffler regardless of make.

I think I will convert to a Beer Can Muffler. Cheap to make and it get my exhuast past wing.

A .60 size muffler on a 1.20? Hardly the 'right' muffler for the job, though it will work. It will just limit power; probably moreso on larger props spinning slower.