In searching for replacement pistons for a rebuild of my 351C-4v engine, I’ve got a few questions. I’m replacing the block with an available 351C block. I’ve found some information suggesting that the '70 blocks are 0.020" shorter in deck height. The '71 and up are 9.206" deck height. The piston compression height along with the deck height and piston volume will determine the the compression ratio. One piston manufacture lists a piston compression height of 1.670" for the '71 and up blocks. These are flat top with valve reliefs of 2cc. This geometry with the taller deck height and the '70 4V heads (62cc) yields a 11.1:1 compression ratio. These pistons with the shorter '70 deck height could be problematic.
Does anyone know what the compression height is on the factory pistons (both '70 and later)?
Is the block deck height for the '71 and later correct as 9.206"?
Presumably the block vintage is correctly identified by the casting number D0AE-J and the later ones D1 something. This seems to be more of a machining issue than a casting issue but hopefully the casting number distinguishes them.
I’m looking to maintain the original compression ratio (perhaps a little lower but certainly no higher) and planning on rebuilding my existing '70 4V heads (62cc). I am currently looking for a replacement block don’t know what year that will be. Also I do not yet know what the final bore will be but want to be able to move forward with replacement pistons as soon as these parameters are known.
I don’t have a '70 shop manual. But the '67 and 1968 manuals list the deck heights of the pistons. So if you have the manual it will tell you. It’s a remarkably handy set of books to own. The CD / DVD / Digital download is OK but not as convenient as the paper IMHO…
I was of the understanding that the difference in CR for 70 to 71 was the heads having a slightly larger combustion chamber volume, but with what I find that may be, or not be. But 70 and 71 351C use the same casting number for the block with the 9.206 deck height. That deck height is listed as used for 1970 to 1974 351C, including the 2V the Boss, 4V, HO and CJ. I could not find this information in my 70 shop manual, I am getting this from Tom Monroe’s book, How to Rebuild your Ford V-8 351C-351M-400-429-460.
I may not be correct here. I am not an expert on this. But check again with the shop and ask if the have casting numbers for the blocks they used for there information.
However, 351W has 2 deferent deck heights. 1969 & 70 are 9.480 1971 up are 9.503. Again info from Tom Monroe’s book How to Rebuild your Small Block Ford.
If you know the crankshaft diameter you can install the crank and one rod and measure the compression height which is from the center of the small end of the rod to the deck - .030".
Or you could do like I just did -Google 351 Cleveland deck height. Within one second I had the answer.
Thanks everyone.
Badcat, that must be the only 351C book that I don’t have. I’m fixing that.
Another look through my library at George Reid’s Ford 351 Cleveland Engine does show the same 9.206 deck height for all.
The detailed description of the UEM KB pistons on the JEGS catalog is very specific “For 1971-up blocks. Pre-1971 blocks 0.020” shorter,…" These pistons have the most detailed description of any but are shown as having a 1.670" compression height. Most that I see advertised are in the 1.640" to 1.650" range. Many of the piston descriptions don’t say. https://www.jegs.com/i/United-Engine-Machine/648/KB177.030/10002/-1
I’ll need to further investigate the accuracy of the 1.670" height on the KB pistons before buying any of those, especially if the block needs much truing at the head surface. Need to maintain some piston deck height and don’t need to push the compression ratio any higher.
I clicked on the Jeg’s link that you provided. Under “Vehicle Fitment” it does indeed say that it fits 1971 - 72 351C. If You look at it more closely, it also says these pistons fit inline 6 cylinder, 302 cubic inch, and 429 cubic inch engines. Seems unlikely that would be true.
If I search for the .060" version of that piston it says it fits 1970 - 74 351 Cleveland engines - and nothing else. This is what I would describe as accurate.
My opinion would be to avoid buying mis - described parts. I would prefer forged pistons in any case. I would also prefer typical 1/16" / 1/16" / 3/16" ring sizes. That would double the purchase price but you get what you pay for.