Running a MACS muffler on my ST .51

[Andrew Borgogna]

I finally got my Score into the air a couple of weeks back for some initial trim flights.  Following a couple of weeks back East for business I hope to continue the trim process this coming weekend.  Anyway what I wanted to ask has anybody else tried this muffler from MACS Mufflers?  While flying on the dark side I use their mufflers and tuned pipe equipment for many years.  I like their service and quality, they really are easy people to work with.  To make a long story short when I decided to go with the ST .51 I knew the ST muffler had to go so I went to MACS and looked at their selection for the .51.  I found the following muffler, and so far it has work well, but I must add that the engine is not completely broken in and I and still getting familiar with the engine.  One thing I noticed was I have to set the engine wet on the ground, it unloads in the air but then runs a consistent 2 cycle for the rest of the flight.  I did not notice any 4-2-4 break and no real run away.  Just a consistent 2 cycle with a nice blue smoke trail from the pipe.

[Dan McEntee]

  Hi Andy;
    I have read of guys using tha MACS pipes on FP.40's and such with good results. I see no reason they won't work with the ST.51. I have extensive experience with the ST.51 and have used tube type mufflers for the most part, and the engine doesn't have a very big break, maybe more like a wet2 to a peak2 is the way I can describe it. The engine is pretty forgiving once you get used to it. Try adding or taking out head shims in you trimming process.
   If there is one thing I don't like about the MACS pipe just from looking at it how it sticks out a lot from the engine for how long it iis. Have you weighed one yet? I'm curious about their weight. I must admit I had considered this once briefly, but like I said was mainly turned off by the size.
    Good luck with the trimming process and please keep us posted on your progress.
   Type at you later,
   Dan McEntee

[Joe Messinger]

I have a Macs Mufflers on a OS LA .46 and  I'm happy with it.  I can't say that it enhances performance any but it doesn't hurt it either.  It's as quiet as the stock LA muffler and the information that I have says it weighs 2.2 oz.  It is rather long and I had to bend the landing gear a bit on the Cardinal so the muffler wouldn't hit it.

I'm pretty sure the Macs Muffler I have on the LA .46 would be the same size as one for a ST .51.

As is the case with everything, I have heard others say they didn't like Macs mufflers.  I have read here on Stunt Hanger claims that they do enhance the performance of some engines like OS FPs and that these mufflers have some of the characteristics of a tuned pipe.

Joe

[Andrew Borgogna]

Thanks guys for the replies.  I did put mine on the scale when I first got it but I really don't remember how much it weighed.  I do remember it was less than half the weight of the stock muffler.  Yes it does stick out a bit, that is probably the biggest negative but on the Score it's no problem because it is on the side of the plane.  Except it exits exhaust about an inch from the leading edge of the wing.  Makes for a lot of clean up.  The way it was described as a fast 2-cycle and slow 2-cycle is kind of how I would describe the ST .51 as well and not very much difference between them.  Like I said I am just starting and will let you know how things work out.

[Joe Messinger]

Andrew,

You can add a extension to your muffler.  They curve downward which should divert most of the exhaust & residue.  The extensions are made of silicone, are very heat resistant and can be easily trimmed to a desired length.  In some cases, the extensions might restrict the flow of exhaust gasses and cause overheating but I have used them on several of my engines (one being a ST .51 with a Big Art's muffler on my Score) with good results.

Regards,

Joe

[Steve Helmick]

The MACS Muffler, being a tuned pipe (1/4 wave, somebody says), won't appreciate the silicon angled extension at all. You can gently bend the stinger a bit, so maybe you can get a little more clearance, or get all the oil onto one side of the wing.

I had a MACS on my .46LA powered Humongus, and liked it a lot. It takes the right prop, to get the launch rpm into the right range, which will probably be 10k+.  You'll need it to peak about 1,000 rpm over your launch rpm, or it will sag in the overheads. I'd expect a stock G.51 CL to want to launch in that 10k+ rpm range anyway, so it might work fine with the right prop. Maybe the 12.25 x 3.75 or 12-4 APC, or something of that sort. Don't be afraid to experiment. You WILL need a tachometer for this setup.  Steve