Calculating CFM used from Dyno sheet ?

[Scotthatch]

(Rpm\1000) x(displacement\2) = 100%ve.


(6900/1000) x (516/2) =


6.9 x 258 = 178


He should look at the numbers and see what makes sense.

693x5900/5252=778hp/8/.26=374, just what his head flows, 411/445(100%ve)=.92 or 92ve, his ve increased about 9% from torque peak to hp peak.


1780\4=445cfm

856hp\445 = 1.9hp\ cfm

445 x .26 = 115.7 - 445 = 329.3cfm


856\329 = 2.6hp\cfm


856\375 = 2.3hp\cfm

?? Not sure what you are saying?

I'm answering from my phone I messed up the post.

You misunderstand what I do ...the numbers are in relationship to steady state flow bench data and are not the same as what you are doing .... this confusion may be why people don't understand how to use the data to build a engine.... the basic idea is to start with cylinder head flow and build from that

[pastry_chef]

The CFM that an engine flows when making XXX power is one measurement.

The CFM that a head flows on a flowbench at 28 inch water is another measurement.

They have NOTHING in common apart from the letters CFM.

Disagree completely.
Some of the best in the industry have done this for decades.
But you can believe what you wish..

[DrillDawg]

For you to do your job you need to know what 100%ve is for the engine being built, You can do that with the first formula I posted and for his 516 at 6900 it's 1780 cfm total, you divide that by 4 (half the cyls.) and you get 445 per intake port, so now you know what your working for or what heads to pick to use. Anything above 100% VE can only be achieved with proper intake and exhaust sizing and cam timing no matter what the heads flow, you just need to know the how to take advantage of the extra flow if you have it and or cam it to peak at a higher rpm.

[user-23911]

The CFM that an engine flows when making XXX power is one measurement.

The CFM that a head flows on a flowbench at 28 inch water is another measurement.

They have NOTHING in common apart from the letters CFM.

Disagree completely.
Some of the best in the industry have done this for decades.
But you can believe what you wish..

For a start you need some sort of input for the number of cylinders.
Easy to assume it's 8 but often it's not 8 cylinders.

Then you need to know what sort of pressure you're dealing with.
High altitude is low pressure and forced induction is high pressure.

[pastry_chef]

For a start you need some sort of input for the number of cylinders.
Easy to assume it's 8 but often it's not 8 cylinders.

Then you need to know what sort of pressure you're dealing with.
High altitude is low pressure and forced induction is high pressure.

Yes, there are inputs other than raw CFM.

[Scotthatch]

For you to do your job you need to know what 100%ve is for the engine being built, You can do that with the first formula I posted and for his 516 at 6900 it's 1780 cfm total, you divide that by 4 (half the cyls.) and you get 445 per intake port, so now you know what your working for or what heads to pick to use. Anything above 100% VE can only be achieved with proper intake and exhaust sizing and cam timing no matter what the heads flow, you just need to know the how to take advantage of the extra flow if you have it and or cam it to peak at a higher rpm.

So with your way how do you figure out the cam you need and how do you know the rpm the engine will peak at ? Guess?

[pastry_chef]

(Rpm\1000) x(displacement\2) = 100%ve.


(6900/1000) x (516/2) =


6.9 x 258 = 1780


1780\4=445cfm

You begin with 516 cubic inches, then arrive at CFM required without converting (cu.inches to cubic.feet) ??

For a 516 engine @ 6900, I arrive at about 1030 CFM using 100% VE

[swampbuggy]

Guy's-----I love the discussion my thread has generated ! The main purpose for this thread (topic) was to try to get answers as to why the Engine produced the power it did with the head flow that it had 375 CFM. When everybody was saying that i would need 400 or more, i was excited when i returned home with that BBC in the back of my P.U. truck after the dyno session !!! Mark H.

[pastry_chef]

Guy's-----I love the discussion my thread has generated ! The main purpose for this thread (topic) was to try to get answers as to why the Engine produced the power it did with the head flow that it had 375 CFM. When everybody was saying that i would need 400 or more, i was excited when i returned home with that BBC in the back of my P.U. truck after the dyno session !!! Mark H.

I missed the compression ratio it had..

[DrillDawg]

For you to do your job you need to know what 100%ve is for the engine being built, You can do that with the first formula I posted and for his 516 at 6900 it's 1780 cfm total, you divide that by 4 (half the cyls.) and you get 445 per intake port, so now you know what your working for or what heads to pick to use. Anything above 100% VE can only be achieved with proper intake and exhaust sizing and cam timing no matter what the heads flow, you just need to know the how to take advantage of the extra flow if you have it and or cam it to peak at a higher rpm.

So with your way how do you figure out the cam you need and how do you know the rpm the engine will peak at ? Guess?

It's not my way, it's just information you have to have to know where your going, if you don't know how much it takes to fill a cyl. at whatever rpm how can you "guess" at anything else?


Pro stock 500 cuin., 11.0 x 250 = 2750/4 = 687.5cfm for 100% VE. You can't make a cam decision until you know if you can achieve those flow numbers or not, because I believe the closing point is the most important point.


If you can achieve those numbers you might be able to make 687 x 2.4 hp/cfm = 1650 hp.

[DrillDawg]

Guy's-----I love the discussion my thread has generated ! The main purpose for this thread (topic) was to try to get answers as to why the Engine produced the power it did with the head flow that it had 375 CFM. When everybody was saying that i would need 400 or more, i was excited when i returned home with that BBC in the back of my P.U. truck after the dyno session !!! Mark H.

You used all the 375cfm at the torque peak and the ram tuning effect let the engine use 411 at the HP peak, sweet results for sure.

[pastry_chef]

https://www.superflow.com/aspx/news.aspx?id=15

[swampbuggy]

PastryChef, to answer your question-----14 to 1 static C.R.------9.75 to 1 Dynamic C.R.--- Mark H.

[statsystems]

Guy's-----I love the discussion my thread has generated ! The main purpose for this thread (topic) was to try to get answers as to why the Engine produced the power it did with the head flow that it had 375 CFM. When everybody was saying that i would need 400 or more, i was excited when i returned home with that BBC in the back of my P.U. truck after the dyno session !!! Mark H.

Because the flow bench is NOT the do all, be all, end all for determining power. Many times I've lost flow on the bench and made more power and I'm not the only one saying that.

You need to learn to use the tool as a tool and not the end answer in a number.

[swampbuggy]

Thanks Pastrychef for posting the Superflow link, i found it very interesting ! Mark H.