Greetings. I just installed a underdrive crank and alternator pulley. I anticipated that I would have a reduced charging issue. With my lights on and blower motor on full my voltage (on the guage) drops to the hash above 8 volts at idle and as soon as I hit about 800 rpm it spikes right back up to normal. Prior to this install I was sort of questioning my alternators performance anyways as it seemed like it wasn't charging like it used to. So I'm wondering if a new alt would be beneficial. I'm going to test the alt when I get to work (parts store) to see how it's really doing. Hopefully someone else can chime in that has underdrives installed so I can compare.

 

Have not done the under drive pulleys. But that it is expected to drop it down some. But all the way to 8 volts does not sound good. Ya it may need to be replaced. Have you tried a voltmeter to see exactly where it at? If you have to you can upgrade to a higher amperage output but at Idle it probably will not change.

 

Ok so I tested the setup at work and its at 11.7 volts at idle with EVERYTHING on (bright lights, blower motor on high, wipers on high, stereo cranked, electric fan on). Yeah 11.7 sounds bad but thats only at idle, at 1000 rpm I have 13.2 volts. I am going to swap back to the stock alternator pulley and see how it goes. Will let you know in a couple days.

 

Alright swapped back to the stock alternator pulley. It had 13.9 volts with everything on at its high cold idle of 800 rpm. That seems much better but I will find out for sure when i go to work later. I figured with the underdrive crank/alt pulley combination at idle the alternator was spinning aproximately 700 rpm. With the underdrive crank/stock alt pulley at idle the alternator should be spinning approximately 850.

 

Ya I think you should stick with a stock pully.