[Rez]

The way it works is that the relay switches on and off really really fast. If it spends more time off than on, the car goes slow. If it spends more time on than off, it goes faster. This is how the proportional throttle works, it adjusts how long the switch is on and how long the switch is off, right up till it's always on at full throttle.

As Neurokenetic said, provided the relays can keep up, you'll keep your proportional throttle, even with the mod.

So what's the word, Bigshot? Can the relays handle the frequency?

To better answer your question, the relay switches one circuit on when current is applied to another. That means the 5v from the electronics can be used to close 14v to the motor, thus the sensitive electronics can control a dangerous level of voltage. The proportional speed of your car isn't controled by variable voltage, but by variable frequency. If Bigshot's relays can operate at a high enough frequency, this mod should be entirely transparent to the driver.