I grabbed an '87 iroc a few weeks ago, great condition...yellow from factory and with a 350 . Previous owner said the car had underdrive pulleys and I don't like watching my voltmeter read 9V at idle. I want to return to the stock diameter pulleys but I'm not sure if just the crank pulley was swapped or if a kit was installed. What are the stock pulley diameters (or best way to determine which are stock size and which are underdrive) and what is going to be involved in swapping stock size pulleys back into the car. Thanks in advance.

 

I don't have the exact answer to your question, but most reduction pullies are maybe 20% slower. If you rev your RPMs to 1000 -1200 is it charging full? You could have a feild out in the alternator? That will give you those symptoms at idle, Just a thought...

 

Yeah, it jumps up to 12-13 volts if you rev the engine or pretty much any time other than idle. I haven't had charging problems...alternator seems fine. I just figure the electrical system is designed around 12V, so that's the way I want it.

 

Can somebody give me the stock dimensions of the pulleys (crank, alt, and wp) or tell me where I can find it? I was looking at gmpartsdirect and it comes up with 3 crankshaft pulleys and I'm not sure which particular one is a replacement. I've looked up the different underdrive kits on summit or jegs but they don't seem to list the dimensions of their pulleys either! Not sure that I want to spring $200 for the March Power & Amp kit.

Sitting at a stop light with the fan on, lights&foglights on, radio, etc, my turn signals slow down and voltmeter is very low.