CFM Calculation
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New User
Joined: Jun 2004
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CFM Calculation
Hey everybody,
Anyone know the max rpm for a 1966 f100 w/ 352?
I'm looking for a new carburetor and someone has suggested a holley 2300 (500cfm) but I wanted to know how they figured out the CFM for my truck. Holley's website recommends the following equation:
engine size (CID) x max RPM/3456 = cfm.
Any other thoughts or suggestions are always welcome.
Gary
Anyone know the max rpm for a 1966 f100 w/ 352?
I'm looking for a new carburetor and someone has suggested a holley 2300 (500cfm) but I wanted to know how they figured out the CFM for my truck. Holley's website recommends the following equation:
engine size (CID) x max RPM/3456 = cfm.
Any other thoughts or suggestions are always welcome.
Gary
Laughing Gas
Joined: Oct 2001
Posts: 957
Likes: 3
From: Winchendon MA
Well that calculation uses 100% volumetric efficiency witch most older engines can't due but its a start. Now you have to remember holley uses two different settings to rate there carbs!
They rate flow (CFM) with so many (xx) inches of vacuum on the manifold side during testing. 2 brl are rated with XX inches of vacuum and 4 brl rated with yy inches so the two don't compare this is how you can send a carb builder a 300 cfm carb and he'll send it back saying it flowed 600.
The 2300 will work fine on your truck.
44dwarf
They rate flow (CFM) with so many (xx) inches of vacuum on the manifold side during testing. 2 brl are rated with XX inches of vacuum and 4 brl rated with yy inches so the two don't compare this is how you can send a carb builder a 300 cfm carb and he'll send it back saying it flowed 600.
The 2300 will work fine on your truck.
44dwarf
Logistics Pro
Joined: Jun 2003
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44Dwarf is right, Holley's calculation is based on 100% volumetric efficiency. There is probably no engine made that is 100%.
Another more accurate formula that a lot of engine builders use is as follows:
CID X Max RPM X volume efficiency / 3456.
Volume efficiency for a full-race engine is probably 90%-95% (.90-.95).
A slightly modified street engine is around 80% efficient. (.80).
I would take into account the stock CFM of a mid 60s 390 and use that as a reference. I believe my 390 Mustang came with a 600 CFM carb.
Hope this helps.
Another more accurate formula that a lot of engine builders use is as follows:
CID X Max RPM X volume efficiency / 3456.
Volume efficiency for a full-race engine is probably 90%-95% (.90-.95).
A slightly modified street engine is around 80% efficient. (.80).
I would take into account the stock CFM of a mid 60s 390 and use that as a reference. I believe my 390 Mustang came with a 600 CFM carb.
Hope this helps.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
For a street engine cubic inches times 1.5 = MAXIMUM CFM.
Therefore a 352 x 1.5 = 528 so a 500 CFM carb is OK.
This is a much easier formula to remember than piddling around with guessing VE and max RPM's.
Therefore a 352 x 1.5 = 528 so a 500 CFM carb is OK.
This is a much easier formula to remember than piddling around with guessing VE and max RPM's.
Postmaster
Joined: Nov 2002
Posts: 3,447
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From: Littleton, CO
Originally Posted by 66_F100
Hey everybody,
Anyone know the max rpm for a 1966 f100 w/ 352?
I'm looking for a new carburetor and someone has suggested a holley 2300 (500cfm) but I wanted to know how they figured out the CFM for my truck. Holley's website recommends the following equation:
engine size (CID) x max RPM/3456 = cfm.
Any other thoughts or suggestions are always welcome.
Gary
Anyone know the max rpm for a 1966 f100 w/ 352?
I'm looking for a new carburetor and someone has suggested a holley 2300 (500cfm) but I wanted to know how they figured out the CFM for my truck. Holley's website recommends the following equation:
engine size (CID) x max RPM/3456 = cfm.
Any other thoughts or suggestions are always welcome.
Gary
--Mike
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
Why do you recon most guys think their FE needs 750s and the like?
What size is the 2 barrel that came on the truck, 350-390 cfm?
John
What size is the 2 barrel that came on the truck, 350-390 cfm?
John
Trending Topics
Logistics Pro
Joined: Jun 2003
Posts: 3,919
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Incidently, the NASCAR Craftsman Truck Series are only allowed to run 390 CFM carburetors when they run the 1 1/2 mile tracks.
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Senior User
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From: dundalk md
John,
Most of the 2bbls I seen on teh FE were 450 cfm. As for the 750 question, if ya gots the money to build a super high rpm motor, I think the cfms are needed to keep up for the high end. I do know the high rpms prefer a single plane manifold so it can suck gas down a cylinder from both sides of carb, so that is why I would guess high rpm needs the monster carb.
ron
Most of the 2bbls I seen on teh FE were 450 cfm. As for the 750 question, if ya gots the money to build a super high rpm motor, I think the cfms are needed to keep up for the high end. I do know the high rpms prefer a single plane manifold so it can suck gas down a cylinder from both sides of carb, so that is why I would guess high rpm needs the monster carb.
ron
New User
Joined: Mar 2004
Posts: 18
Likes: 0
From: Knoxville, TN
I have a had a 500 cfm holley two barrel on my truck for two years with no problems whatsoever. It is a 352 also. All I had to do was adjust the idle mixture screws and the float level.
Hope this helps
Hope this helps
Postmaster
Joined: Sep 2004
Posts: 3,166
Likes: 2
From: wi
if ya go to thedirtforum.com and click on menu go to the tool box and look under cfm requirments itll show you the most acuate cfm that ive found it shows for a 352 with max rpm @5000 you should need a carb with around 407.5 cfm @.80 volumeetric efficency hope that helps