If you are using a normal controller, you have to press the gas at an exact time and hold (like when the announcer says 2). It will hit the sweet spot if you press at exactly the right time. The timing is not what I said, but just practice by continually resetting until you find the exact timing...ALSO, venom and rapier probably have different timing.

Witha negcon you can hold the gas at that exact spot with an analog button, but its still kinda hard.