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...you begin with the '1st-order' relationship:
Vg*Ag = Vp*Ap
where:
Vg = velocity of gas slug, fps
Vp = velocity of piston, fps
Ag = area of pipe the gas slug travels through, inches
Ap = area of piston, inches
where: area(A) = (pi/4)*dia^2; so: Ag = (pi/4)*d^2 and Ap = (pi/4)*B^2, where d = pipe diameter in inches and B = piston bore in inches, thus:
Vg / Vp = Ap / Ag = B^2 / d^2 (because the "pi/4" cancel)
...and, the 'mean' piston velocity is: Vp = RPM*S / 360, where S = piston stroke in inches.
...which yields: Vg = (RPM*S / 360)*(B^2 / d^2)
...finally, rearranging and solving for pipe diameter (d) you get:
d = SQRT[ RPM*S*B^2 / X ] ...where: X = 86,400(stock) to 108,00(race)
...if you're curious to know where "X" comes from, ask...
Last edited by gone-ot; 02-17-2010 at 09:04 PM..
Reason: added colors: red = pipe; blue = piston
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