Problem:
After installing a 3-piece set of March underdrive pulleys, the voltage has dropped quite a bit and it almost goes into the red with headlights, and brake lights on. The blinkers are way too slow too.

I know this is expected since the alternator speed has dropped. The engine idles at 500 RPM and the minimum idles speed is set for 450 RPM (on "drive"). I have taken a reading at the battery and it reads 11.5V at idle, and another reading with the lighter plug-in meter reads at 12.2V at idle. Revving the engine to just over 650RPM will rise the voltage to well over 13V.
March does recommend rising the idle speed if the volt gage goes in the red. I plan on rising the minimum idle to 600RPM to keep the voltage out of the red.

My question is, if I change the minimum idle speed to 600, should I reset the TPS back to the recommended setting or should I leave it.

Any thoughts?

 

I have been through this problem on both of my Camaros & found that it is hard on both alternators & batteries. The solution is to install an overdrive (smaller diameter than stock) pulley on the alternator to return the crank to alternator ratio to the stock 3.4:1 value. Installing an underdrive (larger diameter than stock) pulley on the alternator & an under drive (smaller diameter than stock) on the crankshaft puts the ratio at 2.2:1, which is too low for driving accessories at idle on a daily driver.

------------------
Tim

1992 Z28, 305 TPI 5 speed, 12.0 sec @ 114.8 mph

1984 Berlinetta 305 TPI Auto, 13.8 sec @ 99.7 mph

 

Thanks Tim. I guess some things you have to find out the hard way. Anyways I did put the stock pulley back on the alternator and it brought the voltage back up to 13V with accessories on. The underdrive pulley that I got with the kit from March was just as you said, somewhat bigger than stock. No matter what I did the voltage still dropped.
The problem is solved and it looks like I will keep the stock pulley on.
Thanks,
Ozzy

PS. Others looking into buying the 3 piece set should be aware of this problem. March also offers the Power and Crank set which as advertised is supposed to retain cooling and charging characteristics. That might be a better choice.

------------------
My GTA
1988 GTA, 5.0 TPI, TH700-R4, marron w/black