Mac muffler on Supertiger Bluehead
 

I have a 70's Supertigrr 60 Bluehead on an Aeromaster that I have restored. I installed a Mac's muffler on it. Today I test run the engine. After a 27 year layoff the Bluehead started on the first flip and sounded great. That is until I removed the glow driver. It died almost instantly. Assumed the old glow plug was bad so replaced it. It ran after removing the glow driver for a few seconds and then started going very rich. It was throwing a small amount of raw fuel out somewhere (I think the front bearing). It then died again. It seemed to be running hot even though it was very rich.
After messing with it for a while I decided to remove the Mac's muffler. It started running perfectly although very loud. I then decided to put the old Dubro baffle plate muffler I use to use on the engine in my Fliteglas P-51. Again it ran perfect. Removed Dubro muffler and re-installed Mac's muffler. Would not run or barely run very rich. Dubro back on and ran perfect again.
After looking at the Mac's muffler I believe that the opening for the muffler (where it attaches to the engine) is to small. It is about 75% the size of the engine exhaust opening.
I can only conclude that the Mac's muffler is causing to much back pressure for the engine to run correctly. Has anyone else ran into this problem? I guess I will try to increase the size of the muffler opening (not the exit but the opening that fits against the engine exhaust). I would like to use the Mac's muffler as the engine is fairly loud with the Dubro baffle plate muffler.
Thank you for any help,
Ralph White, Neoga, IL

RE: Mac muffler on Supertirge Bluehead
 

....make sure your fuel is fresh. The engine dying right after the glow driver is removed
is a classic example of bad fuel. ;)

FBD. :D

RE: Mac muffler on Supertirge Bluehead
 

Ralph,


What fuel are you trying to run this engine on?

It is a high compression engine and is designed to use 0-5% nitro; not like many current engine targeted for North America, that will run on 15% nitro.


This engine will simply not tolerate much nitro.


Also, there was more than one version of the Blue-Head ST; the earlier baffle-piston type and the Schnürle type.
The two can easily be distinguished by looking at the external design.

The older baffle-piston type also had a PDP version, which made as much power as the Schnürle type.
I believe there was also a two-plug version...

What type is yours?


As to the raw fuel leaking from the front (runny nose), it could be your crankshaft is highly corroded in the front-rotor area (under the carburettor), where it is supposed to seal.
Leaking there is a symptom; not the real problem.


As to your concern from the small entry hole to the Macs One-Piece (I presume)... have you seen how small the entry is to an UltraThrust tuned muffler, for an OS .40-.55?
I believe it is about half the area of the engine's exhaust stack.

Also, it will not affect the fuel pressure (causing a rich condition), since it is up-river from the muffler. What could affect fuel pressure is a small outlet hole from the muffler.

RE: Mac muffler on Supertirge Bluehead
 

I am running 10% nitro PowerMaster fuel. I believe I used 10% when I used the engine in the 70's.
I think my engine is the baffle piston type, probably PDP. How can one tell by looking at the outside of the engine. I purchased the engine around 1971 I think.
The engine went to a very rich condition even when I removed the muffler pressure tube. I still think the problem is the muffler because the engine runs fine with the Dubro baffle plate muffler. I may try a running 5% nitro to see what happens.
Ralph White, Neoga, IL

RE: Mac muffler on Supertirge Bluehead
 

Ralph,


You can tell if it is a PDP, by removing the head and looking down the cylinder, at the intake ports...

PDP ported engines have two narrow, angled Louvre ports cut in the sleeve, on the exhaust side of the piston-baffle.

These ports bring fresh, cool mixture into 'hell's kitchen'...

Through the exhaust these ports are probably not visible.


I don't seem to remember whether this engine does, or does not have sub-piston induction, which may cause reverberation of intake air, potentially causing more fuel to be taken by it, as it goes back and forth through the carburettor. But mere back-pressure with no sub-piston induction, will not cause the engine to run rich.


Take that chance to see if you got an extra head shim under the head (only one is standard - two is for 10% nitro).

RE: Mac muffler on Supertirge Bluehead
 

I have used a Macs muffler on an ST60 BH. He is correct about the excessive muffler pressure, it makes the mid range almost unusable. I bolted on a newer ST muffler and everything returned to normal(just a slightly rich midrange). Both mufflers made the same rpm with a 11-7 prop.

RE: Mac muffler on Supertirge Bluehead
 

Hi Kweasel, Which newer ST muffler did you end up using on your ST60 BH? Do you believe opening the inlet on the Mac's muffler to the size of the engine exhaust would solve the problem of excessive muffler pressure? I like the looks and design of the Mac's muffler and would like to get it to work.
Ralph White, Neoga, IL

RE: Mac muffler on Supertirge Bluehead
 

I recall that the Bluehead ran fine on 10% nitro. Some of the older engines did not like excessive backpressure. You may need an idle bar muffler even with the PDP and STS ported versions.

RE: Mac muffler on Supertirge Bluehead
 

Sport Pilot, Did you mean idle bar glow plug? If so, that is what I have in the engine, Fox long. If you meant idle bar muffler, I do not know what that is. I'm sure I use to run 10% nitro in the engine back in the 70's. The engine ran great back then and I think it is going to run fine with the Dubro baffle plate muffler. But the Dubro muffler is so loud.
Thanks, Ralph White

RE: Mac muffler on Supertirge Bluehead
 

Yes, I mean't to say an idle bar plug.

RE: Mac muffler on Supertirge Bluehead
 

The Macs muffler can be drilled for less back pressure but it will get louder.

RE: Mac muffler on Supertirge Bluehead
 

Well !!! After changing glow plugs (now have a Sonic-Tonic plug) and getting the low and high needles close to being correct, I have had several good engine runs (and flights) on the Bluehead in my Aeromaster. I have been using the old Dubro baffle plate muffler. Of course it is to loud for today's standards.
Today I put the Mac's back on without changing anything else. The first thing that happened was the engine ran very rich and died. I removed the tank pressure tube from the muffler and the engine started running correctly after a minor needle adjustment. However, the RPM dropped from about 12000 to barely over 10000. (Running a Top Flite 12x6 and using an old Heathkit thumb tack, so not to accurate). I than put the pressure tube back on and turned the high needle down until the engine started running right. The needle felt like it was all the way closed or very close to it. The engine ran fine when I flew the Aeromaster but it just couldn't hack it at only 10000 RPM. So I put the Durbro back on.
When I got home I drilled out the outlet hole on the Mac's muffler as much as possible. Also the interior hole on the baffle tube. It just about doubled the area of the outlet hole, maybe more than doubled. I am now ready to try the muffler on the engine again to see if the RPM gets close to the 12000 I was getting with the Durbro muffler.
I'll let you know as soon as I get a chance to run it, probably in a couple of days.
Ralph White, Neoga, IL

RE: Mac muffler on Supertirge Bluehead
 

A Mac's muffler will produce about twice the muffler pressure (18") than standard mufflers (9") for .45 engines. Drilling out the tailpipe and the internal baffle will reduce the pressure to approximately that of a standard muffler. It stands to reason that greater muffler pressure would make the high speed needle more sensitive. I drilled mine to 11/32". The noise level did not go up much.

Bill

RE: Mac muffler on Supertirge Bluehead
 

My experience with three different Macs one piece mufflers is that they are more restrictive with more back pressure than the stock mufflers

RE: Mac muffler on Supertirge Bluehead
 

Thanks Bill, I just measured mine. I opened it to 15/32". About as big as possible. Hope the noise doesn't go up too much. Did you notice an improvement in RPM? What RPM are you turning? What prop?
Ralph White, Neoga, IL

RE: Mac muffler on Supertirge Bluehead
 

Thanks for the input w8ye. I agree that they are more restrictive than stock mufflers. I'm having trouble finding a satisfactory muffler for the Supertigre 60 Bluehead.
Ralph White, Neoga, IL

RE: Mac muffler on Supertiger Bluehead
 

Today I tried the Mac's muffler with the exit opened to 15/32". First I ran and flew the Supertigre Bluehead with the Dubro baffle plate muffler. Ran and flew very well. The engine turned 12000 RPM with a Zinger 12x6 prop. Then I put the Mac's muffler on. The engine would only run 10500 RPM with the opened up Mac muffler. About 500 RPM more than the stock size exit opening. When I flew the Aeromaster with the Mac's muffler on there was a difinate lost in flight performance due to the lower RPM. I have currently given up on trying to make the Mac's muffler work on this engine. Some day I hope to try a new Supertigre 60 muffler on the Bluehead but that is going to have to wait. I'm tired on messing with mufflers and want to get some flying in. I will have to put up with the little bit of extra noise of the Dubro muffler.
Ralph White, Neoga, IL

RE: Mac muffler on Supertiger Bluehead
 

Ralph,


Please note that this 1,500 RPM loss amounts to no less than a 33% HP loss.

It is a much greater loss than it seems.