needed cfm for 460
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Freshman User
Joined: Aug 2003
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From: WA State
needed cfm for 460
The '80 F250 460 AT 4x4 I bought has a Holley 1850-3 carb on it, 600 cfm I think & he also gave me a 625cfm Carter. What are your opinions on the needed cfm for the engine. What are the pro's & cons of each ?
.............Paul
.............Paul
Senior User
Joined: Jun 2003
Posts: 439
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From: Burnsville, MN
needed cfm for 460
Having a too large of a carb can cause all kinds of drivability issues. Problem is when you punch it, there will not be enough airflow through the venturis and the engine will stumble as you need some vacuum drop across the carb to work properly.
Only you can answer this question, very much like picking a camshaft - how will you drive the engine. If you are looking for torque then a smaller carb is better, raw horsepower at upper end of RPM a bigger carb is required. I used to have a flow formula for carb sizing but no longer - you should find something similiar on the 'net.
Only you can answer this question, very much like picking a camshaft - how will you drive the engine. If you are looking for torque then a smaller carb is better, raw horsepower at upper end of RPM a bigger carb is required. I used to have a flow formula for carb sizing but no longer - you should find something similiar on the 'net.
Senior User
Joined: Jun 2003
Posts: 439
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From: Burnsville, MN
needed cfm for 460
mud_man
Are you sure, it is late for me perhaps my math is in error...
300 cid @ 3000 RPM = 900000
900,000 / 3.145 = > 275000 (where do you get a 275 KCFM carb)?
perhaps it is cu/ft displacement = 1 cuft = 144 cu/in.
rough calculations again - cuz I'm tired.
300 cu / 144 = 2.2
2.2 * 3000 / 3.14 = 2000 CFM (still a bit big).
try this link -
http://www.speedfreaksspeedshop.com/en-us/dept_205.html
pr
http://realbig.com/pipermail/detomas...ch/008502.html
Are you sure, it is late for me perhaps my math is in error...
300 cid @ 3000 RPM = 900000
900,000 / 3.145 = > 275000 (where do you get a 275 KCFM carb)?
perhaps it is cu/ft displacement = 1 cuft = 144 cu/in.
rough calculations again - cuz I'm tired.
300 cu / 144 = 2.2
2.2 * 3000 / 3.14 = 2000 CFM (still a bit big).
try this link -
http://www.speedfreaksspeedshop.com/en-us/dept_205.html
pr
http://realbig.com/pipermail/detomas...ch/008502.html
Posting Guru
Joined: Sep 1999
Posts: 2,297
Likes: 1
From: Indiana
needed cfm for 460
enigma1
I have had good luck with a model 1411, Edelbrock, 750 CFM on mine.
I have ran both a Holley 4160, 600 CFM and this Edelbrock 750. For me, the Edelbrock seems to make more power especially at WOT. And it idles smooth as can be.
I have had good luck with a model 1411, Edelbrock, 750 CFM on mine.
I have ran both a Holley 4160, 600 CFM and this Edelbrock 750. For me, the Edelbrock seems to make more power especially at WOT. And it idles smooth as can be.
Postmaster
Joined: Mar 2001
Posts: 4,968
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From: So Cal
needed cfm for 460
Ballpark for general use would be maybe 750cfm. For best mileage get a good spread bore(Small primaries, big secondaries) and vacuum secondaries. For good mileage and responsiveness go smaller than the 750. For better high RPM or for a built engine go maybe with an 850.
I would probably not use an 850 on the street, but then I have no experience with this engine combo. I do know that my very strong 400ci engine turning over 6,000RPM was a bit boggy with an 850 Double Pumper with mechanical secondaries.
Most 460s are not high RPM engines so I would guess larger than an 850 would cause you to bog and get lousy mileage.
There is a formula in the Holly Carburator book, but I forget it exactly. In general an engine around 460 inches and turning less than 5,000RPM would be in the low 700cfm maximum, assuming very good efficiency etc.
A lot depends on the mods and how you plan to drive.
FWIW,
Jim Henderson
I would probably not use an 850 on the street, but then I have no experience with this engine combo. I do know that my very strong 400ci engine turning over 6,000RPM was a bit boggy with an 850 Double Pumper with mechanical secondaries.
Most 460s are not high RPM engines so I would guess larger than an 850 would cause you to bog and get lousy mileage.
There is a formula in the Holly Carburator book, but I forget it exactly. In general an engine around 460 inches and turning less than 5,000RPM would be in the low 700cfm maximum, assuming very good efficiency etc.
A lot depends on the mods and how you plan to drive.
FWIW,
Jim Henderson
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Elder User
Joined: May 2003
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needed cfm for 460
To calculate ballpark CFM use the formula: Displacement x redline (rpms) / the constant 3456. Note: This is NOT an exact formula, it does though, give the average person a good number to use when looking for a carb that will work.
Example: 429 ci x 5200 rpms / 3456 = 645.4861111 CFM.
As far as the original question of which carb, they are so close in CFM I don't think you would see much of a difference. The one that makes the truck run better and gives you more of what you want, power or fuel economy or both, is the one to use IMO. I've been using that exact same Holley 1850-3 600 CFM on my '71 429 and have found no reason to replace it (I never really rev over 3500 though, it's in an F350 DRW work truck). Here is a tip on it, if it does not have the power valve anti-blowout check valve in it I would recommend installing it. It's a small price to pay to keep you from having to deal with blown power valves. Good luck.
Example: 429 ci x 5200 rpms / 3456 = 645.4861111 CFM.
As far as the original question of which carb, they are so close in CFM I don't think you would see much of a difference. The one that makes the truck run better and gives you more of what you want, power or fuel economy or both, is the one to use IMO. I've been using that exact same Holley 1850-3 600 CFM on my '71 429 and have found no reason to replace it (I never really rev over 3500 though, it's in an F350 DRW work truck). Here is a tip on it, if it does not have the power valve anti-blowout check valve in it I would recommend installing it. It's a small price to pay to keep you from having to deal with blown power valves. Good luck.
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Posting Guru
Joined: Sep 1999
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From: Indiana
needed cfm for 460
Well, I will have to through this in here.
The Edelbrock 1411, 750 CFM produces the better mileage of the two ( Holley 4160, 600 CFM) "in my case".
Granted its not huge, but it is enough to notice.
And I have tuned both of them. Both carbs are new.
The Edelbrock 1411, 750 CFM produces the better mileage of the two ( Holley 4160, 600 CFM) "in my case".
Granted its not huge, but it is enough to notice.
And I have tuned both of them. Both carbs are new.
Post Fiend
Joined: Sep 2000
Posts: 8,238
Likes: 3
From: Oregon
needed cfm for 460
The minimum cfm for a 460 would be 750cfm. If its built up at all I'd recomend 850cfm and some say even a stock 460 can utilize 850cfm. Many of those with really hot 385s are running 1000cfm+. Its not a good thing to overcarburate, as is commonly done, but 460s seem to really gobble up the cfms.
Postmaster
Joined: Aug 2001
Posts: 2,882
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From: Nevada
needed cfm for 460
I'm with proeliator and Superdave. 460s like a lot of carburator. I've used Carter 625, Holley 750s, Edelbrock 750s, Predator variable venturi, Avenger 870 and Holly 850DP on various 460s and in every case on milder engines they preferred the 750 over the 625 (it was my 'back-up carb' for years). Same gas mileage but better throttle response and power with the 750.
Thread Starter
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Freshman User
Joined: Aug 2003
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From: WA State
needed cfm for 460
Thanks for all the input, Would I get the powervalve check if I bought a rebuild kit ? It needs it(re-building that is ). And is kick down linkage availible @like NAPA or is it a jy item ? Thanks
.................Paul
.................Paul
Elder User
Joined: May 2003
Posts: 549
Likes: 1
needed cfm for 460
Originally posted by enigma1
Thanks for all the input, Would I get the powervalve check if I bought a rebuild kit ? It needs it(re-building that is ). And is kick down linkage availible @like NAPA or is it a jy item ? Thanks
.................Paul
Thanks for all the input, Would I get the powervalve check if I bought a rebuild kit ? It needs it(re-building that is ). And is kick down linkage availible @like NAPA or is it a jy item ? Thanks
.................Paul