it's just like this...you increase the size of the cylinder, so more air gets sucked in to compensate for the larger size...that is, if you use the exact same pistons, just one larger to compensate for the increased bore...liikike for instance..my subaru is 10:1 and 2.5 liters, yet the pistons are dished....while 10:1 pistons in a 1.6 liter engine are waaay more than just dished