underdrive crank pulley

[PBJ]

Hey guys,
Has anyone used a underdrive pulley on a viper? I have one on my corvette, but I had to slow the belt speed down, I was tossing belts over 7200 rpm. I never noticed much difference in performance, but I did notice the low rpm charging problems. I have installed numerous sets on mustangs and f-bodies with good results... most of those were 3 piece sets to speed the alt back up...so no charging issues. I just happened to see a ad on a crank pulley and I was just curious if anyone had installed one.
Thanks,
Joe

 

[Marv S]

Dave Schotz was selling them 4 years ago. I never heard of any problems. There were 2 different reduction ratios
http://vca1.viperclub.org/ubb/Forum2/HTML/000724.html

http://vca1.viperclub.org/ubb/Forum14/HTML/006464.html

 

[Greg D]

I installed a 25% underdrive crankshaft pulley on my 97 GTS. Can't say that I noticed a SOTP difference in performance, (and I didn't expect to) but I know that it had to help. My reasoning is that if it takes approx. 10 HP to turn the alternator, power steering pump, smog pump and water pump and you install a 25% smaller crank pulley, then it stands to reason that you reduced the the HP required to turn those mentioned accessories by 25% or 2.5 HP.

As for the charging system, Previously, My GTS usually charged at approx 14.2 volts. Now, with the 25% reduction pulley installed, Only at idle when I turn on the headlights, fog lights, air conditioning (full blast) rear glass defroster and put the car in reverse (to activate the back up lights) did the voltage drop to approx 13.3. As soon as the RPM's climb to a 1000 or more, the charging system returns to 14.2 volts.

I noticed no difference in the cooling systems effectiveness due to slowing down the water pump.

I have been told that slowing down the power steering pump
will reduce the chance of over heating the power steering fluid during extended track time.

Also see this past thread http://vca1.viperclub.org/ubb/Forum14/HTML/009208.html

 

[PBJ]

Thanks guys... I didn't think to go look at any prior posts.
Thanks again,
Joe

 

[Russ M]

I installed the 25% underdrive pulley and did before and after dyno pulls. There is a noticeable difference approximately 8-9 at the rear wheels.