What would it take to make 1.44 lbs-ft per cid ?
Not saying these formulas work but to me they seem like there in the ballpark.
Trying on the original reasonably efficient Trick Flow 408 example from post #1.
https://www.motortrend.com/how-to/408-inch-budget-mopar-westech/
514 hp @ 5,900 rpm 1.26 hp per cid.
526 tq @ 4,000 rpm 1.29 lbs-ft per cid.
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According to these formulas a 408 that peaks at 6000 rpm, needs a minimum push rod pinch csa of 2.23" sq and 299 cfm heads with an average csa of 2.52" sq and port volume of 204 cc for a 285 fps.
Trick Flow say the flow 300 cfm with a port volume of 190, not sure of pinch csa probably a little shy of 2.23" sq. The calculated csa average is 2.34" sq which gives a calculated 308 fps which according to the chart is the "highest usable port velocity with very good hp and tq but with possible hp loss"
This is at 100% ve more ve and or rpm is gonna run these heads at a higher velocity and obviously less ve and or rpm a lower velocity etc..
As for minimum csa it seems to be design to happen at peak hp.
300 cfm x 2.4 / 2.23" min csa = velocity at peak hp 323 fps @ 6000 rpm.
To me It seems like average csa is supposed to happen around peak torque, there's a formulas for intake and header average csa to tune for 260 fps at peak torque (cid / cylinders) x peak torque rpm / 88200 = average csa.
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These formulas are based on 100% ve and we'll use 100% in this example.
VE% x cid = usable cid = 408.
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First is to figure out need head flow, cfm = usable cid x rpm x .0009785 / 8
Cfm 299 = 408 x 6000 rpm x .0009785 / 8
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Next minimum csa which is usually push rod pinch.
Min csa = cid x rpm / 1,100,000
Min 2.23" sq = 408 x 6000 rpm / 1,100,000
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Next average csa and port cc for desired fps (velocity) which we'll say is 285 fps.
Based on 4.95" port length and port flow of 299 cfm and port average csa.
Port volume cc = port length x 16.387 x csa.
Fps = cfm x 2.4 / csa.
300 fps = 2.39 csa = 195 cc
285 fps = 2.52 csa = 204 cc
260 fps = 2.76 csa = 224 cc
If you look at these calculated recommended fps with very good hp and tq you got a range of 260-300 fps with 285 fps being in the halfway between the two, and seems like 240-320 fps is considered the maximum usable range. Which is a port size of 243 cc to 182 cc for 299 cfm head.
I'm sure there's circumstances to use out side of 240-320 fps.
Trick Flow 408
Not saying these formulas work but to me they seem like there in the ballpark.
Trying on the original reasonably efficient Trick Flow 408 example from post #1.
https://www.motortrend.com/how-to/408-inch-budget-mopar-westech/
514 hp @ 5,900 rpm 1.26 hp per cid.
526 tq @ 4,000 rpm 1.29 lbs-ft per cid.
------------------------------------------------
According to these formulas a 408 that peaks at 6000 rpm, needs a minimum push rod pinch csa of 2.23" sq and 299 cfm heads with an average csa of 2.52" sq and port volume of 204 cc for a 285 fps.
Trick Flow say the flow 300 cfm with a port volume of 190, not sure of pinch csa probably a little shy of 2.23" sq. The calculated csa average is 2.34" sq which gives a calculated 308 fps which according to the chart is the "highest usable port velocity with very good hp and tq but with possible hp loss"
This is at 100% ve more ve and or rpm is gonna run these heads at a higher velocity and obviously less ve and or rpm a lower velocity etc..
As for minimum csa it seems to be design to happen at peak hp.
300 cfm x 2.4 / 2.23" min csa = velocity at peak hp 323 fps @ 6000 rpm.
To me It seems like average csa is supposed to happen around peak torque, there's a formulas for intake and header average csa to tune for 260 fps at peak torque (cid / cylinders) x peak torque rpm / 88200 = average csa.
-----------------------------------
These formulas are based on 100% ve and we'll use 100% in this example.
VE% x cid = usable cid = 408.
--------------------------------------
First is to figure out need head flow, cfm = usable cid x rpm x .0009785 / 8
Cfm 299 = 408 x 6000 rpm x .0009785 / 8
-------------------------------------
Next minimum csa which is usually push rod pinch.
Min csa = cid x rpm / 1,100,000
Min 2.23" sq = 408 x 6000 rpm / 1,100,000
-------------------------------------
Next average csa and port cc for desired fps (velocity) which we'll say is 285 fps.
Based on 4.95" port length and port flow of 299 cfm and port average csa.
Port volume cc = port length x 16.387 x csa.
Fps = cfm x 2.4 / csa.
300 fps = 2.39 csa = 195 cc
285 fps = 2.52 csa = 204 cc
260 fps = 2.76 csa = 224 cc
If you look at these calculated recommended fps with very good hp and tq you got a range of 260-300 fps with 285 fps being in the halfway between the two, and seems like 240-320 fps is considered the maximum usable range. Which is a port size of 243 cc to 182 cc for 299 cfm head.
I'm sure there's circumstances to use out side of 240-320 fps.
Trick Flow 408