Steve, I know you know this, just thought I would post this for others.
The speed / a given velocity (FPS) through an orifice, is
determined by the size / area of that orifice, versus the
amount of air flow (CFM)that is flowing through that orifice.
While the information below is relative to flow / velocity
on a flow bench using a water drop of 28", the information
is relative, as flowing at a depression of 28" of water is
just about 50% of the velocity seen through a live engine.
So. . .If the velocity value at 28" of water depression is 200 fps,
then the velocity through a live engine would be 400 fps.
This engine is an NA 442 CID SB Chevrolet, which made 901 fwHP.
This amounts to 2.04 HP per CID,
and 1.41 Lbs Feet of Torque per CID.
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In past posts I have referenced the use of the 90%
rule regarding MCSA for the intake side.
As you can see below, this puts one right in
the 'Ball Park' regarding the intake valve. . . .
The correct area for the exhaust is highly dependent
on several variables, and is difficult to predict the
appropriate area for best Torque & HP, as related
to the appropriate velocity for a given exhaust port.
--- Cross-Sectional Areas at various Intake Port Velocities (@ 28 in.) ---
127 FPS at Intake Valve Curtain Area= 6.455 sq.in. at .934 Lift
216 FPS at Intake Valve OD Area and at Convergence Lift = .550
267 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 3.079 sq.in.
--- 8300 RPM Intake Cross-sectional areas in Square Inches ---
350 FPS CSA= 2.343 Port has Sonic-Choke with HP Loss ( too fast FPS )
330 FPS CSA= 2.487 Port may have Sonic-Choke with HP Loss ( too fast FPS )
311 FPS CSA= 2.639 Highest useable Port velocity ( possible HP loss )
300 FPS CSA= 2.736 Smallest Port CSA ( Hi Velocity FPS • good TQ and HP )
285 FPS CSA= 2.879 Smallest Port CSA ( very good TQ and HP combination )
260 FPS CSA= 3.156 Recommended average Intake Port CSA (very good TQ and HP)
250 FPS CSA= 3.283 Largest recommended average Intake Port CSA ( good HP )
240 FPS CSA= 3.419 Largest recommended average Intake Port CSA (less Peak TQ)
235 FPS CSA= 3.492 Largest recommended Intake Port Gasket Entry area CSA
225 FPS CSA= 3.647 Largest Intake Port Gasket Entry CSA ( Slow FPS )
215 FPS CSA= 3.817 Possible Torque Loss with Reversion ( Slow FPS )
210 FPS CSA= 3.908 Torque Loss + Reversion possibility ( too slow FPS )
200 FPS CSA= 4.103 Torque Loss + Reversion possibility ( too slow FPS )
Note : these are calculated average Port cross-sectional areas and FPS
--- Cross-Sectional Areas at various Exhaust Port Velocities (@ 28 in.) ---
127 FPS at Exhaust Valve Curtain Area= 4.252 sq.in. at .846 Lift
268 FPS at Exhaust Valve OD Area and at Convergence Lift = .400
331 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 1.629 sq.in. at 8300 RPM
--- 8300 RPM Exhaust Cross-sectional areas in Square Inches ---
435 FPS CSA= 1.239 Sonic Choke at Throat Area (too fast FPS velocity)
380 FPS CSA= 1.419 Sonic Choke at Throat Area (possibly too fast FPS)
350 FPS CSA= 1.539 Exhaust Port has Sonic-Choke with HP Loss (too fast)
330 FPS CSA= 1.634 Exhaust Port has Sonic-Choke with HP Loss (too fast)
311 FPS CSA= 1.734 smallest Exhaust Port ( very high velocity FPS )
300 FPS CSA= 1.797 smallest recommended Exhaust Port (Hi velocity)
285 FPS CSA= 1.892 smallest recommended Exhaust Port (Hi velocity)
265 FPS CSA= 2.035 Recommended average Exhaust Port CSA
250 FPS CSA= 2.157 Recommended average Exhaust Port gasket area
240 FPS CSA= 2.246 Recommended largest Exhaust Port gasket area
225 FPS CSA= 2.396 Largest Exhaust Port Exit gasket area (Slow FPS)
210 FPS CSA= 2.567 Largest Exhaust Port Exit gasket area (Slow FPS)
190 FPS CSA= 2.838 Torque Loss + Reversion + Scavenging loss (too slow FPS)
180 FPS CSA= 2.995 Torque Loss + Reversion + Scavenging loss (too slow FPS)
Note : these are calculated average Port cross-sectional areas and FPS
