What kind of engine is it, and how many RPM's is it turning already?

To get faster, to an extent, you can turn off CapsLock, run higher nitro %, add a
properly tuned pipe, change the gearing in the car, or do some fancy machine work.
Obviously, if it's slobbering rich, you can lean it out a bit... though don't overdo it.
If it's already leaned out too much, and sagging on top end, try richening it up a bit.
You'll have to be more specific on what the symptoms are, before anyone can help much.