Do RCS/ZDZ engines run hot?

I've been wondering about the Weed Eater conversions as I get closer to building/buying my first gasser.
Every gas engine that I have seen run on a plane seems cool to the touch after running.
I've seen 2 ryobi's, a Zenoah, and 1 US Engines.
Only the Zenoah was "not" in a cowl.

Normaly on my Weed Eaters (the ones I use to actually trim the grass ) the head gets too hot to touch.

So, when I first looked at RCS' web site, I noticed that the cooling fins are considerably smaller than most Weedy's and the Zen's and US E's. Pics of other popular RC designed gas engines seem to follow the "large fin" area scheme.

I'm betting that RCS runs hotter than a Ryobi, but how much hotter?