Calculating CFM used from Dyno sheet ?
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Re: Calculating CFM used from Dyno sheet ?
Hi Scott,
I noticed those graphs in Harold Bettes' Engine Airflow book, thought they were very interesting.
Can you provide an example please.
I noticed those graphs in Harold Bettes' Engine Airflow book, thought they were very interesting.
Can you provide an example please.
Mike R
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Re: Calculating CFM used from Dyno sheet ?
"That motor was taken out of my 72 Chevy shortbed P.U. and went straight into a TOP quality Horton rail type dragsterswampbuggy wrote: ↑Mon May 14, 2018 7:29 pm THANKS-THANKS-THANKS Larry M. You are the very best at writing information that (I) for 1 and probably (NOT) the only one can REALLY grasp . If my old sweetheart was @ 107 % V.E. that tickles the S*** out of me. That motor was taken out of my 72 Chevy shortbed P.U. and went straight into a TOP quality Horton rail type dragster and went 8.20-8.30's out of the gate. Oh BTW the P.U. was a street toy, and no it was not tubbed, it was a BLAST with a Richmond 5-Speed and 3.73 posi.
and went 8.20-8.30's out of the gate. "
i almost didn't see your Post .
i hope the equation is useful for future Projects
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Re: Calculating CFM used from Dyno sheet ?
OK ... kinda did at the beginning of the thread
The engine that started this is 856 HP
The cam is 282 installed on a 107
1/2 of 282 is 141 plus 107 = 247
247 - 180 puts intake closing point at 67 degrees
Since we need at l/d=.1 not .050 we will cheat and just pull 20 degrees of the top so 47 degrees
If you look at the chart at 47 you go up to the cross line and back toward n that's 1.12
So 375 cfm x 1.12 = 420 cfm
420 x .257 x 8 = 863.5 HP
The engine that started this is 856 HP
The cam is 282 installed on a 107
1/2 of 282 is 141 plus 107 = 247
247 - 180 puts intake closing point at 67 degrees
Since we need at l/d=.1 not .050 we will cheat and just pull 20 degrees of the top so 47 degrees
If you look at the chart at 47 you go up to the cross line and back toward n that's 1.12
So 375 cfm x 1.12 = 420 cfm
420 x .257 x 8 = 863.5 HP
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Re: Calculating CFM used from Dyno sheet ?
I pulled this one from clay Smith cams
Cam is a roller 233@.050 550 lift
Heads are Afr 210 so at 550 lift flow 301 cfm
Intake closing point is 40 degrees
Down and dirty pull 20 off to get to l/d=.1
Off the chart 20 degrees comes out to .9
301 cfm x .9 is 270.9
270.9 x .257 x 8= 557 HP
It made 544 but they said there was 10 more in it
Cam is a roller 233@.050 550 lift
Heads are Afr 210 so at 550 lift flow 301 cfm
Intake closing point is 40 degrees
Down and dirty pull 20 off to get to l/d=.1
Off the chart 20 degrees comes out to .9
301 cfm x .9 is 270.9
270.9 x .257 x 8= 557 HP
It made 544 but they said there was 10 more in it
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Re: Calculating CFM used from Dyno sheet ?
http://tbichips.com/?page_id=112
Engine uses edelbrock etec 200 heads
So flow @ .400 is 223
Flow@ .500 is 252
Cam lift is .444 so call flow @ lift 229
Comp 12-402-4 cam 212@.050 flat tappet 114 lc
Closing point at .050 is 40 degrees
Down and dirty for flat tappet is -25 degrees so l/d=.1 is 15 degrees which charts to .88
229 cfm x .88 = 201.5
201.5 x .257 x 8 = 414 HP
Engine uses edelbrock etec 200 heads
So flow @ .400 is 223
Flow@ .500 is 252
Cam lift is .444 so call flow @ lift 229
Comp 12-402-4 cam 212@.050 flat tappet 114 lc
Closing point at .050 is 40 degrees
Down and dirty for flat tappet is -25 degrees so l/d=.1 is 15 degrees which charts to .88
229 cfm x .88 = 201.5
201.5 x .257 x 8 = 414 HP
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Re: Calculating CFM used from Dyno sheet ?
If you are building something and you want more accurate then my down and dirty then you need to figure l/d=.1 better and what that stands for is lift/diameter of the intake valve when it = .1 that just means when valve lift is 10% of the valve dia so with a 2.02 valve it's at .202 lift and with a 2.19 valve it's .219 lift ... to find this point you would need to take rocker ratio and figure tappet lift then look at the cam profile to figure duration at that tappet lift then figure the closing point ... most of the time I find I don't have enough information on the profile to do that ..... next option is if you have the cam you can find this point as you degree it in ... that gives you better numbers to check against the dyno run to see if you got it all running correctly ...
The other thing to note is that you need cfm of the whole system and intakes are not tested as much as they should be .... if head / cam calculated HP is way high as to the dyno tested horsepower and intake is not a known value then you can be pretty sure it's a problem
With what I have covered so far you can see how tested flow and cam size works ... also you can see why ramp speed and rocker ratio and valve size will effect that HP number and why sometimes cam Co will add a few degrees to the closing point to make that cam make just a bit more power ...
Once you guys have a good handle on this part we can go over that formula and how I use it and what it tells us
The other thing to note is that you need cfm of the whole system and intakes are not tested as much as they should be .... if head / cam calculated HP is way high as to the dyno tested horsepower and intake is not a known value then you can be pretty sure it's a problem
With what I have covered so far you can see how tested flow and cam size works ... also you can see why ramp speed and rocker ratio and valve size will effect that HP number and why sometimes cam Co will add a few degrees to the closing point to make that cam make just a bit more power ...
Once you guys have a good handle on this part we can go over that formula and how I use it and what it tells us
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Re: Calculating CFM used from Dyno sheet ?
Scott,
If you get a Comp Cams Master Lobe List it will show tappet lift @ TDC which help give you a better idea about a cam (for your .1 l/d) with actually having the cam.
Also some flow software will additionally show what the l/d is on the report.
Stan
If you get a Comp Cams Master Lobe List it will show tappet lift @ TDC which help give you a better idea about a cam (for your .1 l/d) with actually having the cam.
Also some flow software will additionally show what the l/d is on the report.
Stan
Code: Select all
In. Valve 2.55
0.25D In. 637.5
CFM
Actual Observed L / D
Valve Flow Ratio
Lift InchIntake Intake
0 0 0
200 148 0.078
300 241 0.118
400 335 0.157
500 421 0.196
600 492 0.235
700 546 0.275
800 567 0.314
900 578 0.353
1000 583 0.392
Stan Weiss/World Wide Enterprises
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http://www.magneticlynx.com/carfor/carfor.htm
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Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
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Re: Calculating CFM used from Dyno sheet ?
I have the lobe lists that I can get ... most of the time you kinda have to guess from the listed data as they where not ment to show this point on the lobe profiles that is why i crunched as many as I could and came up with the cheat adjustment .... the cams I use I plot out so I know for next time which means I tend to use the same onesStan Weiss wrote: ↑Tue May 15, 2018 10:27 am Scott,
If you get a Comp Cams Master Lobe List it will show tappet lift @ TDC which help give you a better idea about a cam (for your .1 l/d) with actually having the cam.
Also some flow software will additionally show what the l/d is on the report.
Stan
Code: Select all
In. Valve 2.55 0.25D In. 637.5 CFM Actual Observed L / D Valve Flow Ratio Lift InchIntake Intake 0 0 0 200 148 0.078 300 241 0.118 400 335 0.157 500 421 0.196 600 492 0.235 700 546 0.275 800 567 0.314 900 578 0.353 1000 583 0.392
Most other people I have used this to help are OK if it is off by even 10 HP they want the big number not the fine tuning
Re: Calculating CFM used from Dyno sheet ?
This formula was also in my old note book but I don't think I ever really used it.
rpm x (cuin per cyl) \ 2000(10" test presure) x 1 .67 (28" conversion)
6900 x 64.5\2000 x 1.67 = 371 cfm
Right at what he said his heads flowed.
375\411= 91% or 411\375=1.096% which way you want to look at it, VE\cfm increased around 9% from torque peak to hp peak.
rpm x (cuin per cyl) \ 2000(10" test presure) x 1 .67 (28" conversion)
6900 x 64.5\2000 x 1.67 = 371 cfm
Right at what he said his heads flowed.
375\411= 91% or 411\375=1.096% which way you want to look at it, VE\cfm increased around 9% from torque peak to hp peak.
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Re: Calculating CFM used from Dyno sheet ?
Maybe I misunderstood, but how does VE increase from peak tq to peak hp?DrillDawg wrote: ↑Tue May 15, 2018 1:08 pm This formula was also in my old note book but I don't think I ever really used it.
rpm x (cuin per cyl) \ 2000(10" test presure) x 1 .67 (28" conversion)
6900 x 64.5\2000 x 1.67 = 371 cfm
Right at what he said his heads flowed.
375\411= 91% or 411\375=1.096% which way you want to look at it, VE increased around 9% from torque peak to hp peak.
Re: Calculating CFM used from Dyno sheet ?
I figured his hp at torque peak and with the formula I used before suggested he was using all the 375 cfm that his port flowed and as he reported the "dyno" suggested he was using 411cfm at hp peak, about 9% difference, I had added cfm while you where posting.
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Re: Calculating CFM used from Dyno sheet ?
True, that mass flow through an engine increases with rpm (to a point) but VE doesn't past max work/peak torque.DrillDawg wrote: ↑Tue May 15, 2018 1:37 pm I figured his hp at torque peak and with the formula I used before suggested he was using all the 375 cfm that his port flowed and as he reported the "dyno" suggested he was using 411cfm at hp peak, about 9% difference, I had added cfm while you where posting.
Re: Calculating CFM used from Dyno sheet ?
The one thing I see with trying to use CFM alone is that if the heads, intake, carb and cam are not sized correctly the tq will not be there.
I have a dyno sheet of a 357 that made 530 hp but only 400 ft lbs. with a little over 300 CFM.
I have a dyno sheet of a 357 that made 530 hp but only 400 ft lbs. with a little over 300 CFM.
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Re: Calculating CFM used from Dyno sheet ?
I struggled with that too ... when I first figured this out I realized that I had a HP number but no rpm .... the interesting thing at this point is that you can get a number this way so that means something else sets the rpm but not the HP .... when it came to torque I new the relationship with HP but not the why ?
The one thing I should point out is that we are only setting one cam event .. intake valve closing..... there are 5 more events and I have been playing with those ... from what I have seen the intake opening event and exposure of the intake valve at peak piston velocity has a lot to do with torque .... from what I have seen so far you need 5.75 cfm per cubic inch of the cylinder at peak piston velocity to have any hope of filling the cylinder and you have to balance that with not to much overlap depending what peak rpm will be ... the higher the rpm the more overlap you can deal with ... yet another reason to keep low lift flow up
The one thing I should point out is that we are only setting one cam event .. intake valve closing..... there are 5 more events and I have been playing with those ... from what I have seen the intake opening event and exposure of the intake valve at peak piston velocity has a lot to do with torque .... from what I have seen so far you need 5.75 cfm per cubic inch of the cylinder at peak piston velocity to have any hope of filling the cylinder and you have to balance that with not to much overlap depending what peak rpm will be ... the higher the rpm the more overlap you can deal with ... yet another reason to keep low lift flow up
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Re: Calculating CFM used from Dyno sheet ?
Scott ,.... the following Info is what i calculate using v4.00 :
Basic Engine + Head CFM Data :
for 486.6 Peak TQ ... its possible you could have made 424.8 Peak instead of 414.4 HP
...v4.00 shows it could have used higher Valve Lifts to get 424.8 Peak HP
CSA + FPS + Port Volume CC Data :
Basic Engine + Head CFM Data :
Code: Select all
Peak TQ = 486.6 at 3800 RPM BSFC=0.390 Fuel=130.1 333.5897436 UBHP= 1.055488086 HPCF 13.737:1 A/F
Peak HP = 414.4 at 5200 RPM BSFC=0.447 Fuel=174.8 391.0514541 UBHP= 1.059707094 HPCF 13.910:1 A/F
AirDensity%=94.2 at 5200 RPM
Performer RPM E-Tec 200 Cylinder Heads For S/B Chevy
Cylinder Head Specifications:
Combustion chamber volume: 64cc
Intake runner volume: 200cc
Exhaust runner volume: 80cc
Intake valve diameter: 2.02"
Exhaust valve diameter: 1.60"
Valve stem diameter: 11/32"
Valve guides: Maganese bronze
Deck thickness: 5/8"
Valve spring diameter: 1.46"
Valve spring maximum lift: .575"
Rocker stud: 3/8"
Guideplate: Hardened steel
Pushrod diameter: 5/16"
Valve angle: 23°
Exhaust port location: Stock
Spark plug fitment: 14mm x .750 reach, gasket seat
Code: Select all
#60989 | #60985:
Flow Numbers as tested by Edelbrock's SuperFlo SF-1020 flow bench @ 28" H2O
Valve Lift .100" .200" .300" .400" .500" .600" .700"
Intake 67 122 175 223 252 259 265
Exhaust 57 110 153 182 196 204 207
Intake CFM @ 0.444 Lift = 239.1281
Exhaust CFM @ 0.444 Lift = 189.6405
Code: Select all
Part Number: 12-402-4 Grind Number: 260AH-14
Lifter Type: Hydraulic Flat Tappet
Engine Family: Chevrolet 262-400 c.i. 8 cyl. 1958-1998
Description: Good for stock TPI 350 or TPI 305 with modified computer.
Cam Family: Computer Controlled
Specifications Intake Exhaust
RPM Range: 1500 to 5500 Valve Lash: Hyd Hyd
Valve Timing: 0.006 Duration: 260.0 268.0
Lobe Separation: 114.0 Duration@.050" Lift: 212.0 218.0
Intake Centerline: 110.0 Valve Lift: 0.444 0.444
Lobe Lift: 0.296 0.296
Valve Timing @ 0.006 Lift: 20/60=Intake 72/16=Exhaust 110.0 CenterLine
...v4.00 shows it could have used higher Valve Lifts to get 424.8 Peak HP
CSA + FPS + Port Volume CC Data :
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