I gave a friend a cam our engines are almost the same with the heads being the difference i could get 6200 to 6300 rpms from this cam. He can get only 5700 rpms we race on a asphalt 4/10ths oval track we know the valve springs are good will advancing or retarding the timing at full advance help us gain more rpms. we are using the same final drive 557 gear his heads are 58cc 305 heads with roller rockers my heads are 462 with stock rockers any help will be appricated