my Low dollar 318 hop-up project

becase a closed chamber has a more compact chamber, better flame travel, with either a flat top or dished piston, less advance
tight quench with either gives detonation resistence and octane cushion
open chamber may have slightly more unsrouded valves, maybe not
they can make power runing in a stock class with good gas and where you always keep the rpm above the BMEP/ torque peak
for street NOT, you have to start making compomises that hurt the torque curve. efficiency/ mileage
That's why w put all the r&d into quench dome pistons- they flat work better
now with closed chamber heads you do not need them
The best thing to do with open chamber heads is to weld them up or cut them flat -if possible