uncapped fps not uncapping

Anyone know the script for uncapping the fps in contra 006 because in the options its refuses to enable this feature?

i run an E6400 dual core 3 gig ddr2 800 gigabyte geforce 8800gt overclocked 1920 1980res and it always caps fps around 48 and then to 18-20 when things start to get hot on the battlefield. When the fps is around 30 it keeps on skipping frames and creates unnecessary lag even on my rig.