If the newer "V" (Silver series 4.5 hp) engines and the previous "F" engines use the same rings, piston and con rod, how can the "V" series produce 1/2 more horsepower? If all "F" series engines are the same internally, how can some be rated for 4 hp and a few 5 hp?
Compression ratio will play into the mix too. 'Advertised' horsepower is higher than what the engine actually produces. Case in point, the Duraforce is listed at 6.5, when the repair manual says 4 or 4.5 hp.
The D-400 and D-600 engines have slightly lower compression ratios than the F engine.
