force to run 60Hz for vga?

[sega88]

hi everyone,

Im new to this board and would like to ask if anyone know or success to enable vga support with these following dc games.

(all selfboot)

Hydro thunder (Kalisto)
plasma sword
MTV skateboarding
The ring US
Sky of arcadia US
King of fighter 99
soul fighter
(the last blade)--> havent try yet

I bet all these games run in 50hz or so, and this may be one of the reason that i m not success to enable the vga support for them.

if anyone good in hexediting im pretty appreciate if u can tell me how to change the 50Hz and force them run in 60Hz!!