Port Speed Calculations
Port Speed Calculations
(OP)
I would like to calculate the port speed in an engine at different rpms. I am aware of the equation (bore*bore/port dia*port dia)*mean piston speed. However when I use this I get port speeds of 162m/s @ 7000rpm which seems way too high. The results from the equation seem incorrect, but is there a better equation or should i reduce the above by a % as per expected VE?





RE: Port Speed Calculations
RE: Port Speed Calculations
RE: Port Speed Calculations
A better equation is the inlet mach index, but that is also just a rule of thumb.
RE: Port Speed Calculations
Runner velocity = (piston velocity x piston area) / inlet runner area
RE: Port Speed Calculations
Whether you use mean piston velocity or peak, the equation is the same. In either case, you have to know what a reasonable value is. I think more information is available in the literature that is based on the mean velocity. Several magazines like Circle Track have suggested typical port velocities, and at least one SAE paper has covered the inlet mach index.
What you use also depends on what you are trying to accomplish. Do you want to rough in the valve and port sizes for a new design, or compare the ports in different engines? If so, the simple rule of thumb equations will work. However, if you are looking for results that are accurate to within a few percent, then you need to use a simulation that takes into account wave mechanics and all the other variables.
RE: Port Speed Calculations
RE: Port Speed Calculations
You would have to decide what port area you want to use- such as port area minus stem area, area through the seat, area under the seat, or just valve head area- and then do it the same for each engine.
RE: Port Speed Calculations
RE: Port Speed Calculations