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Old 02-16-2010, 05:36 PM   #67 (permalink)
gone-ot
...beats walking...
 
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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 08:04 PM.. Reason: added colors: red = pipe; blue = piston
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