[Bill Harris]

From a battery perspective, a lot depends on whether you have a functional alternator and if you always put it on a charger in the pits. A little battery like a group 35 Optima red-top at 31 lbs would certainly start the engine with good cabling, but how many times? I have always had two batteries in my racecars, and a functioning alternator, but I still worry about having to start the damn thing 10 times while moving up in the staging lanes. If you don't have a working alternator, and have drained the battery before staging the car, it might not have the capacity to properly run the ignition system during the run, much less start the engine after the scales or fuel check.

As for the cables and connections, just keep one thing in mind. At high amperages like those associated with a starter, very small resistances can result in large voltage drops. Automotive electrical systems are plagued by having to deal with a relatively low voltage and therefore you have to deal with a lot of current if you have to supply a lot of power (hence the 16V batteries that are out there). The ear-bleeding car stereo whackos are very familiar with this situation and have developed some pretty good electrical stuff to deal with multiple 1000W power amps and such which have to work off 12V.

So lets say you cheap out an use that old battery shutoff switch you have laying around. You wire your car in a way that all current from the battery goes through the cutoff switch which is the usual (and legal) way of doing things. Say the switch has 0.01 ohms of resistance. In general, 0.01 ohms is a very small amount of resistance. You probably couldn't read that low value on the usual cheapo volt-ohmmeter, it would just say zero. Assume all the other connections are perfect. That stinking little 10 milli-ohms of resistance is going to drop 150*0.01 = 1.5V all by itself, reducing your 12V to 10.5V at the starter. But now if you need the full 1.9HP from the starter to crank the engine it will take 173 Amps at 10.5V with the additional current dropping the voltage even more... and so on. You can tell that the switch is a POS since it will get hot. If it drops 1.5V at 150A it will be dissipating 225 watts, more than two 100 watt light bulbs, and you know how hot a light bulb can get. If your cut-off switch is even warm, it should be in the garbage.

The point is that it is absolutely imperative to make the best electrical connections you can possibly make when you have to carry a lot of current. Tiny amounts of resistance can cause huge differences in the ability to deliver power to the intended load (the starter motor).

For your 4 foot cable length, a 6 gauge cable will present around 410 micro-ohms, which has a voltage drop of 0.0615 volts at 150 amps, well within the "don't care" region. A 4 gauge is about half as much. That is all hunky-dorey, as long as the connections between that cable and the battery and starter are very, very small resistances too, and that is where the problems can arise. If you crank your engine over for a few seconds and then touch the cables or cable connections and they are hot, or even warm, you have a problem.

One area that people forget is the "ground" path. If you are supplying 150A from the battery to the starter motor, then 150A has to go back from the starter motor to the battery. There are two current paths to deal with, not one. Remember that strap from the cylinder head to the firewall that you didn't bother to put back on because it was a pain? Put it on. Even with solid motor mounts and a torque strap, use a good large gauge strap between the engine and the chassis. Solid motor mounts are mechanically solid, not electrically solid. The starter is probably the highest current draw you will encounter in a race car. Run the same sized cable from the starter to the chassis as you do from the solenoid to the battery, then make sure that the negative side connection from the battery to the chassis is excellent, nothing less.

Can you tell that I'm still bored?