I have a '66 425 block with a 455 crank and 7 inch rods and a piston pin height that matches a 455. This engine was free. It appears that it has 425 rods with 455 pistons and crank. Why would someone do this? Any ideas are welcome, I think from what I have been reading this would put the piston close to zero deck. If this is so, why are more people not doing this.? I can't understand why anyone would do this otherwise. I will attach pics of what I hope to install it in.

 

Simple math. The hard part is knowing which numbers to use.

The .125" difference in Pin (compression) height between the 425 (1.615") and 455 (1.740") was to compensate for the .250+" stroke and .265" Rod length increases.

Simple answer: At TDC, your pistons would be about .250" out of the hole.

Norm

 

The 455 pistons will be too tall with the 455 crank/7" rod combo.Here are your options:
455 crank,455 rods,455 pistons
455 crank,7" 425 rods,shorter piston(I have used a set of 455 Pontiac pistons for this combo,but there are others).
When installing a 455 crank into a 425 block,you will need to notch the bottoms of the cylinders,just as they did with the 455 blocks,to clear the additional stroke.
Using the longer rod reduces rod angle,& gives you a shorter,lighter piston at the end of the rotating assembly.
If you end up just wanting 455 rods,I have some,& I would be interested in your 425 rods,if you want to part with them.

 

Thanks for the answers. I will think about trading the rods with you. thanks for the quick responses. The car is a '42 Chevy, kind of nice to have an Olds in it.