ORIGINAL: BMatthews
Adding a shim there would advance the port opening times and delay their closing times. Longer port openings may help the top end a bit.
Hmmmm -- an increase in deck height, with no other changes, will reduce compression and also shorten the duration of the power stroke. I'm not sure that will add to the top end -- but I haven't tried it, so .... anyone got some numbers? Larry Driskill or CombatPigg perhaps.