Replacing carb - Right size CFM?
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From: Cary NC USA
Replacing carb - Right size CFM?
I have a '69 F-100 with 360.
After difficulty with remanufactured Motorcraft carb I am thinking about buying a new one. Edelbrock sounds like a dependable choice but Holley's are readily available.
?? Size in cfm - the stock 2bbl 2100-123 is rated at 356 cfm. The Holley comes in 500cfm and I was told 600cfm but parts store said not in 2bbl.
Someone told me that each step bigger carb would burn more fuel. That doesn't make sense to me because the engine should only need a certain amount of fuel/air mix regardless of what the carb is able to deliver.
?Should I just look for a replacement 350 cfm or go bigger??
Thanks,
Richard
After difficulty with remanufactured Motorcraft carb I am thinking about buying a new one. Edelbrock sounds like a dependable choice but Holley's are readily available.
?? Size in cfm - the stock 2bbl 2100-123 is rated at 356 cfm. The Holley comes in 500cfm and I was told 600cfm but parts store said not in 2bbl.
Someone told me that each step bigger carb would burn more fuel. That doesn't make sense to me because the engine should only need a certain amount of fuel/air mix regardless of what the carb is able to deliver.
?Should I just look for a replacement 350 cfm or go bigger??
Thanks,
Richard
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From: Laveen
Replacing carb - Right size CFM?
You can over carb. an engine, if the venturi/s are to large the air velocity through the venturi will be insufficient and the fuel won't atomize properly and yes this could cause fuel economy problems, I have a Carter 650 I think on a 351 but when you calculate how many RPM,s you can turn at 351CI and 650CFM it comes out to something like 8000 RPM's, not going to happen on a stock 351M so even a 500CFM would have been good, but I got a really great deal on the 650
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Replacing carb - Right size CFM?
Sorry to burst your bubble, but there is no such thing as a 650 CFM Carter AFB carb.
As for CFM requirements, it depends on the engine and its use.
Stock engines are very inefficient. With some running below 70% volumetric effifiency. Those engines do not need much carb.
When an engine is built using flowed heads, tuned intakes and matching cams efficiency raises with some naturally aspirated engines (NASCAR) reacing 110%. Turbos and Superchargers enhance or fool the engine into making it more efficient than it is, hence bigger carbs, but...
Just look at Nascar. They run 9 grand all day do not use much bigger carbs than 800 CFM. Daytona and Talladega they use even smaller to curb the restrictors.
600 CFM 4 barrel carbs are excellent for stock engines, plus I would almost garauntee you will see an INCREASE in gas mileage over a 2 barrel.
Josh
As for CFM requirements, it depends on the engine and its use.
Stock engines are very inefficient. With some running below 70% volumetric effifiency. Those engines do not need much carb.
When an engine is built using flowed heads, tuned intakes and matching cams efficiency raises with some naturally aspirated engines (NASCAR) reacing 110%. Turbos and Superchargers enhance or fool the engine into making it more efficient than it is, hence bigger carbs, but...
Just look at Nascar. They run 9 grand all day do not use much bigger carbs than 800 CFM. Daytona and Talladega they use even smaller to curb the restrictors.
600 CFM 4 barrel carbs are excellent for stock engines, plus I would almost garauntee you will see an INCREASE in gas mileage over a 2 barrel.
Josh
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From: Cary NC USA
Replacing carb - Right size CFM?
Thanks Josh and other contributors,
I sent the question to Holley tech services, will be interested to her their response.
Big question? Since my '69 truck w/ 360 FE does not have be emission tested should I go for one of the carbs listed as off-road not emission compliant or should I buy the street legal variety. It is only intended for general driving but with a 16 year old in the driving pool who knows.
If we later went for the expense of a rebuild another carb could be added.
Richard
I sent the question to Holley tech services, will be interested to her their response.
Big question? Since my '69 truck w/ 360 FE does not have be emission tested should I go for one of the carbs listed as off-road not emission compliant or should I buy the street legal variety. It is only intended for general driving but with a 16 year old in the driving pool who knows.
If we later went for the expense of a rebuild another carb could be added.
Richard
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Replacing carb - Right size CFM?
When examining specs of those "emissions" it just seems like a good ploy to make a couple extra bucks on the same carb you can get for much less.
Standard 600-650 CFM Holleys are what you are looking for, although I have heard some great things said about those new Holley Avenger Carbs.
If you really want to get involved you can also examine whether you want center hung or side hung floats, dual inlets or one, chrome or natural and it goes on and on...
With that you can kinda see why some of us have several carbs sitting around. It's an addiction.
Josh
Standard 600-650 CFM Holleys are what you are looking for, although I have heard some great things said about those new Holley Avenger Carbs.
If you really want to get involved you can also examine whether you want center hung or side hung floats, dual inlets or one, chrome or natural and it goes on and on...
With that you can kinda see why some of us have several carbs sitting around. It's an addiction.
Josh
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From: Cary NC USA
Replacing carb - Right size CFM?
Thanks,
Holley said that a 350cfm would work on the stock 360CI-FE for normal street driving, and best fuel economy, and that a 500cfm would be a slight performance upgrade without modifications to the engine.
This is based upon the idea of low volumetric efficiency for a stock engine.
Do you carburetor junkies coat your gaskets with pam kitchen spray, recommended somewhere, to reduce gasket scraping when switching?
Scraping that carb to manifold gasket(at least wo were in there) was not much fun.
Richard
Holley said that a 350cfm would work on the stock 360CI-FE for normal street driving, and best fuel economy, and that a 500cfm would be a slight performance upgrade without modifications to the engine.
This is based upon the idea of low volumetric efficiency for a stock engine.
Do you carburetor junkies coat your gaskets with pam kitchen spray, recommended somewhere, to reduce gasket scraping when switching?
Scraping that carb to manifold gasket(at least wo were in there) was not much fun.
Richard
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Replacing carb - Right size CFM?
Is this a 350 CFM 2 Barrel?
I cannot understand why Holley is recommending the 350 CFm carb. I wouldn't put a 350 on my lawnmower.
But it is your engine.
Holley does have a replacement carb for the 70's Ford Truck. Rated at 600 CFM it is part # 80453.
And it only costs $7.00 more than that 350 CFM 2 barrel.
But I still recommend either a universal 600 CFM Holley carb or an AFB style carb.
I have never had problems with sticking carb gaskets.
Do not forget you aren't using all 4 barrels to just drive around. The 4 barrels only kick in when you really get on the gas.
Josh
I cannot understand why Holley is recommending the 350 CFm carb. I wouldn't put a 350 on my lawnmower.
But it is your engine.
Holley does have a replacement carb for the 70's Ford Truck. Rated at 600 CFM it is part # 80453.
And it only costs $7.00 more than that 350 CFM 2 barrel.
But I still recommend either a universal 600 CFM Holley carb or an AFB style carb.
I have never had problems with sticking carb gaskets.
Do not forget you aren't using all 4 barrels to just drive around. The 4 barrels only kick in when you really get on the gas.
Josh
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From: Cary NC USA
Replacing carb - Right size CFM?
Thanks Josh,
350 for a lawnmower, huh!
I may check around the junk yards here in NC for a 4bbl manifold before I order anything.
Can't stand the $250 plus for a new manifold.
I did read that the 4bbls are fuel effficient if you keep your foot out of the carb.
Richard
350 for a lawnmower, huh!
I may check around the junk yards here in NC for a 4bbl manifold before I order anything.
Can't stand the $250 plus for a new manifold.
I did read that the 4bbls are fuel effficient if you keep your foot out of the carb.
Richard
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Replacing carb - Right size CFM?
I guess I overlooked the fact you are dealing with a complete 2 barrel system.
D'Oh!
Anyhow, stock 4 barrel manifolds (although very heavy) are somewhat common in the boneyards.
I know a 4 barrel set-up would be much more to your liking than a 2 barrel.
Josh
D'Oh!
Anyhow, stock 4 barrel manifolds (although very heavy) are somewhat common in the boneyards.
I know a 4 barrel set-up would be much more to your liking than a 2 barrel.
Josh
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From: Fairborn USA
Replacing carb - Right size CFM?
I currently run a Holley 750cfm with the black heavy spring in the secondary. But I have run a Holley 350cfm with no probs.
You can look at the pics on my web page of my engine. Its not stock anymore and will run just fine on a 350cfm. Just doesn't have the OMPH I like. It did get better mileage tho.
1969 F250 with a 1967 Cougar 390cid 315HP+
Tim
You can look at the pics on my web page of my engine. Its not stock anymore and will run just fine on a 350cfm. Just doesn't have the OMPH I like. It did get better mileage tho.
1969 F250 with a 1967 Cougar 390cid 315HP+
Tim
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From: texarkana, tx
Replacing carb - Right size CFM?
kc8fhs ---
Thanks for the web site link ---- I like your pix! I see your hood has insulation on the bottom AND you are running headers in one of the pix....doesn't that make for a very hot engine compartment?
Did you make the web site yourself?....if you did, can you drop me a line at my email here on the forum?
Thanks....
Thanks for the web site link ---- I like your pix! I see your hood has insulation on the bottom AND you are running headers in one of the pix....doesn't that make for a very hot engine compartment?
Did you make the web site yourself?....if you did, can you drop me a line at my email here on the forum?
Thanks....
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From: Urbandale, Iowa
Replacing carb - Right size CFM?
I also have a 390 two barrel. I have seen not only intakes, but heads referred to as 2V or 4V. Would switching from a 2 barrel to a 4 barrel require a head change as well as an intake change.
THanks
THanks
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From: Concord, NC
Replacing carb - Right size CFM?
Aren't there two versions of the Holley 2300 two barrel? I think there's a 350 and a 500 cfm version. A friend of mine races, and he says that you can actually get the 350 cfm to outflow the 500 cfm. This being said, this is at wide open throttle running in circles around a race track at 6200rpm. So, I'd say go with a small 4 barrel so you can open it up if you ever wanted to. I'm pretty sure Offenhauser makes a 4 barrel intake manifold for the 300-6, but I know cost was an issue for you, so that might not be feasable. But if you don't want to go through finding an intake manifold, the one of the 2300's should work ok.
