I am wanting to swap out my 390 in a 71 f100 and use a 351m from a 77 bronco. Will this bolt up to the my tranny or will i have to get the newer c6? Thanks

 

I hope you're not serious about this swap. The '71 390 had 255 horsepower, and the peak torque was at 2600 rpms and was 376 ft. lbs. of torque. The 351 M from 1977 had 148 horsepower with a torque rating of 243 ft. lbs. at 2400 rpm. You will be losing 107 horsepower and 133 ft. lbs. of torque...........Not a swap I would contemplate. Ford has a lot of easy swap options but they're not necessarily good options. You will have to get a C-6 Trans. which is for the 351m, 400, 429, 460 engines and then make sure you have the proper torque converter for the 351m. The torque converter is the only difference in these models of the C-6 trans. It has the "High" bellhousing. The 390 C-6 cannot be used with any of these four engines. Good Luck!

 

Keep the 390 its a much better engine . I have owned 351m and 400 , cant say I would replace a 390 with one , 460 ,yes , but the c6 is different like you have been told . I removed the 400 from my 79 bronco 15 years ago ,best swap I ever did . Much more power and it uses about the same amount of gas as the 400 .