Hey all, I am wanting to know if the carb from the 302 will work on the 351M.

Here are the two trucks:

1978 F150, 302 2V, manual trans, non-emission, very simple looking engine.

1979 F150, 351M 2V, auto trans, was smothered with emissions at one time but it appears that everything has been "hacked" off the motor.



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A 302 will probably have a smaller venturi size and hence a lower CFM. Look on the side of the throttle body, there will be number stamped. It will be on the order of 1.08 or 1.21. Compare the two numbers. If the 302's number is lower, it may starve the motor.

Also, the 302 carb may be lacking the automatic kickdown linkage that your 351M carb has.

 

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Thanks for the info. I'll check the 302 carb for the linkage when I get out to where the truck is later today. If the trans linkage is not connected, do I risk harming the transmission?

The carb on the 351M is not the factory carb, so matching any numbers won't work.

Somewhat long story if you're interested/bored... I owned the '79 a couple years ago and traded it in at a local car lot. It had a new replacement carb on the motor. It also still had the factory 2.75 gears in the back. A year after trading it, I went up there and bought it back. I didn't take it for a test drive, but asked them if anything had changed on the truck since they got it. They said "No". Well some things did change - they swapped the new carb out for an old one that leaks gas all over the place and they swapped some 3.50 gears in place of the 2.73 gears. I'm not happy about them lying to me, and they offered to "undo" the deal since I was mislead, but I wanted the truck bad enough that I kept it anyway. So, that's how I know the carb on the engine doesn't belong on there, and it leaks gas real bad, so that's why I want to swap the good 302 carb on there for a while.

 

The kickdown linkage is what makes the transmission downshift when you get on the gas to pass someone on the highway, commonly referred to as a "passing gear." You don't harm anything by not having it hooked up, but you won't have as much power when you're trying to pass on the highway. This means your RPMs will be higher, so the input shaft on the transmission will be spinning faster which could put indirect stress on the transmission. But you can still manually downshift if you need to pass and can't do it with the pedal alone. Automatic kickdown is more of a convenience than anything else.

Here is some more useful information. A chart that I got from Offenhauser says that for a motor of around 350 cubic inches if displacement, and assuming you spend a lot of your driving in the 2500-3000 RPM range, then a carburetor around 300 CFM is acceptable. For example - my chart says the following

2000 RPM - 203 CFM
2500 RPM - 253 CFM
3000 RPM - 304 CFM
3500 RPM - 354 CFM

The 351M redlines around 5500 RPM, and my chart lists 557 CFM for that. My 400 cubic inch motor (50 more cubes) came with a 351 CFM stock carburetor, to give you an idea. That means it probably shifts around 3000 RPM, going by my chart. Based on the numbers above, you would need a carburetor around the 300 CFM range. Looking at the chart on FTE, that means a venturi size of 1.14 for a stock 2-barrel carb. So I'd be looking for carbs that say 1.14 on the side to put on your 351M. These are all just estimates, so take them with a grain of salt. You could always upgrade to a 4-barrel intake and carburetor