I have a Knisely muffler. 3 years old, about 250 hours.

The flame cones are showing some warping, as viewed through the tailpipe. I've been told there is approval to remove the cones; as long as you have the external carb heat muff, which I do.

Does anyone know the reference for the flame cone removal approval(service letter, bulletin..)?
Can someone share their experience with this muffler configuration?

-Performance gain?
-Oil/cyl temp reduction in the summer, on floats?
-Cabin heat loss in the winter(avg temp here in winter is about 20F, but we do fly high on long trips, up there at 9-10k it can be down around 0F.) We do have backseaters normally.

Another option is an Acorn muffler, STC'd without the flame cones.

Thanks,
Aqua

Acorn Muffler -worth every dime-Exhaust system safety should be a priority. My 2 cents from someone who has been poisoned by carbon monoxide/leaky exhaust and survived.

I have the SB you're requesting. I'm not sure how to attach it to a post here. Send me an email and I'll send it to you.
RP
[email protected]

A gutted muffler will yield much less heat in the cabin, in my experience. You'd need to have your engine sitting on a dyno to see a performance gain, the amount is so small that it goes unnoticed. These things aren't too finely tuned to start with.

I know some IA's who will live by the service letter, others will make you buy a new muffler.

250 hours is pretty standard for a -520 if its getting leaned at all, I bet it's about right for your Ponk too.

Thanks all.

GB, understand on the cabin heat; do you have any experience with the gutted muffler's effect on oil and/or cyl temperature? To some degree; I'm challenged with cyl temp in the winter (cargo pod, skis), and oil temp in the summer (floats).

I have a Pponk in a 182 and a few years back the cone started to come apart so we cut it out. No noticiable difference with the exception being less heat in the cabin but still adaquate heat.

I have never operated Cessnas on floats, so I can't say for certain. I know lugging them around certainly adds a new twist to things. We never really saw any difference in CHT or oil temp on wheels, but we never had any of the accurate engine monitors like JPI etc. Of course it is hardly ever above 70 degrees here either.

Could be that you'd gain a few degrees to the good, doubtful it would be much though. If you can get away with a muff without the tubes and get enough cabin heat, then it's the way to go maintenance - wise. If they ain't there you don't have to fix them.

drp1 was kind enough to email me this service letter 63-11, and saved a $1200 new muffler when my annual turned up that my flame cone was missing. I figured I'd try posting it as an attachment here so that others can find it quickly in the future.