If this is a car to be used for actual racing I presume the pumps will all be at full speed during a race?
When you are not racing, perhaps it would be simpler just to switch off some of the pumps when less fuel flow is required. That would only require the Arduino to control relays. Solid State Relays would be easiest if your budget can stretch to them.
If you do need to control the motor speed you will need to find a suitable high-amperage motor control board that can interface between the motors and the Arduino.
...R