R975 Radial engines

[Bob Phillips]

Just a follow up on the discussion of suitable fuel grades for the 975. I have exchanged emails with retired engine builder and instructor Tom Henderson from down under. Tom owns and operates a beautifully restored C1 that he demonstrates at shows and events from time to time. He has been kind enough to respond in detail to a variety of newbie questions about fuels, oils, compression ratios and ring types and I really appreciate his patience! Tom tells me he is running 92 octane no alcohol fuel in his engine. He thinks this is a good compromise between lower alcohol infused fuels and higher aircraft oriented gas. While the dangers of using too low a grade of fuel in a higher compression engine are well known, there may also be consequences for running too high a grade as well. This may include elevated chamber temps and burnt valves for little gain in performance or economy. He also runs a semi synthetic 20-40 diesel oil which has better anti corrosion additives and detergents to try and offset corrosion in an engine that only runs occasionally. Cylinder temps (#1)! are about 400 degrees which are well within the acceptable range.
Another interesting thing Tom pointed out is that an aircraft engine runs a cam where there is higher cam lift and more overlap of valve opening, a cam which favors higher speed operation and which idles poorly, hence limiting their use in a land vehicle engine. Hmm, I wonder if I could get some -46 cams reground to C1-C4 specs? In this day and age it is unlikely that any of the 975 engines would get the abuse and hours of a vehicle actually involved in conflict. Hopefully with care and routine maintenance, a radial engine should run, for shows and events, for many years without major problems.