Heater Vent Valve

[rvbuilder2002]

Originally Posted by Carl Froehlich

Scott,

While some constant heat muff airflow is nice to prolong the life of the attached SCAT hose, I do not believe the heat muff itself is going to melt without cooling air. The heat muffs I use are made of Stainless Steel, just like the exhaust pipes. For that matter since I believe no one mounts heat muff at the cylinder exhaust port, the exhaust pipe temperature at the heat muff is much lower than at the exhaust port.

So as all things go, there are extremes that bound the problem. No heatmuff flow is probable not good for the SCAT hose. Too much heatmuff flow is a waste of engine cooling air - and for that matter not a great way to heat the cabin. Heat to the cabin is a function of pounds mass of air and temperature. The more airflow, the less temperature rise across the heat muff. Those interested students out there can take the data then do the equations to find the airflow that transfers the most heat to the cabin.

As I previously posted, a 3/4? orifice to reduce the heat muff airflow in the RV-10 still provides far more cabin heat that I?ll ever use. For the RV-8A single heat muff install, I increased the heat transfer area in the muff to get the added cabin heat - as well as reduce the airflow though the muff (less pounds mass of air but higher temp rise across the muff). 900+ hours in the RV-8A install and all is well. I?ll do the same for the new RV-8 project.

Carl

I have little concern for the SCAT hose and not much for the muff because there is generally airflow over the exterior surfaces.
For the same reason that Larry Vetterman has always told people to not use insulating wrap on his exhaust systems, I am most concerned for excessive temp of the pipe itself, being insulated by the muff and static air on the inside.
Particularly on a muff mounted near the fwd (hottest) end of the pipe.

[rv9av8tr]

Scott?s point is it?s important to allow cooling air flow over the exhaust pipe which is enclosed by the heat muff.

[ChiefPilot]

Originally Posted by rv9av8tr

Scott?s point is it?s important to allow cooling air flow over the exhaust pipe which is enclosed by the heat muff.

I think his point is that it depends on where the muff is. The muffs on the lower portion of the Vetterman crossover exhaust are fine after almost 900 hours as are the pipes. This is on an IO360, fwiw. The vans exhaust with the muff up front might be a different thing given its proximity to the exhaust ports.