So... I have a GM style one-wire alternator. Prior to this year, I had observed that my alternator wasn't charging below 2000 rpm. I have a fairly small crank pulley, so I had a friend machine me a smaller alternator pulley, and tested the voltage. Before my first outing this season, the battery was showing 13+ volts at idle with the engine, fuel pump, and water pump running. The cooling fan has enough draw to pull it to a discharge at idle, but at 1000 and up, it was now charging. I could never figure out why I couldn't get more than a few rounds out of it before needing to charge up, given that I assumed it was charging the battery, when I was actually discharging even chugging down the return road at 1500-2000 rpm. So, I changed the pulley size.
That seemed to fix it until the last weekend at the track. One pass on a fully charged battery brought it down to 10-11 volts by the time I got back to our pit stall. We spent both days chasing an electrical demon while going rounds. Thinking my battery had cratered, I installed a new one. (Thankful for the New Holland implement dealership within sight of the track.) No dice. Another racer lent me his alternator. Still didn't fix the issue. Back home, I bypassed the existing wire from the positive side of the alternator to the battery. No change. I traced the power feed from the kill switch that goes back to the MSD box, and repaired what I thought might have been a chafed wire that could have been grounding to the chassis. A quick fire-up led me to think that might have been the issue.
Tonight, I threw the timing light on it, and starting with a fully charged battery and running it with the fan and water pump running to keep it cool, I was out of battery within a few minutes. Before I could set the timing and lock it in, the car was having difficulty just idling due to lack of juice. When I shut it off, the battery had enough juice to spin the fan, but not crank the engine over.
When the battery is good, this thing fires at the touch of the button, but it devolves with loss of voltage.
I'm sure something simple is staring me in the face, but what? I'm beginning to think the voltage issue might be the key to my absence of power. I'm not getting how it's killing a battery in one pass, either. I've been under the impression that a good RV/Marine battery could sustain a set-up like mine without an alternator and simply externally charging between rounds, and I know this will barely get me from the pits to the lanes, let alone a full pass and drive down the return road.
