[dt]

I have a 3969854 block with a casting date of 12/22/1970. I have to assume this is a 1971 block ? Also would GM have used the same pistons from 1970 to 1971 on a 402?? Would they just change heads to effect compression #'s?

It seems the specs for the 71 402 show 300hp @ 8.50:1 C/R and the 70 402 to be 330hp @ 10.25:1 C/R.

 

[Twins Fan]

Lot's of things could have been changed over the past 40 years, so unless you're sure it's still completely stock who knows what's in there. Take a valve cover off and see what casting # the heads are.

To make the big compression change from '70 to '71 both the heads and pistons were changed.

 

[dt]

Yes I agree Brad. However, The engine appears to have stock flat top pistons as I have the heads off already. Thanks for your reply.