Heat Muffs

I'm getting ready to order the finishing kit, but trying to get some questions answered about which engine I want, in particular the heating capability as I live in the Northern States.

I am looking at an IO-320 horizontal induction because I think the cowling looks 'cleaner' I had a respected building expert point out that there may not be enough room to put 2 heat muffs on the exhaust system with horizontal induction, and that 1 muff may not be enough to keep the cockpit comfortable.

I have looked online and it seems like all the posts talking about heating cabins are several years old. Knowing that products change over the years, I'm looking for a more 'current' opinion.

I have seen this from Spruce https://www.aircraftspruce.com/catalog/eppages/turboheat05-15249.php.

I have seen some comment that state additional techniques are to not restrict the airflow in the muff as recommended and people using steal wool inside the muff to add in the transfer of heat to the air.

Any thoughts, ideas, advice?

Thank you for the comments, and Happy Thanksgiving!

Dave, I live in Rochester MN, just south of you. I suggest you talk to Vetterman about his trombone exhaust system. I don?t know if he makes one for the 320 engine. My RV-7A has the IO-360 with horizontal induction. When I ordered my exhaust from him, and told him where I was from, he insisted on putting two mufflers on the exhaust (not heat muffs). I have one of them routed to the normal place into the cockpit. I routed the other one up higher just under the panel on the right hand side.

I can?t say there is considerable fitting room under the cowling, but there is sufficient room. There were a couple of places where there was slight rubbing during engine start and we needed to do some tweaking of the Hardware on the exhaust to provide a bit of a clearance.

We have flown in weather well below zero here in Minnesota often (especially during phase 1). Not once have we had to apply full heat to stay comfortable. I did have to add a line to my landing checklist to turn on our seat heaters, since pulling back power for landing also reduces the heat that comes in from the mufflers.

Talk to Vetterman. He will steer you right!

I have the vetterman muffler system as well. I am only pulling cabin heat off of one. Even at altutude with surface temps at freezing, I barely crack the heat open.

I have a horizontal intake 360 and the Vetterman exhaust without muffler because the muffler system was not offered at the time. Stock design includes a single muff on cylinder 1. It is anemic.

I have added a second muff on cyl 4 in series with cyl 1 and take heater intake air through the oil cooler now. This has made the system acceptable for mid atlantic flying but i doubt it would be satisfacory for the snow belt.

This is not an issue of cabin air leakage. I did all the seal tricks during construction.

In my view it is a matter of heat balance. My observation is that the systems that work well are associated with muffs that have multiple cylinders pushing heat through them.

On a related note. I find that it matters how one runs the engine on cold days. I will run higher rpm which raises all the engine temps. Oil, cht and egt. The heater works better doing so.