If your tires aren't squealing in the turns, you're going too slow!(just sayin')
Unless the off ramp is downhill, you absolutely WILL NOT gain momentum on it. You would gain MORE momentum on a straight (downhill) off ramp, due to less tire scrub. And if you use your brakes, you've lost any advantage gained by the elevation gradient.
Gravity works to increase momentum. Centripetal acceleration has no effect on momentum, it only changes the direction of the momentum vector.