Head Flow Numbers

hytorksc

Registered User
Does anyone know where i can get a chart on how much total flow in cfm's it takes to make certain rwhp numbers? like this...

xxx cfm = 300 rwhp
xxx cfm = 350 rwhp
xxx cfm = 400 rwhp

i'm not sure i understand how all this works in terms of head flow ratings. if you take stock sc heads (a rough guess) at 190 exhaust/209 intake, is this the N/A flow rating for each cylinder? Do you add the flow of each cylinder to represent the total max flow of the heads?
i guess what i'm trying to figure out is what flow number at the heads will support various levels of rwhp, and how all this relates to boost levels. i know this is a very difficult concept to understand, at least in my mind. i don't even know if i'm asking this question in the correct way.

thanks-
 
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I think those would be NA numbers. Forced induction will increase flow acording to displacment of blower and boost numbers. Lets let the pro`s jump in here though.;)
 
AR's are awesome, they bring up the top end very nicely. i suppose this is all i should be looking for which would solve my search for power dilema. but money is the great barrier that stops this from happening, so i ask questions like this thread to see if i can find some loopholes or shortcuts somewhere :D

but i would like to have the question in this thread answered if anyone knows the answer.
 
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To be honest with ya, I'm not aware of a list like that. Besides, unless the comparison would be done on the same car with the same mods on the same dyno, same temp , etc it would be hard to document, even then you'd have your naysayers. I've seen many different Sc's hit 300 rwhp utilizing different set-ups, the point is it is always gonna be the sum of all the parts. The best flowing heads are only gonna gain you a little power with out the supporting mods.

Rick
 
I think the CFM numbers may change somewhat under boost, but remember that the increase in pressure is actually increasing the density of the incoming air. So maybe you're still drawing only 209 cfm under boost, but it's packed with a lot more molecules of air in that 209 cfm.
 
so i guess the bottom line what's important here is that i have to port the stock heads to flow well enough to support my hp target along with adding the right cam, and set up a supercharger that is well capable of outflowing them.
 
You'll need somebody with a flow bench to port them all equally.

My engine guy said the heads on my 94 looked pretty good and didnt need any work, so I didnt bother with the head porting sine I am on a relatively stock rebuild. You wouldnt calculate it according to your maximum horsepower desired .. that is achieved through your engine airflow + fuel intake plus the compression ratio, and engine displacement, etc etc ..


Anyways, heres an equation from an engine building book ..

You would calculate your air flow requirement based on displacement and maximum desired RPM and ensure that when the head is flow tested its flow rate exceeds the requirements of each cylinder.

(Ci Displacement / 1728 ) x RPM
-------------------------------
2

= CFM

CFM x 1.5 = Required head flow

CFM = Cubic Feet per Minute
In a stock build, CI should be about 232
The 1728 = 1 cubic foot ( 12x12x12) ..
And the 1.5 represents stock roller rockers ( I think we have 1.5 stock ? )

To calculate the CFM per cylinder you would use

([rpm x displacement] / 3456 )
---------------------------
Number of Cylinders

= CFM Per cylinder


In which case, 3456 represents 2 Valves, 2 cubic feet 1728x2

then Multiply the CFM per cylinder x Rocker arm ratio ( 1.5 stock )


Just an example of a little more information to go by. Both equations will give the same answer. Ive been toying with some of these numbers on a stock build and at 5000 RPM, im getting about 83 required CFM. ( Which is a good amount of air, thats over a Cubic foot per second, and overall Cfm is somewhere around 503 CFM, thats over 8 Cubic feet of air every second.) Where did you come up with the 190 and 209 Numbers ?? I believe those are Camshaft Degree dimensions. That has a little to do with the amount of air the heads will flow, it is a combination of the Camshaft Lift and Duration, Valve Size, and Rocker Ratio. Your heads flow as soon as the valve starts to open and increases to the maximum amount when the valve is fully opened.

- Dan
 
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thanks Dan for the good info-

Where did you come up with the 190 and 209 Numbers ?? I believe those are Camshaft Degree dimensions.

you may be right. i was just remembering off the top of my head, and probably got the numbers mixed up. what cfm does the stock heads flow at max?
 
thanks Dan for the good info-

Where did you come up with the 190 and 209 Numbers ?? I believe those are Camshaft Degree dimensions.

you may be right. i was just remembering off the top of my head, and probably got the numbers mixed up. what cfm does the stock heads flow at max?
 
thanks Dan for the good info-

Where did you come up with the 190 and 209 Numbers ?? I believe those are Camshaft Degree dimensions.

you may be right. i was just remembering off the top of my head, and probably got the numbers mixed up. what cfm does the stock heads flow at max?
 
thanks Dan for the good info-

Where did you come up with the 190 and 209 Numbers ?? I believe those are Camshaft Degree dimensions.

you may be right. i was just remembering off the top of my head, and probably got the numbers mixed up. what cfm does the stock heads flow at max?
 
S_Mazza said:
Check out this web page:

http://users.erols.com/srweiss/tablehdc.htm#Ford

Courtesy of Stan Weiss, it has flow data for all kinds of heads. He gives flow at a certain amount of lift and indicates the theoretical horsepower it can support. The SC stock heads are compared with Coy Miller and Steigemeier heads as well.
awesome- this is exactly what i was looking for. i realize this is theoretical, but it doesn't have to be exact, just ballpark. thanks again!!
 
Just keep in mind that some of those numbers at various amounts of Valve lift are obtained by the total amount of the height Camshaft is Lifting ( minus any play or flex in the pushrod ), multiplied by the roller rocker ratio .. will give you the amount of valve lift. The longer the valve is open, more air comes into the head .. it flows best at its total height. So in porting your heads, you may consider a different camshaft and a set of roller rockers with a different ratio .. or you just wont be maximizing the full potential of the head port. The chart doesnt list other modifications, just what numbers the head is flowing at the different valve heights .. unless they are all on a stock setup, but I highly doubt that.

- Dan
 
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Ddubb said:
Just keep in mind that some of those numbers at various amounts of Valve lift are obtained by the total amount of the height Camshaft is Lifting ( minus any play or flex in the pushrod ), multiplied by the roller rocker ratio .. will give you the amount of valve lift. The longer the valve is open, more air comes into the head .. it flows best at its total height. So in porting your heads, you may consider a different camshaft and a set of roller rockers with a different ratio .. or you just wont be maximizing the full potential of the head port. The chart doesnt list other modifications, just what numbers the head is flowing at the different valve heights .. unless they are all on a stock setup, but I highly doubt that.

- Dan
yeah, you can port the heads to the max, but it doesn't mean anything if the valves are not lifting high enough or long enough to take advantage- sort of like using a 90mm TB on a 65mm inlet plenum.. no real advantage. i do have another question- when head flow is stated in intake/exhaust numbers, does that number represent the total flow of that one head regardless of how many cylinders or is it by each port?
 
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