[mwebb]

Originally Posted by Old Tele man

...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*dia^2; so: Ag = pi*d^2 and Ap = pi*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's" 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...

i am asking
please o please but
while you are at it ...
two sets of variables ..... need to get resolved in one exhaust system -
at a wide range of rpm and load

this is looking like alchemy

..."...with Helmholtz tuning, the goal is to have the "reflected" rarefacation wave arrive back at the just closing exhaust value, so that it can literally "suck" the last vestiges of exhaust gas from the cylinder as the exhaust valve closes, which, if done correctly, will then actually create a slight vacuum within the cylinder that helps it "suck-in" more air when the intake value opens.

...the speed of sound in normal air is about 1,100 fps, but in hot exhaust it's about 1,700 fps (there's an approximation equation available if you're interested).
"...