What exactly are the pistons dish cc’s on a 1970 high compression 350 vs the low compression 2bbl models ? I cc,d my existing 2 bbl pistons right around 20 cc’ s . I’ve read somewhere that number was 24 . I’ve also read in 73 they went to a lesser dish piston . If you plug in all the actual numbers my factory 350 2 bbl engine is more like 8.75 to 1 rather than the 9 to 1 advertised. Same goes for the higher compression 350 rated at 10.25 to 1 ( more like the high 9s). Thanks for any input.

 

That 20cc measurement sounds about right.

There were three different pistons used on the 68-70 350 engines:
10.5:1 compression flat top pistons used on the W-31
10.25:1 compression, 6cc dish pistons used on the 4bbl engines (non W-31)
9.0:1 compression, I don't have info on the dish (yours measured 20cc)

The 1971-1972 350 engines used the huge 23cc dish pistons and had (supposedly) 8.5:1 compression ratio. That correlates to your 9.0:1 pistons measuring 20cc (slightly smaller dish for slightly higher CR).

Then in 73-76 the combustion chamber volume was increased in the #8 heads and the piston dish was reduced to 14cc to keep the same 8.5:1 compression ratio.

 

Great information, thank you fun71 for supplying it. I just couldn’t seem to find it on the web .

 

According to the NHRA blueprint specs for the 1970 model year, the pistons in the low compression 350 were 18.13 cc dish, high compression were 5.10 cc. Of course the W31 pistons were flattops.

 

Thanks Joe that number is more aligned with my measurements and will help me figure out my compression ratio when all is said and done.

 

Keep in mind that NHRA numbers are the blueprint minimums. Factory pistons likely would have been a little larger due to manufacturing variability.