ive heard people say im not suppose to use an underdrive crank pulley with my flywheel. is this true ?

 

Lightweight flywheels reduce rotational mass.
Crank pulleys reduce parasitic loss.

Rotational mass is easy to understand, the lighter it is to spin, the faster the RPMS rise. Parasitic loss is any amount of power taken away from the engine to drive another motor or accessories. For example, when a motor has a Roots-style supercharger (comptech, jackson racing, etc), the motor must spin the supercharger to force the aircharge into the motor. While the aircharge does improve power, there is a significant amount of power lost because the engine has to use some of its output to spin the supercharger.

This is why when you turn the air conditioning on, your motor loses a small amount of power. The motor has to spin the A/C components with pulleys and belts to create the cold air for the cabin.

When you install aftermarket pulleys (crank pulleys), less engine power is given to the accessories and more to the crank. This simply 'frees up' efficiency (power) from the motor that would otherwise be sent to the alternator, for example.

There is no reason why you cannot run both, as the pulleys and flywheels work independently from each other.

 

I run a lightweight fidanza and lightened Crank, PS and water pump pullies. smile.gif love it

And Visionz explained it perfectly

 

That depends if you want to do things properly, or not. Most people don't, and most don't experience any ill-effect. Those that do experience ill-effect, generally lose the nose of the crankshaft. Because they didn't do things properly. And to do things properly, you will need to balance the pulley, the flywheel and the clutch together. Which entails having these parts out of the car. The costs associated are of course, quite high to do things properly. And so most people don't.



Your call m8, but for me I would just use the standard part for a road car.