In this thread, we've got a few modifiers already for improved speed and maneuverability in the chart here
with modifiers for good to best handling and faster engines.
one has the earlier versions of the previous linked modifications.
But let's see if I can't add a few more for the generic listings..
Ok, so a supercharger is already in D20 Apocalypse, which grants +4 Init and +2 to Drive checks for the Dash stunt.
Turbochargers are fairly similar to superchargers, but isn't powered by the engine itself (less strain on the engine), and are more exhaust gas powered, and are somewhat more efficient, but usually have a more noticeable turbo lag (not always though) than superchargers..
Engine Modification, Turbocharger
This powerful addition to a vehicle's engine increases the vehicle's initiative modifier by +2 and provides a +4 bonus on Drive checks when attempting the dash stunt. PDC 13
Improved Fuel Economy
This is a modification to the engine, similar to adding a turbo or supercharger, but geared for improving fuel economy of the vehicle. The vehicle's range on a full tank of gas is increased by 25%. PDC 9
This kit adds a nitrous oxide injection system to the engine to provide more power and speed for short periods. However, with increased usage of the system requires greater maintenance of the engine. The NOS kit provides, when activated (standard action), the vehicle with a +1 Initiative bonus, increases speed by 4 squares and provides a +2 bonus on Drive checks to make a Dash stunt for 2 rounds. However, it also gives a -1 penalty to maneuverability for those two rounds, and increases Repair checks for the engine by 3. The NOS kit comes with a 5 use tank. PDC of NOS kit 16 Illegal (+4), each NOS tank has a PDC of 8.
Body kits are usually cosmetic alterations to the vehicle, but many have some improvements to the vehicle's performance, increasing aerodynamics, widening space between wheels or lowering center of gravity for better handling, etc.
Three versions of body kits are available: Speed enhancement, Handling enhancement, or Hybrid which combines features of both.
Speed enhancement body kits increase the aerodynamics of the vehicle's frame, reducing drag, increasing the vehicle's speed by 1 square. PDC 13 and requires 20 hours of work.
Handling enhancement body kits improve a vehicle's handling characteristics, by lowering center of gravity, widening the space between tires, lowering suspension, adding spoilers. The vehicle gains a +3 bonus to Maneuver. PDC 14 and requires 10 hours of work.
Hybrid body kits improve both the aerodynamics and handling of the vehicle, but not quite as well as a body kit for either. Speed is improved by 1 square and Maneuver is improved by +2. PDC 15 and requires 15 hours of work.
How about a few generic gimmicks..
Mounted onto the back of the vehicle are small, but powerful single use chemical rockets, designed to give the vehicle an incredible burst of speed for a short period of time, allowing for quick escapes. When activated, a standard action, the vehicle gains a +60 square boost in speed for 5 rounds, however the driver suffers a -5 to Drive checks. Rams made will gain 1 bonus die to damage if made within the first 2 rounds of the rockets' activation. Reduce cargo capacity by 50 lbs. Anything within 10 feet of the back of the vehicle when the rockets are activated suffers 2d6 fire damage.
PDC 15 (Illegal) To make the rockets concealed until use increase PDC by +2, replacement rockets have PDC 12.
The ever classic oil slick dispenser from every spy or action movie with tricked out cars. When activated, standard action, the vehicle releases oil behind it, creating an oil slick that is 15 feet wide and 30 feet long. Has a 5 use tank. PDC 16 Illegal (+4), uses 60 lbs of cargo space, refills cost PDC 5.