size of an engine

[raytam]

How is the size of the engine calculated? I know bore vs stroke, but is the stroke measured from the total travel of the piston from the total length of the stroke from the absolute bottom of the stroke to the top of the stroke? OR from the distance from where all ports (specifically the exhaust port since that is the first and last port to open/close)are closed?

I'm asking that because...if someone increases exhaust duration by using a dremel to cut the top of the port (to increase duration) without modifying the head button to compensate for removal of port material, I'm assuming that 1) you would loose compression and 2) you decrease engine capacity.

I am just curious since there are SO many opinions about modifying motors.

Thanks for reading.

Ron

 

[tnrcboatracer]

Stroke is the distance from TDC to BDC. It does not take into account the ports. Thus the displacement does not take into account the trapped volume, only the theoretical maximum volume.

 

[BB Mods's]

Bore x Stroke is the correct way, we only care about how much the piston moves, not the extra area above the piston.

if you cut the sleeve to raise the exh timing, you don't have to cut the head button lower, that's only the case when you shim the sleeve to raise exh timing.