Camshaft Design & Profile Generation Software
ENGINE MODELING & CAMSHAFT DESIGN SOFTWARE
Duration is not Determined by Displacement and/or Peak HP RPM
(We are assuming the correct port and valve area requirements have been met and there are no other restrictions in the intake or exhaust tracks.)
The variation of profiles with the same .050” duration values is infinite and cannot be used to describe or clarify a specific profile requirement. The valve seat duration begins when the valve leaves the seat and ends when it returns. It is the total time between valve opening and closing. Determining the correct duration from the engine's cylinder volume, or engine displacement is not mathematically correct. Displacement is determined by the bore and stroke. Assuming the correct port area to piston disc area relationship, bore has no effect on cam duration. By itself, stroke does not affect the duration requirements either. But using the stroke and peak HP RPM values we calculate the mean piston velocity FPM, which is the average speed of the piston and one of the two determining factors of cam seat duration. The second determining factor is the mean port velocity, which is the average speed of the inlet charge that will be filling the cylinder.