Ignition Amp Use

RPM (V8 Powerplant)	MSD 6 & 7 Series
3,000	3
4,000	4
5,000	5
6,000	6
7,000	7
8,000	8
9,000	9
10,000	10
11,000	11
12,000	12

The following is a sample racecar Ah draw. As you can see, it's a pretty simple car. In the example, pretend the engine sees a maximum RPM ceiling of 8,000 RPM.

• Electric fuel pump: 8 amps
• Electric water pump drive: 5 amps
• Other accessories: 5 amps
• Ignition requirements: 8 amps

  Total: 26 amps

Multiply the total electrical requirements by the duration of time it must operate without a battery recharge. This is particularly important for racecars without charging systems. Keep in mind that we're not talking about seven to ten seconds in this case. Consider the time you "hurry up and wait" in the staging lanes, the time to make a burnout, time to stage, driving down the return road and so on. In this case, a safe figure is 1/2 hour maximum. Multiply the amp requirement by the time:

26 amps X 1/2 hour = 13 amps

Now, the final step in the equation (and one which might surprise you): Starting the car. To determine just how many amps it requires to start the car, multiply the final amp requirement figure by a factor of 3:

13 amps X 3 = 39 amps

The final 39-amp number is the size of battery required for your application. Using the very first equation that showed how to convert RC (reserved capacity) to Ah, you can then go battery shopping.

What Batteries Are Right?

There are a number of batteries that work in drag race applications. The trouble is, once you get deeper into the rounds of competition, the time between rounds obviously decreases. That's precisely where the advantage of a 16-volt system enters the equation.

16-volt batteries are more common in drag racing than you might think. A typical lead/acid battery produces a maximum of 2.1 volts per cell open circuit or 12.6 volts total. As soon as a load is placed on a 12-volt battery, the voltage per cell will rapidly drop to 2.0 volts per cell or 12 volts total. Operating below this voltage level can cause ignition problems such as a high- speed miss. Reduced voltage will also negatively affect the starter along with the ability to spin the engine.

Typical racing ignition systems in use today require at least 12 volts to produce an optimum spark. A lead/acid battery cell (flooded cell, gel-cell, or starved electrolyte) produces a maximum of 2.1 volts per cell open circuit or 12.6 volts total. As soon as a load is placed on a 12-volt battery, the voltage per cell will drop to 2.0 volts per cell or 12 volts total. Operating below this level often results in ignition problems such as a high speed miss. Reduced voltage will also negatively affect the starter and it's ability to spin the motor.