i thought it's restricted to 200 no matter what you set it to
the speed limit is 200 torque units / 400 blocks per second, if you're confused
what i did was i set the mass of the vehicle to 100 to get above 149.9 torque units / 299.8 blocks per second, that's how i got above the 'speed limit'
the reason why most cars stop increasing their speeds at 99.9 torque units / 199.8 blocks per second is because their mass is set to 300, which limits the maximum speed allowed for the car