Last one, I don't agree with you and you don't seem like your gonna agree with us, lets just focus on the OP build, he's not stroking it anyways.
Combustion creates pressure, psi, my eg.. Was a 1000 psi (the psi of a average engine, full throttle) not a 1000 lbs of force, so the force from the piston would be F = P x A, larger piston more area for pressure to be applied = greater force to the rod.