[gone-ot]

For those who are interested, here are the abbreviated, simplified, Intake and Exhaust "tuning" equations:

LENGTH...acoustic tuning:

• L(int) = [IOICº × Vs(int)]/RPM = (Xº × 1100)/RPM ± 3"

• L(exh) = [EOIOº × Vs(exh)]/RPM = (120º × 1800)/RPM ± 1"

...where:

L(int) = Length, atmosphere to intake valve, inches.
L(exh) = Length, exhaust valve to collector, inches.
IOICº = Camshaft Intake Open-to-Intake Close (see Xº below), degrees.
EOIOº = Camshaft Exhaust Open-to-Intake Open (120º typical), degrees.
RPM = Engine speed where acoustic "tuned."
Vs(int) = Velocity of sound at 85ºF (intake air temperature) is 1100 feet-per-second.
Vs(exh) = Velocity of sound at 1000ºF (mean exhaust gas temperature) is 1800 feet-per-second (gasoline), varies with type of fuel.
Xº = Intake camshaft timing: 90º (max.race); 85º (race); 77º (high-perf); 72º (stock), degrees.

DIAMETER (inside pipe)...mass tuning:

• dia(int) = B×SQRT[(RPM × S)/(360 × Vg)], inches

• dia(exh) = B×SQRT[(RPM × S)/(360 × Vg)], inches

...where:

dia(int) = Intake runner diameter, inches; same cross-sectional area as intake manifold opening.
dia(exh) = Exhaust pipe inside-diameter, inches.
RPM = Engine speed where mass "tuned."
B = Piston BORE diameter, inches.
S = Crankshaft STROKE, inches.
Vg = Velocity of gas slug (intake or exhaust): 300 (race); 260 (hp); 245 (street); 240 (stock), feet-per-second. Limiting criteria, Mach index Z ≤ 0.6 (Vg ≤ 300 fps).