The heat pipe idea has been brought up before. It sounds good in theory but so far no one has spent any time implementing the concept.
It has been mentioned a few times, I
brought it up in one of my first posts on HBA. I'll just say there was no applause. In theory it would be a good way to move heat from the exhaust side of the head to "somewhere else" (?) where it can be disposed of, but the practical considerations of doing that are significant.
There are other already proven methods to remove heat from the troublesome exhaust valve. Both Porsche and the motorcycle world have spent a lot of time on this air-cooled head problem. All we have to do is copy what they have done.
There are only 2 really good solutions to using the VW engine at higher power levels for aviation use:
A new purpose designed air-cooled casting that isn't constrained by the need to bolt onto a typical ground bound application.
A water-cooled head. This, IMHO, is the best solution but unfortunately it also requires air-frames that can be easily adapted or air-frames designed with water cooling as part of the original concept. Very few of of either exist.
I like the idea of better fins. I also think there may be some potential for
oil cooling (squirters for the underside of the pistons, channels in the heads, or at least fins in the rocker gallery and LOTS of oilflow to cool the head and valve stems).
On the VW the primary limit is the heat transfer from the exhaust valve. Solve that one and we may find another area to be the limit.
. . .
Increasing the power available from 60hp continuous/80hp takeoff to something like 80hp continuous/100hp takeoff means increasing the continuous heat rejection capacity by 33%.
My impression is that the max continuous HP of the present Type 1 VW aero engines is about 70 HP (assuming good baffling, reasonable OATs, etc). And, I suspect that's pretty close to the mechanical limit of the bearing saddles and the magnesium case itself, at least if we want the case to last more than a few hundred hours.
That
doesn't negate the value of a better head for aircraft use. Better cooling (fins, oil, or water) will keep the CHT cooler at that 70HP continuous output, which will increase the time between top overhauls and improve the inflight reliability of engines run at high power outputs. Also, better cooling will increase the time an engine can run at 80 HP or more before very high CHTs are reached. Smaller ports and valves with more meat between them will improve VE and reduce head cracking/maintenance.
The best "street" heads are pretty good right now, if the limitations are recognized and respected. A purpose-built head would give us more cushion. But, IMO, asking for significant additional continuous HP because we have more head cooling will just invite other problems and ill-placed gripes about the reliability/suitability of the base VW design for aircraft use. That's happened in the past.