A quick suggestion. If you want to model car physics the 8th chapter of Physics for Game Programmers (ISBN: 159059472X) is absolutely chok of helpful information for you. And nowadays it's pretty cheap too.

However, here are some helpful formulae for you:

There is a minimum Torque[Engine] value per car, and it does tend to have a maximu too. The minimum is all you should concern yourself over.

Code:
Torque[Engine] = Torque[Engine]*RPM;  // RPM is really the engine turnover rate, what we call revolutions per minute.

Ang_Vel = (2 * Pi * RPM) / 60; // This is the actual angular velocity in rad/s.

Power[Engine] = Torque[Engine] * Ang_Vel;

// Now we get into gears and the transmission...

Torque[Wheels] = Torque[Engine] * Gear_Ratio[Current] * Gear_Ratio[Max];
That's about all I can give with my understanding. I'm sorry that I can't help you much more, but that's some of the basics for you.