Okay just something im wondering. What is the difference between a 351 w piston and 302, pin height? skirt lenght? im wondering because if its the skirt lenght why couldnt you cut the skirt down to use them to make a 393. Just a thought. i know i have seen engine builders by dome pistons and cut the domes off to get more compression the flat tops will even provide. Anyone have info on this?

 

Hello, 351W pistons have a 1.77-ish compression height(center of pin to top of piston) from the factory, and a 302 piston is a 1.6-ish compression height from the factory. this compression height number can change a little depending on who manufacturs the piston, and what compression ratio they want to achieve... and by change I mean =/-.010" or so... you could set up the piston below deck, above deck, shave the block a bit, shave the heads, etc. also head gasket thickness can have a significant affect on compression, but you need a good .040" piston to head clearance on a street or highly loaded engine.

thanks, Jeff.

 

Ok to figure out what compression height you need or how to stroke an engine you need to do some measuring. You need the deck height (center of crank to the top of the block) which would be 9.503 on a later block and 9.480 on the earlier blocks, that’s how much room we have to work with. So a 393 has a stroke of 3.850 and we need to divide that in half (1/2 the stroke) which would be 1.925 now add the rod length 5.956 = 7.881 So 9.503 (deck) Minus 7.881 (1/2 the stroke and the rod) = 1.622…..that would be the compression or pin height you would need to put the top of the piston right at the top of the block.

½ stroke 1.925
Rod 5.956
Piston 1.622

That would work in a 9,503 block but would put the piston out of the block .023 with an early block. So look for a piston that gets the job done and that would be a 302 piston….1.608 height on most of them but there are some that are different so make sure you get the one you want. A 302 with a CH of 1.608 would put the piston down the hole .014 which is ok on a 9.503 block but on a 9.48 block they would stick out .009 and even that would be ok with good rods……

And in your case you have an early block .009 out the hole would be a good thing, it would make a perfect quench for high compression engine less detenation and a cooler chamber. I ran a 302 with them .010 out and it loved it no problems at all. You would need dished pistons with the 393..........

Ok I’m all done hope that helped if not Oh well!

 

thank you that helped allot