Fox Eagle IV .60 engine
 

Running a Fox Eagle IV .60 engine, current production;
Using a Zinger 11x7 Prop I ran the Stock muffler, the Fox Quiet Muffler and the Performance Specialties (AKA Nelson) Ultrathrust muffler on the New Eagle IV .60 engine. With the stock OEM muffler it runs around 11,500 rpms or so. With the Fox Quiet Muffler it runs better still with a little over 13,000 RPMs rpms so it has maybe a little bit of a tuned pipe effect.
But with the Performance Specialties UltraThrust muffler you can get it to peak out a little over 14,500 rpms but I backed it off as I didn't want to hold it there for too long with a new engine. But it is still new and may do even better with more time on it.

I ran my old Eagle III with the Ultrathrust muffler and got it to peak out at a little over 14,000 rpms too.
Going over 14,000 RPMs exceeds the design specs for the .61 size Ultrathrust muffler. The instructions say the .61 muffler is tuned for the 11,000 to 14,000 rpms range.

Running the Eagle IV 60 engine with the Ultrathrust muffler video clip:
[youtube]http://www.youtube.com/watch?v=qOeTpYEouiU[/youtube]


Fox Eagle IV with Ultathrust muffler: I fabricated a bridge adapter to adapt a OS 61SF sized muffler to fit the Fox engine.
http://i248.photobucket.com/albums/g...Muffler_01.jpg


Fox Eagle IV .60 engine tachometer reading using the Ultrathrust Muffler:
http://i248.photobucket.com/albums/g...Muffler_02.jpg

Fox Stock muffler on the Fox Eagle IV .60 engine
http://i248.photobucket.com/albums/g...Muffler_02.jpg

Fox Eagle IV .60 engine the the Fox Quiet Muffler.
http://i248.photobucket.com/albums/g...Muffler_01.jpg

Running the older Fox Eagle III .60 engine with a Ultrathrust muffler:
http://i248.photobucket.com/albums/g...Muffler_02.jpg

Fox Eagle III tach reading:
http://i248.photobucket.com/albums/g...Muffler_01.jpg

RE: Fox Eagle IV .60 engine
 

Is the Fox Quite Muffler quiter than the Ultrathrust muffler?  If so any ideas what is inside?  Might be able to make one from a stock Fox muffler.

RE: Fox Eagle IV .60 engine
 

You know, I have forgotten what was inside. I have vague memories of it being more like a Mousse Can type of muffler. The idea being to cool the exhaust gasses down before the gasses exit, which results in the small exhaust outlet as the exhaust gasses have cooled down some by the time the reach the outlet. The inner tube is smaller in diameter than the outer tube.

The two mufflers seem to be about the same for noise output, but that is mainly because of the propeller making most of the noise then at the higher RPMs. You can get the tuned pipe howl like propeller noise using both mufflers on the engines. One of these days I need to get a DB meter so I can check noise levels of things better.

RE: Fox Eagle IV .60 engine
 

if you ever run it with an apc 11x7 i would love to know the numbers your get. back in the 70s and early 80s the std prop for a 60 sized engine was an 11x7

RE: Fox Eagle IV .60 engine
 

I'll do that the next time I hook it up.
I was using Zinger 11x7's or Top Flight or Rev-Up props, all 11x7's at the time.
So I chose a Zinger 11x7 as that was what I was using back then most of the time.
We didn't trust plastic props yet. everyone was afraid of a blade letting go back then.
I think the problem is with a plastic prop, if you dinged the prop while the engine was running, it doesn't show any obvious damage, but a wood prop breaks immediately on the slightest ding. So with the plastic prop, it might fail because of internal damage you can't see.

I'll have to look in my box of props, I am not sure I have a APC 11x7 or not, I might have to buy one.

I actually have a old 20 some odd year old Zinger wood prop and when I tried it as compared to a new Zinger prop, they were still turning around the same RPMs on the same engine with the same fuel.

RE: Fox Eagle IV .60 engine
 

sounds good.... i ran my gold head"special edition" OS FSR 61 today and got about 13600(slightly rich)(11x7 apc) on 15% with a Jett 7.5" exhaust with a bridge adapter similar to yours... it was new in box till a few months ago and is swill breaking in