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The Instantaneous IMEP method has been used to measure piston and ring assembly friction in a production Chevrolet 1.8 litre L-4 and a 5 litre V-8 engine modified for single-cylinder operation. Friction measurements are reported at different loads and speeds up to 1640 RPM under firing and motoring conditions with various oils and before and after break-in of the oil ring. Oils used were SAE viscosity grades 30, 50 and 30 with a friction modifier. Differences were found between motoring and firing friction, especially on the power and exhaust strokes. These differences diminished at higher speeds and lower loads where lubrication was more hydrodynamic. Differences in response to viscosity and friction modifier changes were noted between the two engines.

Typically, engines with relatively few cylinders have required higher cranking speed to start in low temperature ambients. Of the several factors that contribute to cold startability, this study has focused on the instantaneous speed variation of the engine during cranking. This theoretical computer study revealed that engines slow substantially during compression and that the lengthening of compression time is exaggerated as the number of cylinders is reduced. It is hypothesized that long compression time creates excessive heat and blowby losses. In turn these produce low compression temperatures and pressures, hence greater difficulty in igniting the charge especially under cold cranking conditions were average engine speed is low, By matching the compression times of various engines designs, the relative average speeds required to start can be predicted with reasonable accuracy.