maxracesoftware wrote: ↑Mon May 14, 2018 2:01 pmHi John ... i thought the same thing when i read DrillDawg 's Post
... that was from an old Post of mine .
in PipeMax , i'm Looping thousands of times thru many different equations .. to calculate CFM at each crankshaft degreeCalculating CFM used from Dyno sheet ?
Post by swampbuggy » Fri May 11, 2018 10:54 pm
A formula was posted in the Debunker thread that stated you could calculate the CFM the engine used with this formula= H.P. divided by 8 divided by .26 gives you the CFM used + or - 10 CFM.
For torque peak CFM used----use this formula=peak tq. RPM x peak tq. divided by 9000 gives you CFM used at peak tq.
My question is directed at the following. The last engine i had was ma 516" BBC, the HP was 856 @ 6900 the TQ. was 693 @ 5900.
When i run the formulas as shown above i get the following.
CFM at peak HP should be 411
CFM at peak TQ. should be 454
The fact is the intake port flow signed off at 375 CFM at .800" lift.
So is this formula not always accurate or ???? Mark H
to arrive at Engine or Cylinder CFM Demand ... and this 1 line simple equation just about comes close to the same answer or result
... anyone could further fine-tune either Constants = 0.001030633 or 130 to suit their Data
CID = Cubic Inch displacement
Cylinders = the Number of Cylinders
VE% = the Volumetric Efficiency PerCent in a whole number , like 107.0 % VE
* = multiplication or like a similar sign x
an updated super simple empirical equation version is :
Intake Port CFM @28" = (CID * Peak HP RPM * 0.001030633 * VE) / (Cylinders * 130)
worked example :
Intake Port CFM @28" = (CID * Peak HP RPM * 0.001030633 * VE) / (Cylinders * 130)
Intake Port CFM @28" = (516 * 6900 * 0.001030633 *107) / (8* 130)
Intake Port CFM @28" = 377.53 CFM ..... Mark H 's CFM = 375 CFM @ 0.800" Valve Lift
107.0 VE input in PipeMax v3.98 makes 855.6 Peak HP ... Mark's Peak HP = 856.0 @ 6900
i could have nit-picked it closer to get exactly = 856.0 HP
more worked examples :
Briggs 6 HP Raptor 1 Cylinder
Intake Port CFM @28" = (12.568 * 4500* 0.001030633 *77) / (1* 130)
Intake Port CFM @28" = 34.52 CFM @ 28"
ProStock 500cid at 9800 RPM
Intake Port CFM @28" = (500 * 9800 * 0.001030633 * 125) / (8 * 130)
Intake Port CFM @28" = 606.98 CFM
Sonny's 1005.84 cid at 8000 RPM
Intake Port CFM @28" = (1005.84 * 8000 * 0.001030633 * 95) / (8 * 130)
Intake Port CFM @28" = 757.55 CFM
a 442cid SBC with Dart Pro 1's Ported to 245-246CC's 317 to 323 CFM making 816 HP at 8200 RPM
in another Thread on SpeedTalk :
Intake Port CFM @28" = (442 * 8200 * 0.001030633 * 90) / (8 * 130)
Intake Port CFM @28" = 323.26 CFM
Chris_Uratchko_466cid__CU_Marcella_SB_Chevy_ROX_1244_HP ( YellowBullet )
500 CFM Cyl Head Flow 9400 Peak HP RPM
Intake Port CFM @28" = (466.9 * 9400 * 0.001030633 *115) / (8 * 130)
Intake Port CFM @28" = 500.17 CFM
GreenLight's NHRA record setting Honda S2000 engine 7.96 ET in F/Dragster
360 CFM at 0.600 Lift on my Bench
Intake Port CFM @28" = (127.6 * 11000 * 0.001030633 * 128) / (4 * 130)
Intake Port CFM @28" = 356.09 CFM
128 VE supposedly on EnDyn's SF901 Dyno
Hoffman_32.6cid_7000RPM
32.60366191 Cubic Inches
Bore: 3.543" (90mm)
Stroke: 3.307" (84mm)
Rod Length: 5.709" (145mm)
Cylinders: 1
Compression: 10:1
Intake: 1.900" valve
Flow numbers at 28" with the entire intake tract bolted on (spigot,carburetor, velocity stack)
.100 61.6
.200 113.8
.300 172.5
.400 200
.500 208.3 <<----------
.600 216.3
Intake Port CFM @28" = (32.6* 7000 * 0.001030633 * 115) / (1 * 130)
Intake Port CFM @28" = 208.05 CFM
reduced ... even simpler easier equation version is :
Intake Port CFM @28" = (CID * Peak HP RPM * 0.000007928 * VE) / Cylinders
my SF-600 Bench is on the "conservative side" ,, around -15 CFM less ???
so someone applying my equation could adjust the CFM results to align with their Flowbench !
And how does any of that get you to camshaft size ?