351m 2bbl
Fleet Mechanic
Joined: Feb 2001
Posts: 1,290
Likes: 15
From: Toronto, Canada
351m 2bbl
What is the cfm rating on my stock carburator?
I don't want to go to 4bbl and manifold for cost reasons, so would upgrading to a higher cfm give me more power without affecting mileage too terribly?
I hope the math is right, but I have gotten 16 mpg towing 2 horses 5 years before my rebuild.
Thanks,
Matt
1978 F250 Ranger 4x4 - 351M
I don't want to go to 4bbl and manifold for cost reasons, so would upgrading to a higher cfm give me more power without affecting mileage too terribly?
I hope the math is right, but I have gotten 16 mpg towing 2 horses 5 years before my rebuild.
Thanks,
Matt
1978 F250 Ranger 4x4 - 351M
Senior User
Joined: Feb 2001
Posts: 180
Likes: 0
From: Powell RIver Canada
351m 2bbl
I'm pretty sure that a larger cfm carburetor won't help that much at all. A friend of mine had a 750 double pumper on his mustang and went down to a 650 cfm carb and found he got more power. I guess he was getting too much fuel and it was choking his engine. Just remember bigger isn't always better. I have a 450 cfm carb on my 2bbl Cleveland so I'm guessing around the same on your M
Posting Guru
Joined: Aug 2000
Posts: 1,127
Likes: 3
From: (near) Denver USA
351m 2bbl
>What is the cfm rating on
>my stock carburator?
Matt,
The stock carburetor on your 1978 351M was the Motorcraft 2150. It was rated about 300-325 cfm.
>I don't want to go to
>4bbl and manifold for cost
>reasons, so would upgrading to
>a higher cfm give me
>more power without affecting mileage
>too terribly?
You can upgrade to the Motorcraft 2150 from a 1982 Mustang GT (carb #E2ZE), which is rated at 369 cfm. There is some power to be gained from that swap, particularly if you also add the 5/8" phenolic spacer used with the Mustang carb. It will really open up the 351M engine above 3K rpm, giving you more effective power up to 4.5K rpm or so.
I made this swap on my stock 1980 351M and my mileage is the same as before (10.5 city, 12.5 hwy), with a little better power.
Switching to a 400-500cfm 2V carb is probably overkill for your engine. I think you would suffer drivability problems, as the larger venturis and throttle bores will lower intake air velocity and give weaker control signals for the carb metering.
>I hope the math is right,
>but I have gotten 16
>mpg towing 2 horses 5
>years before my rebuild.
Driving style has a lot to do with mpg, but I've never seen anyone get that high mpg documented from a 351M, especially when towing or in any power-intensive application.
BubbaF250
1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.
>my stock carburator?
Matt,
The stock carburetor on your 1978 351M was the Motorcraft 2150. It was rated about 300-325 cfm.
>I don't want to go to
>4bbl and manifold for cost
>reasons, so would upgrading to
>a higher cfm give me
>more power without affecting mileage
>too terribly?
You can upgrade to the Motorcraft 2150 from a 1982 Mustang GT (carb #E2ZE), which is rated at 369 cfm. There is some power to be gained from that swap, particularly if you also add the 5/8" phenolic spacer used with the Mustang carb. It will really open up the 351M engine above 3K rpm, giving you more effective power up to 4.5K rpm or so.
I made this swap on my stock 1980 351M and my mileage is the same as before (10.5 city, 12.5 hwy), with a little better power.
Switching to a 400-500cfm 2V carb is probably overkill for your engine. I think you would suffer drivability problems, as the larger venturis and throttle bores will lower intake air velocity and give weaker control signals for the carb metering.
>I hope the math is right,
>but I have gotten 16
>mpg towing 2 horses 5
>years before my rebuild.
Driving style has a lot to do with mpg, but I've never seen anyone get that high mpg documented from a 351M, especially when towing or in any power-intensive application.
BubbaF250
1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.
