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What is the main difference performance wise between the two engines? Also, still looking on how to identify the two. I was told to decode the VIN but did not have much success there. VIN is X15HKDJ5248. Have there ever been 1979 Supercabs with a factory installed Cleveland?
The 351 C was discontinued in 1974.The way that I tell the difference is the bolt pattern on the bell housing is wider on the 351 M.It has the same pattern as the 400 and the 385 series engines (370,429,and 460) engines.If the engine is still the original,it will be the 351M or a 400.In the late 70's Ford had a difficult time keeping up with the high demand of the 351 Windsor engines and placed a 351 W crank in the 400 engine and created the 351(modified) engine.It was essentially a 400 engine destroked with a 351 crank.Most people make the common mistake and refer to the 400 as a modified engine.It is not.The 351 M was the only modified.There should be a decal on the drivers side valve cover with either the 351M or 400 on it.
The correct designator for the 351C is a 335 engine,not a small block.
Another way to tell a modified from a Cleveland is to measure the deck height. The blocks are very similiar but a totally different size all the way around. There are almost no interchangeable parts from one engine to the other. I know because I did this very swap in 1982. The engine also will sit lower in the engine compartment, so I had to modify the engine mount supports so the headers I was using would work. The earlier poster is correct you will need a different transmission. I traded my 385 series c-6 with the large pattern bellhousing for a 335 series. The bellhousing does not come off like on a c-4 so the tranny will have to change.
I did this swap when I was in high school, so alot of it was halfa** due to a lack of funds. But the motor ran great once I got it all set up right.
Thanks Sel for the time warp update. Original thread started 5-17-07, updated by you on 11-27-08. It is a nice read anyway, like to read info from guys that have the knowledge. Wonder what happened to SVT tech? His input was also more than just BS. Talk more later.
the 351m also had issues with spark knock due to running unleaded gas. The 351C didn't have those issues.
I made my 351m/(400.... to a 406) run like a scaled dog.... but still had to run mid grade anytime lug was going to be put on the motor. Had TONS of power though, and would run away from most trucks even with 3:50 gears and 37in tires, and a stock C6.
The 351 C engines were used in Australia for a number of years after they were discontinued in the U.S. As far as I know they were not used in any trucks at all and discontinued in passenger cars in 1974.