correct CFM
01-21-2002 | 08:16 PM
#1
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From: Connecticut
correct CFM
Building a 540 CI motor, 565 hp, merlin VR heads, Crane roller set up, Dart Manifold, Need to know what the best carb set up is.
Was recomended 800cfm, I think I should be running more.. HELP
Sheikman
Was recomended 800cfm, I think I should be running more.. HELP
Sheikman
01-22-2002 | 05:46 AM
#4
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From: Connecticut
Rumrunner
Compression ratio..9.5, cam is Crane#168731, 112 seperation, 288intake, 298 exaust, lift..587intake, 610 exaust, Hull is deepvee, Formula, 4200lbs, drive train, bravo 1, Merlin VR heads
Thanks for the help
Sheikman
Compression ratio..9.5, cam is Crane#168731, 112 seperation, 288intake, 298 exaust, lift..587intake, 610 exaust, Hull is deepvee, Formula, 4200lbs, drive train, bravo 1, Merlin VR heads
Thanks for the help
Sheikman
01-22-2002 | 09:04 AM
#5
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Joined: Jun 2001
Posts: 21,346
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Okay, here goes:
This is what I've been using for years and it works really well.
Basically the cubic feet per minute of air/fuel that your motor is displacing is a function of 1)the cubic inch displacement(CID) of your motor and 2)the maximum rpm range.
Since all four-strokes fill, burn and exhaust the mixture from each cylinder every 2nd revolution, you divide your CID by 2 to give you the volume of air displaced every rpm. Then multiply that by the max rpm range and you will get Cubic Inches per Minute displacement. Divide by 12^3(cubic inches per cubic foor) and you will get theoretical CFM. For high-performance engines with a good volumetric efficiency(Low resistance--ported, polished, good intake and exhaust) multiply by a factor of 0.90
If it is a stock motor, use 0.85 and for full-blown extremely efficient race motors use 0.95
For your application, here's an example:
CID=540
Max RPM=5500 (Just my guess)
VOL EFF=0.90
12^3=1728
(540/2) X 5500 X 0.90
--------------------- = CFM
1728
CFM=773
Something in the 800-850 CFM range should be okay. But be careful not to over carb.
This is what I've been using for years and it works really well.
Basically the cubic feet per minute of air/fuel that your motor is displacing is a function of 1)the cubic inch displacement(CID) of your motor and 2)the maximum rpm range.
Since all four-strokes fill, burn and exhaust the mixture from each cylinder every 2nd revolution, you divide your CID by 2 to give you the volume of air displaced every rpm. Then multiply that by the max rpm range and you will get Cubic Inches per Minute displacement. Divide by 12^3(cubic inches per cubic foor) and you will get theoretical CFM. For high-performance engines with a good volumetric efficiency(Low resistance--ported, polished, good intake and exhaust) multiply by a factor of 0.90
If it is a stock motor, use 0.85 and for full-blown extremely efficient race motors use 0.95
For your application, here's an example:
CID=540
Max RPM=5500 (Just my guess)
VOL EFF=0.90
12^3=1728
(540/2) X 5500 X 0.90
--------------------- = CFM
1728
CFM=773
Something in the 800-850 CFM range should be okay. But be careful not to over carb.
01-22-2002 | 09:28 AM
#6
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Posts: n/a
With that cam in a 540, It will be useless to spin the motor much past 5000 RPM, so the
800 CFM seems to be sized about right. There are some on this sight that really have had great luck with the Holley 830 [KAAMA comes to mind] in pretty similar applications. I'll be in the minority here, but I like your cam selection; should be a very mannerly engine with lots of torque.
800 CFM seems to be sized about right. There are some on this sight that really have had great luck with the Holley 830 [KAAMA comes to mind] in pretty similar applications. I'll be in the minority here, but I like your cam selection; should be a very mannerly engine with lots of torque.
