Ok, if you want to do LOTS of damage in races, here's what you have to do: 1. If there is a Plasma Ray in the track, get it.
2. Once equipped, keep R1 pressed to charge it up until it is fully charged, but make sure you still have it charged until the following step.
3. Get an ammo refill, and the charged Plasma on the gun will become larger, increasing the damage.
4. Once the plasma gun is fully charged, with the ammo refill, get a double damage icon.
With all this, the damage will be devastating, lowering your foe to minimum health. The bad thing is that you must keep the gun charged throughout the whole race, waiting to collect the Ammo Refill and the Double Damage.