19cc domes are pretty high compression! Is there any porting.done to these pics?.If you dont know then post pics of cylinders. Dont go chasing displacement from your stock cylinders! Big bore stuff is 4 stroke business (to an extent). Why not sell the stock stroke hot rods crank and get a 4 mil. While youre at it, send those cylinders to Redline, Fast, or my fav Passion Racing! and get them ported and get some custom domes cut. 4 mil on stock ported cyl will run fine on stock carbs. Put some cpi's or whatever flavor you like and enjoy.