Here you go, Piston area and force.
19.63/12.56= 1.563, equals an increase in area of 56.3%
IDK what your numbers are doing.......
except that 12.56/19.63 which is going the wrong way. We are looking at an increase, not the inverse.
The 36% increase from
@71340 is correct:
(19.63-12.56)/19.63 = 0.36
12.56/(1-.36) = 19.63
Let’s say that the tunes were matched somehow in the two different bores and everything else remained unchanged:
1,000 lbs/si * 19.63 si = 19,630 lbs force
1,000 lbs/si * 12.56 si = 12,560 lbs force
This is still a 36% increase in force on the piston:
(19,630-12,560)/19,630 = 0.36
The trick is to get the same, if not greater, explosion force out of the larger bore. This is somewhat easier to do when boring an engine for a rebuild, however the net change is far less…4.00 to 4.03 is only 1% increase (when rounding up).