What do you guys think would be the best engine for a diesel conversion in or around the 40 size,,as to weight,, power,,and effenciency,,i was thinking about buying an os 40,,,suggestions anyone????

Do yourself a favor and buy an engine that was built as a model diesel engine. Conversions work, but they rely on more ether than normal diesel fuel to make them run. Why? Because the converted engines do not have as much compression as the real thing. The result is that you are stuck with running high ether diesel fuel. The disadvantage? Ether evaporates and escapes the fuel very quickly. You can have a gallon of unusable diesel fuel in a hurry.

Also, the lower end of the real diesels has been built to take the stress. Converted glow engines have not. That's why they run lower compression.

Irvine makes/made a fantastic diesel .40 R/C engine.