MACS muffler use

Stuka Stunt Main Forum · 12 of 12 known posts recovered

Dzlstunter · Mar 06, 2001 03:59 PM

LAST EDITED ON Mar-06-01 AT 04:00 PM (EST)

Several people report good results with these mufflers on stock OS40FPs or clones (running them pipe-style). Has anyone tried one on an engine which has been reworked by one of the "stunt engine gurus"? What should happen? What actually happens?

Steve Helmick · Mar 06, 2001 11:05 PM

#1 source

There is a thread about this subject at John Thompson's Yahoo CL Club Forum that answers most of your questions. You can link from Phil Brown's master list. Stock engines (i.e., with a fair amount of "blowdown")and with stock head shims seem to work best. Nils ran a Randy Smith tuned FP.40, but stock was better (more power). I think the best bet would be a Leonard tuned engine, as it retains most the blowdown, closer to stock timing. I don't know what Leonard does with the head, but that may need to be returned to stock. Nils says that the pipe actually seems to limit the peak rpm like a stunt pipe. I'm sending Leonard a set of plans soon and will slip a Mac's muffler in for testing if he promises to try it. Are you guys flying your Stukas yet, or is the snow still piled up? Steve

LNeumann · Mar 07, 2001 07:59 AM

#2 source

We haven't had snow for a long time, but now it is the windy season. Then follows the rainy season. Somewhere in between there, however, we start to fly. It is getting light earlier, now, and once it stays light long enough to go out in the evening we will start flying for real. (Evenings are usually a breeze, or, maybe, a lack of would be a better description.) So, send the muffler. We should be able to give it a shot shortly.

Leonard Neumann

Nils · Mar 07, 2001 11:57 AM

#3 source

Actually, when I first swapped out Scotts FP/pipe & put in my own it didn't have the power Scotts did. I asked Scott about it & he told me to pull the head off his & see what was in there for head shims. I pulled his head off (well, not HIS head, his FP's head

) & there were NO shims in there at all. I pulled the shim out of mine & it ran just like his. Btw, I run GMA Powermaster 10-22 in mine.
Since I hit the fencepost on takeoff with my Cardinal, I'll be flying the Oriental/FP.40 a lot for a while, at least until I get my Shark 45 finished :/
Nils

LNeumann · Mar 07, 2001 01:25 PM

#4 source

>Actually, when I first swapped out Scotts FP/pipe &
>put in my own it didn't have the power Scotts did.
>I asked Scott about it & he told me to pull the head
>off his & see what was in there for head shims. I
>pulled his head off & there were NO shims in there at all.
>I pulled the shim out of mine & >it ran just like his.
>Nils

This is NOTto be recommended!! A stock FP engine should have a deck height (top of piston to top of rim at top dead center) of .190 inches. The stock head has a depth, without head shims, of .190 inches. That gives the proper head chearance of .016 with the included head shim. But with no head shim, the clearance would then be zero!

Now, many engines will end up with a clearance of as much as .007 without a head shim, but that is only because of sloppy tolerances. If you have one that is "right on the money", the way the factory intended to make it, you will have problems galore! And even discounting the fact that the piston could be hitting the head every time it reaches the top--especially given a little expansion due to heat--when you are running 10% nitro on top of this you are inviting trouble.

Some engines, like the Magnum, for instance, use thinner gaskets, and may still have some built in clearance if the gaskets are removed, but all of the FP series of engines-- ALL of them--if built to specs, will have the piston hitting the head with no head gasket installed.

Just thought I might warn you. Those gaskets are there for a reason other than merely adjusting the compression on the engine.

Leonard Neumann

Steve Helmick · Mar 07, 2001 07:17 PM

#5 source

The interesting thing (to me) will be the prop that will work for the Stuka Stunt Werks tuned engine. Will it be a 12.5" x 4 Bolly 3 blade, the Tornado 10-4 three blade that Scott & Nils recommend, or a 12-6 BY&O? I suspect that the pipe will mandate less prop to get the rpm, which still isn't that high, around 10.5k at launch. As Leonard has promised to test the Mac's Muffler, I'll get one in the mail this week (I hope). Steve

Crapshoot · Mar 07, 2001 09:24 PM

#6 source

Purchased a Macs muffler a while back and finally decided to try it out today on a profile ship. Doggone! The fuselage mounted gear was right in the way of where the back of the muffler needed to go. Oh well. Have to put together something else that is more compatible. Hmmm, wonder how one of these would work on a Fox 35. Shouldn't be any worse than the stock unit. Any better possibly?

Nils · Mar 08, 2001 01:08 AM

#7 source

Wow Leonard! I flew my Oriental today & it was still working fine. It has well over 200 flights on it with this engine/pipe setup,(probably closer to 250 but I haven't gone back & added them all up). I went right out & pulled the head off of it when I read your post. Everything looks just fine in there, nothing hitting anything, no shiney spots on the piston or head. It's still on the same Thunderbolt plug I put in there when I put it together. Scott & I must have engines on the long end of the tolerance variation. Sometimes there's no substitute for dumb luck

Crapshoot- I had to use a 5/8" muffler extension to get gear clearance. I think I lost some RPMs doing that, because mine doesn't like to turn over 10K & Scotts will buzz up to 10,500 or 11K on his airplane (without the extension). It still has more poop than the Smith motor.

Nils

Randy · Mar 08, 2001 01:21 AM

#8 source

I've never tried one, but Nils has it right. I saw Scott run his and it seemed to have plenty of power. And pretty durable,too considering some of the screaming runs he had while he was getting the set up to work.

The Nobler he used the set up in when I saw it seemed to have plenty of power.

Randy

Steve Helmick · Mar 08, 2001 01:44 AM

#9 source

Wow, I didn't think about the muff hitting the LG. That's good to know, now I can engineer around that. Adding the exhaust spacer that Nils did adds volume and tuned length...do these changes move the rpm range up or down...what's the theory? All I remember is that the smaller stinger outlet increases the torque and makes the setup more docile for speed models. I'm still wondering about the overheating in cold weather. Increased baro pressure may suggest a need for less compression, cooler glowplug or less nitro? Any other ideas? Steve

LNeumann · Mar 08, 2001 07:25 AM

#10 source

In cooler weather either decrease compression or go to lower nitro. Just remember, the higher the nitro, the lower the compression (more head spacing). The lower the nitro, the higher the compression (less head spacing). Cooler temperatures and lower altitudes mean less nitro. In hot weather you can increase nitro to compensate for lost power. I typically set up the 35 FP conversions for 5% nitro which makes them a bit higher compression than some. And because I do use a head shim it is more tolerant to a range of altitude and temperature changes. The closer you have the head to the piston, the less tolerant it is going to be.

Also, any muffler (or pipe) will suffer with an extension. I have a feeling (we shall find out) that the "magic" in the Macs Muffler is not that it boosts power in pipe-like fashion, but that is is less restrictive than a lot of mufflers and simply doesn't kill off as much power. Most stock mufflers are notorious for losing power in an effort to quiet the engine. Or they get heavy. Have you checked the sound level on a db meter? I have one, so will, and will give you a comparison as to what I find. I'm curious.

Leonard Neumann

Scott Riese · Mar 26, 2001 11:23 AM

#11 source

HI GUY'S I've been down and out for awhile,So I think I should reply to this one. The mac's muffler works on all OS engines 20,25,35,40,46, and the ST-51 However it's the 40, and the 46LA that I worked hard to make them run. The fuel seemed to be the most important factor. They like sig 20-25% all castor and 10% nitro. I tryed more the six different types of fuel and found that keeping the rpm's steady sig worked the best. Bryon's all castor came in a close second. Rpm's for the engine(40os-fp)10,300 three blade grish 10x4 62 foot lines, thunderbolt plug. The OS46-LA had an extra .005 head gasket rpm's 10,300 with an APC 11.5x4 prop. I had this engine on my VEGUS and at 65oz It had the power. Same fuel.The ST-51 I'm still working on getting the right power curve on this one, I got the power BUT, I'm getting 6.0+ second laps and running out of time in doing the pattern. I had this engine in my 55oz Windy's Cardinal. But it's the 40 and the 46 that I know work and plenty of runs to back it up. Sorry that I've been gone but out of work and loseing most of everything to make ends meet ...it's been tough. SCOTT