exhaust wrap question

[WesRagle]

Guys,

One more point about ceramic coatings. Don't forget to have the area clearly noted and masked if you intend to have a heat muff on the pipe.

Wes

[pilotyoung]

I read the above thread with great interest. I am a new to all this since I bought my Onex flying and did not build it. What is the purpose of the wrap? Is it to lower the amount of heat inside the cowling? One person mentioned lower head temperatures?

I am currently in the middle of a top overhaul. I have cylinders being delivered next week and then I will have everything to put the AeroVee engine back together. I have new heads, new cylinder kits, etc. One of the heads cracked presumably because of excess heat. So if I can reduce the CHT's I am all for it.

Thanks.

[WesRagle]

HI John Y.,

I think reducing temps in the lower cowl area (without reducing cylinder head cooling) is a good thing for many reasons. Having said that, I don't know if wrapping/coating the pipes has a significant effect on CHTs.

A little off topic but ... I think the only reasons for high cylinder head temps on a Onex are poor fuel distribution, poor baffling, or too restrictive of a cowl outlet. The nose of the cowl is wide open and air-speeds are more than adequate to cool the engine (assuming a reasonable climb speed).

Most of us have a good baffle seal, I assume your carb is set up properly, and the nose is wide open by design, that only leaves the outlet as something that we can modified to affect cooling.

If you have watched the Onex throughout it's development, the prototype flew with a small outlet and no lip. The plans were released with a rather smallish outlet with a lip. The plans were later revised to increase the size of the outlet and lip. As for my Onex, a custom engine installation required a large outlet for the induction system to clear the cowl. At present my cruise CHTs are right around 300 Deg. Due to poor fuel distribution one rogue cylinder is cruising at 330. That with the CHT probes as close to the plug as I could get them. Last Winter my CHTs were down around 260 and I was concerned that was too low. I asked the engine builder and his unqualified answer was "Cooler is better".

I've seen guys make a mess of their baffling chasing every little bitty leak with a tube of red RTV with little or no affect. Again, the outlet is the easiest place to look for improved cylinder cooling.

YMMV,

Wes