351 question

whichever 351 is based on the 400 block be it the windsor or cleveland I was having a discussion how do they make a 400 into a 351? Destroking or what? I can't figure it out how they make a 400 into a smaller 351. Can anyone explain? Thanks

I thought the 400 was based off the 351M. Cause, for intance, back in the late 70's there was a 351M/400 option for the F-series trucks. I do believe the difference is the stroke too, but I could be wrong.

Speaking of 400, woohoo 400 posts. Yeehaa! :icon16:

I thought the 400 was based off the 351M. Cause, for intance, back in the late 70's there was a 351M/400 option for the F-series trucks. I do believe the difference is the stroke too, but I could be wrong.

Speaking of 400, woohoo 400 posts. Yeehaa! :icon16:

Yep, the 351M, almost a boat anchor.

The 400 came first and was designed for trucks and large passenger cars. It is based of the Cleveland block with some differences like main journal size and it's bellhousing pattern for big-blovk transmissions. Then due to the gas crunch and clean air acts Ford de-stroked the 400 to 351cu hence the name 351M M=modified.

These motors are great for what the intended purposes esp. trucks. But as far as for Mustangs and performance applications boat anchors would be the correct term. LoL

The 351M was designed to replace the 351C. Ford only used the “M” designation to distinguish it from the 351 W (Windsor) and the 351C (Cleveland). The “M” designation has now become know to mean “modified” or “Michigan,” even though the 351M was produced at both the Cleveland foundry and Michigan casting center, and originally had no meaning but as an identifying mark.

The 351M is pretty close in comparison to the 351C. The stroke is still 3.5, but the main journal diameter enlarged from 2.75 inches to 3.0 inches to allow for a greater bearing wear area. The 351M is also close in comparison to the 400 (destroked 400=351M), and all have one big thing in common. The valve trains are all interchangeable (except pushrods) and the cylinder heads are all compatible. The 351M is designed to make more low end torque for bigger cars and trucks, and was built with emissions regulations in mind that the 351C couldn't handle. Lastly the 351M was mass produced from 1974 till 1979, but still popped up in some Broncos, F250 and F350's till 1982.

HiFlow you sound like an encylopedia. :bigthumb:

so by "de-stroking" do ya mean that they put a smaller crank and longer rods or just a smaller crank?

Rod length has nothing to do with stroke, because if a longer rod travels (for instance) .5" higher to TDC, then I will be .5" higher than BDC as well. It is the crank that increases stroke that is correct. So a 351M is a 400 with a shorter crank stroke.

I'm not completely sure of it, but I believe the 351 had a 3.50 stroke, while the 400 had a 4 inch stroke, both had 4 inch bores. Here's something that might help. http://www.fordcobraengines.com/Modified%20History.htm