Just did some quick calcs, guessing at a few things but to give an idea:
250cid+30-over
58cc head
.040 gasket
.000 deck
flattop piston (0cc dish)
11.59CR
The 70cc head would give
9.97CR
(Gain of 1.6 CR with the small head - at this level!)
Back to the small head, 58cc
11.59CR
Mill head .020
Guess that the gain is about 2/3 of that by milling the block, since milling the quench area takes away no volume
12.03CR
So if you started with the above, my guess is you'd have to mill the head .020" to get 12.03CR.
Now, my small head is 59.4cc bone stock as I last measured it, and chamber work will normally make it bigger. So, you might end up having to mill .040" or so to really get 12.0cr.
Even on my stock spare 250 -
Compression with my stock large head
72.5cc measured
8.15CR (a real snoozer)
With my stock small head
59.4cc measured
9.29CR
Gain of 1.14 CR.
So the small head gains 1.1 to 1.6 CR on things we would typically build. Does it also gain torq/power? That I suppose is the topic of this very enthusiastic (even fun?) thread. Hey, at least people care!
