Quote:
Originally Posted by mwebb
ok, so why then the magic 300fps
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...that's the 'critical' gas velocity where gas-slug "friction" with the pipe walls becomes excessive. For race engines (full-race hemi) that's about 300 fps, but for street engines (non-hemi, wedge, and pent-heads) the value is typically 80% of this, or ~240 fps.
...camshaft valve timing and engine RPM affect header
length (valve to end-of-pipe/atmosphere):
L(intake) ~ 85*Vs/RPM, where: Vs ~ 1050-
1100 fps in air.
L(exhaust) ~ 120*Vs/RPM, where: Vs ~ 1600-
1800 fps in hot exhaust.
...here,
85 and
120 are
typical values representing, respectively, a percentage of the intake- and exhaust valve durations, in camshaft degrees. If you know the actual values for your engine, use them instead. Header lengths (L) are in inches.