Airspeed through minimum cross section

[superbike]

Hi all

I remember GC helping me with an airspeed calculation based on bore/stroke rod lengh and minimum cross section of the splitter section of my port.
I have seen some calculators for this but really i would like to use the GC methord. Can i ask what it is ?

GC quotes

So, what about your Mach index? The controlling section in a head like yours with 2 inlet valves per cylinder may be the splitter regions or the curtain area under the valve (throat diameter x Pi x lift). A detailed study of both areas especially the curtain area change as lift increases determines the controlling section at any given time in the intake event. Your maximum instantaneous piston velocity is at around 80 deg after tdc and using my method of ratio bore to minimum intake area (in your case the combined splitter area) to simulate pressure ratio effect between bore and port and taking:

bore 100mm
stroke 61.5mm
rod length 124mm
Mach = 354.8m/s at 40 deg C

Thru 33mm dia splitter - peak air velocity is 0.449 Mach = 521ft/sec
Thru 35mm dia splitter - peak air velocity is lower, 0.400 Mach = 462ft/sec

Thankyou chris