Quote:
Originally Posted by hat_man
That's why I ask here. 
Just out of curiosity....at what point would you have to change the length and would my theoretical idea come into play? |
Hi hat_man,
When I was rebuilding engines nobody would care until the compression ratio increased by more than 5%, and even then it was a big nothing. The biggest oversize I ever saw was .060. In the cases where the CR was imagined to get too high a thicker head gasket was used instead of short connecting rods - which would be custom made for too much money.
Assuming 3.78 inch diameter and 3.126 inch stoke, and that the combustion chamber is all in the head, so boring doesn't change the combustion space; .030 over size gives you 1.6% more displacement so 1.6% higher CR. 9:1 goes to 9.144:1 (or 9.4:1 goes to 9.55:1)
.060 would be 3.2% so 9.4:1 becomes 9.7:1
In general if the engine didn't ping before a .030 re-bore it wouldn't after either.
-mort