ST Diesel conversion
 

I am considering buying a used Davis head for ST.40-.51's. Does the "kit" only include the head? How do these engines cold start? I have considerable knowledge of Diesels but I realize that these conversions must still not compare to larger engines in compression, fuel used, and method of ignition timing. Obviously a ST .40 is not capable of the 22 or 25:1 compression ratios I am used to. By memory I think the minimum I have ever seen in a "full size" application was 18:1. Are the model Diesel fuels of a high enough Cetane to start and run by "low compression" alone? If I did make a successful conversion of a ST .40 what kind of performance should I expect at about 4500' above sea level?

Thanks in advance. Take care, Cliff

RE: ST Diesel conversion
 

Model diesels are not really diesel engines, but rather compression detonation engines. Model diesel fuel runs aroud 30-45% ether. Compression ratios on 40 size diesels are about the same as 40-size glow engines. In fact a 40-size glow engine will run fine on diesel fuel once it warms up. I would think an ST 40 dieselized would swing an 12 x 6 prop better than 10,000 RPM.

Jim

RE: ST Diesel conversion
 

Cliff, one of the great things about the Davis heads is that normally you don't have to change the compression setting unless there is a huge change in ambien temp. My ST .51 conversion turns a 12x6 at 10,500. The Diesels are most effecient if you prop them for 8,000 to 8,500 rpm. Your .40 should turn a 12x6 three blade in that range.

RE: ST Diesel conversion
 

my st40 if memory serves me 8900 -9000 12x6 wood zinger apc plastic props
will turn a little faster at least 300rpm. also use an electric starter when warm
will hand start.any overcompression on a hand start is a finger wack.