Underdrive Crank pulley

What are you feelings on underdrive crank pulley's?

They are not a bad idea for a high output motor. One thing to remember everything will spin slower. Watch your alternator voltage if you run them. It may cause a low voltage output that your electronics may not like. Don't forget to run an electric radiator fan. The fan is the biggest source for parasitic drag.

Thanks Tcmaboy,
The good thing is I already have two 12" electric radiator fans, replacing the stock fan. I heard without the harmonic balancer, I am endangering my engine. Is that true?

Getting a pully set that dosen't include a balancer in the crank pully is not a good idea. Your main bearings and crank will wear rather quickly. I know high preformance balancers exist. I don't know if they include an underdrive. If the crank pully eliminates the harmonic balancer I would have the engine balanced to compensate.