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The 100HP VW--Reliable? Practical?

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Vigilant1

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Given the dearth of affordable 100HP engines, I'm reviewing the approaches to obtaining 100HP from the Type 1 VW for limited periods (takeoff and 5 minutes of climb). What I've seen or what seems possible:
-- PSRU: By allowing a higher engine speed while keeping prop speeds reasonable, these appear to give good results in draggier airplanes (105 HP for about 5 minutes). I'm not quite understanding why the same setup wouldn't work just as well with cleaner airplanes if the right prop were selected. After all, the RPM and torque are close to an 0-200, and these have worked will on slippery planes.
-- Smaller prop: Allows higher engine RPMs before the tips reach critical mach. While this might allow the engine to make more HP, the higher profile drag from all the "junk" in the way of a small prop (esp the fuselage), as well as the lower efficiencies due to higher disk loading, make this fairly unattractive.
-- Turbo: Not widely done in airplanes, but Revmaster sold a turbonormalized setup for their 2100 engine version for many years (along with an available two-position prop). A nice by-product of a turbo used to get 100HP at SL would be this ability to maintain a constant 75 HP or so at 8000 ft MSL.
-- Nitrous oxide injection: I know cars have used it and I'm aware of at least one seaplane that has used NO boost to get off the water. Simple, relatively cheap, and would seem to involve about the same engine stresses as turbocharging.

Anything I'm missing?

Limits on all of the above come from the ability of the little VW engine to shed waste heat. A short-duration run gets around this by just using the heat capacity of the engine and oil--things get hotter and hotter, and you need to back of at 5 minutes or you'll break something (exhaust valve stems, valve seats, etc).
Ways to increase the available higher HP running time (or reduce thermal stress on the engine within that 5 minute run time):
-- Run rich (use the excess fuel to cool things off). It probably works okay to keep head temps lower. Simple, cheap. Diluton of oil with fuel likely to increase wear.
-- More oil, increase size of oil cooler. Limited impact on cooling the critical valves and valve seats.
-- Improved heat transport from fins: From what I've read, the "Fat Fin" heads have done a good job of making practical, sustained 75HP operations possible. But even with this, the guys in the know aren't suggesting that 100 HP ops can be conducted for more than about 5 minutes. Nikasil cylinders also provide slightly improved heat transport. I wonder if still higher heat rejection can be accomplished:
--- Copper brazed to the fins?
--- Water jacket attached to the fin tips
--- External water spray to incoming cooling air (even a gallon of water requires a tremndous amount of heat to convert from liquid to vapor)
--- Heat-pipe to carry heat from the spark-plug holes to a remote location, etc).

Again, are there other approaches that might help keep temps in check, at least for a limited time? Ideas, other installed approaches, etc are welcome.
 
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