Hi
I have a Tower Hobbies Kaos 60 with a OS 65ax and would like to fit a Jett Muffler.
Can anyone tell me a good prop to use with this combination?
Any change from a #8 plug?
Is an extra head shim required?
Fuel I am using is 10% nitro 18% oil (Klotz super techniplate)
Geoff

Hi Geoff,
The Jett muffler/mini pipe has an optimum RPM range. I will suggest starting with a 12 x 7 (I prefer APC props). You might try sending an email to Dub Jett, too. He can probably give you some specific recommendations. You should not need a head shim, the OS #8 is the correct plug and the fuel mix sounds good.
good luck,
will

Hi Will
Thanks for the reply much appreciated. Will try your suggestion after I get a few runs on the motor with the standard muffler as at present it has only had a couple of starts.
Have also ordered a s/s bearing from Boca as I believe the 65ax can have problems with bearings when running a tuned muffler.

Geoff

Hi Geoff,
I wanted to add that I am running an OS 65AX in a Sebart Mythos 50 (I don’t know what the ‘50’ means because the correct glow power is in the 65 to 80 range) set up on an old Hanno red pipe. I’m running a 14x6 APC with just about unlimited vertical and surprising horizontal speed. I originally planned to put a YS 80FZ in it, but it would have required significant modification to the cowl. I would say the 65AX in this set-up produces comparable power to the venerable Hanno Special. The Jett ‘muffler’ is really a mini pipe and will definitely provide a noticeable power boost. My only 2 ‘complaints’ with the Jett muffler are that it puts more weight in the nose of the airplane and you have to tune the engine to the mini pipe by finding the best prop combination of engine performance and airplane performance. Jett mufflers have, historically, been designed for high rpms, but since the AX series of engines are designed to produce peak power at a lower rpm range, perhaps the Jett muffler has been designed with this in mind.
Since this was a classic pattern question, what airplane have you built?
Regards,
will

At present I have a retrimmed Tower Hobbies Kaos 60. But am looking at a couple of options Blue Angle, UFO of Phoenix 7.
Also looking at getting an HP 61 pipe from Mecoa if the Jett muffler does not work out.
Geoff

Well i guess I have answered my own question. APC 11x7 prop with the jett muffler and 1/2" spacer block. Performance is like night and day compared to the OS muffler. Pulls through large diameter loops with out slowing and up lines are perfect now.

Hows the noise with that Jett muffler vs. the original?

carl

The jett muffler /exhaust may not be the best option for noise sensitive flying fields.
Defiantly higher noise level over the stock OS muffler.
Geoff