When the next dyno pull was run at 11.4 volts, the motor started running rough. A further drop in voltage to 11.1 volts caused even more disruption in the firing of the motor, and the run was stopped to avoid hurting the motor. It would seem, according to this test, that when the battery reaches a level of less than 11.5 volts, the motor will not only begin to lose power and run erratically, but also may cause damage to engine components.
This correlated somewhat with what Todd had told us. He predicted a drop to 9 to 10 volts would cause problems, but the threshold appears to be a bit higher. The CD ignition works the same through different levels of voltage unless it drops to a certain level-then the system will not function properly. This is understandable. At least we have a consistent output through a wide range of voltage levels with the CD system.
The following recommendations are based on our research and the information we received:* Don't run without an alternator if you're using an inductive ignition system such as an HEI or something similar.* If you're planning on running without an alternator, you need to install an accurate voltage meter so you can monitor the voltage levels in your battery.* It might be a good idea to run two batteries. With the modern, small, light battery packages (such as the Dyna-Batt we run in our Late Model stock car), running two batteries is not a weight disadvantage. The battery box in our car is built for a standard-sized battery and will easily hold two of these smaller batteries. Then you can install a battery switch similar to the ones used on boats and, if need be, switch bat-teries when the voltage gets low.* Another idea would be to run the accessories off a separate battery from the engine/ignition system's main battery. Things such as the electric radiator fans, electric fuel pumps (if you use one), as well as the starter all draw lots of amps to deplete your battery.* Always charge your battery whether you run an alternator or not. When the car is in the pits between practice sessions and while waiting for the start of the race, charge that battery. There are cheap charging systems available that could be installed in place of some of the ballast weight (so you're not adding weight to the car). These units trickle-charge the battery and have an automatic shutoff when the battery is fully charged. Along with a recessed male 120-volt plug, you could run an extension cord to the car and easily plug it in when the car is not on the track and even when it's in the shop.
CONCLUSION This was a fun exercise and one which we think broke ground somewhat. We don't like unknowns for any system on the race car, and when we were trying to decide whether or not to run an alternator on our own Late Model stock car, we decided to investigate a little further.
The last thing you or I need when we get in the position to win is for our ignition system to break down. So we think it's a fair trade-off to give up the 2 or 3 horsepower and gain a lot of reliability. That's our decision and we're sticking to it.