I just bought a 1975 f-100 4X4 and was told it had a 390 motor. Problem is the VIN has a Y on the 4th digit which means it originally had a 360. The other problem with identification is that it also has a 4barrell carb which did not come on the 360s from what I have been told. The 390s did have that option. The blocks on the 360s and 390s all say 352. I could find out the stroke length with a rod but probably would not be to sure of myself and the results there. If I drop the oil pan, what would the number be on the crankshaft to identify the size of the motor for a 390 or a 360? I would GREATLY appreciate any help I can get, as no person Ive talked to seems to know.

 

You will have to measure the stroke. I don't have the numbers, but I am certain they have been posted many times before, so do a search to find them. The only difference between the 360 and 390 is the crank stroke and the pistons, the bore is the same, the rods are the same.

 

360 is 3.50 inches, 390 is 3.78 I believe. Take a plug out and measure, its what I did, you'll know whatcha got then.

 

Thanks guys.

But I am having to drop the oil pan for a gasket leak anyway so I was just thinking that would be a easy way to see the size of the motor as well if it is on the crankshaft. I just dont know the number that would be on the crank to identify a 390 or 360. Are you saying the only way to truly know is measure the stroke and that I cant get it off the crankshaft?

 

2T or 2TA stamped on the crank would ID it as a 3.50 stroke (360).

2U, 2UA or 3U stamped on the crank would ID it as a 3.78 stroke (390).

 

Thank you guys very much. This will help a great deal. I love this site.

 

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