Many teams choose to run without an alternator. The power needed to run these units is in the range of 1-3 hp. It makes sense to capture all of the available power we can, but does the loss of voltage in the battery make a difference in ignition efficiency? We decided to find out.
Over the past few years, we have run across some teams who, for the goal of attaining maximum power, chose to run without an alternator. We started thinking about that and decided to see if there were any detrimental effects associated with varying levels of input voltage to the ignition system.
There are basically two types of ignition systems in use in stock car racing. There is the inductive ignition in which the current goes directly to the coil and then directly to the distributor. In this system, the magnitude of the output spark is directly proportional to the input voltage. So as the voltage becomes lower, the ignition spark becomes less, reducing the efficiency of the combustion process.
The other system is the CD, or capacitive discharge, ignition in which a capacitor stores electrical energy and releases it to the coil. In these systems, more or less voltage does not affect the magnitude of the ignition spark in a positive or negative way within a certain range.
Our primary focus is on the more popular CD system and how it is affected as the battery voltage becomes low. We thought we might see a negative effect, mainly with the longer races and over the course of an event through practice, heat races, and the main event, if the battery voltage became too low.
The inductive ignition systems should always run an alternator because they are directly affected by the level of input voltage. That means that the output ignition spark at the spark plug is only as intense as the input voltage. A lower voltage input means a less efficient combustion process. Having a topped-off battery means having the most horsepower.
To gain a better understanding of this subject, we consulted with industry experts and even ran an impromptu test at Jay Dickens' facility, where we tried different voltage levels while dynoing a motor. We asked several knowledgeable persons if they knew of anyone who had ever evaluated the relationship between input voltage and ignition efficiency. The recurrent answer was no. That surprised us somewhat. What if there was an effect? Wouldn't that be important to someone who was trying to decide whether or not to run an alternator?
This high-energy ignition system from MSD is a very popular unit for some applications. The inherent design of these types of ignition systems causes them to be more dependent on the correct voltage input. So the output charge is directly affected by the input voltage. For these units, we recommend always running an alternator.
WHAT THE EXPERTS SAY
Our first call was to Todd Ryden with MSD Ignition. We discussed the various types of ignition systems and how they might be affected by varying voltages associated with the absence of an alternator to replenish the battery power.
He told us that MSD had not run any tests of its own, but believed that the ignition output for the CD ignition, such as the MSD HVC-L unit, would be consistent over a wide range of voltages. "If we ran a 16-volt battery, we would see no increase in combustion efficiency and horsepower output over using a 12-volt battery," Ryden explained. In other words, the units keep the output consistent even though the input is not.
What does happen with a CD ignition system is that once the battery output goes below a certain voltage, the ability to release a substantial charge is affected and the system may not operate correctly.
We also spoke with Paul Lundquist, who runs MG Industries, a manufacturer of racing starters and high-output alternators. His take is that running without an alternator "is the wrong way to go." He brings up the matter of additional battery drain from using electric fans and fuel pumps, but his references are mostly concerning the inductive ignition systems.
On those systems, horsepower drops of 3 to 30 hp are not uncommon due to low voltage levels. The direct-induction ignitions are typi-cally designed to be used with 14.0 to 14.8 volts of input for maximum efficiency.
We installed a new MSD HVC-L ignition box in our NASCAR Late Model stock car. A rev limiter is included in this variation of the popular HVC unit. The rpm limit is adjustable with plug-in modules.
TESTING ON THE DYNO
Jay Dickens, an engine builder and contributor to Circle Track, ran a test at our request in which he dyno'd a high-horsepower dirt Late Model motor in phases. He was asked to try to find differences in horsepower as the battery that ran the ignition system was discharged.
The initial base run was done, as is customary in his shop, with a fully charged battery and a charging system attached to the battery. This ensured a full and consistent voltage output to the MSD 6ALN ignition system that was in use.
Once the horsepower curve was established, a battery was attached just to power the ignition system and not start the motor. This battery was not aided by a charging system, either. That battery was slowly drained after each run and the engine horsepower levels were noted. The first run was at 13.6 volts, and then backup runs were at 12.8 and 12.1 volts.