Starter Basics from Powermaster Performance

(More tech articles on the Tech, Tests & Installs page HERE)

Publisher's note: I was on the website of our friends at Powermaster Performance, makers of racing alternators and starters, and saw this very informative article that I thought would be helpful to share with you here.


CHOOSING A STARTER

1) Torque Requirements

The torque output of a starter is the most important consideration. The starter must be able to spin the engine, and do it without overheating internally. Since there is no such thing as having too much torque -even on a street vehicle - a 200 ft.lb. starter will work for everyone. Speaking in general terms, a over 12:1 compression or higher engine should use a 200 ft.lb. starter. Engines up to 12:1 should use at least a 180 ft.lb. starter. 160 ft.lb. starters are good for engines up to 10.5:1.

One thing to keep in mind is that the torque characteristics of a starter are a function of its design. High voltage batteries or low internal resistance batteries will affect the kilowatt output of the starter by changing the output speed but not the torque. Therefore, buy enough torque to begin with.

2) Fit

Of course for a starter to work, it must fit the application. Consider headers, oil pans, and the mounting points on the engine. What size ring gear do you have (for Chevy applications)? Does your Chevy block accommodate a straight mount starter, or is the only pattern drilled in the engine block for a diagonal or offset pattern starter? In racing, did the oil pan manufacturer lock you into a particular shape of starter? In your Ford application, is your ring gear 3/8” from the engine plate - indicating a typical manual transmission starter - or is it closer to a 3/4” - requiring a typical auto transmission unit? How tight are the headers around the starter? These are just some of the questions that will help you determine the right starter for your application.

3) Weight

Lastly, depending on the form of racing, the overall weight of the starter is a consideration.

TORQUE DEFINED:

Torque is the ability to overcome rotational resistance. High compression, large displacements, tight rings, blowers, and other factors all offer rotational resistance - and it takes torque to overcome this. Unfortunately, starters are rated in kilowatts. This is a measure of its torque and speed combined. The torque output is really unknown.

Starters, like engines, have different powerbands. Some have a maximum power point at a relatively high RPM with little torque. Whereas others produce more torque and yet lower RPM. In the performance environment, torque is the most important consideration, generally because a performance engine offers more rotational resistance than stock. As a result, kilowatt ratings can be confusing because two starters with the same kilowatt rating can have very different torque characteristics.

The engine will demand a certain amount of torque for cranking. When the torque demands cause a starter to exceed its maximum power point, the extra input energy is wasted as internal heat. Asking a starter to produce more torque than it is comfortable with results in low electrical to mechanical efficiency and drastically increased internal heat. This is what causes premature starter failure. The key is to use a starter that has a power peak at a high torque point. Then, in the event that the cranking conditions offers high resistance, the starter will have the torque characteristics to handle it without overheating.

Several other factors effect starter performance dramatically. Voltage is very important. Cabling and quality disconnect switches are important because under heavy load, voltage will be lost or "dropped" in undersized or hot cables, or hot switches. The internal resistance of the battery itself results in decreased voltage to the starter. Therefore, low internal resistance batteries like typical 1000CCA - or better yet - spiral cell AGM batteries such as Optima and others should be used. High voltage batteries like the new 16 Volt Powermaster battery is a perfect choice for any racing application.

When you purchase a Powermaster starter you will get a dyno sheet that shows you the exact performance of your starter. The sheet itself will explain how to interpret the data, but you can be assured that Powermaster starters are built to a consistent, statistically controlled standards, and that they are dynamically tested throughout their entire power range.

Source:
Powermaster Performance
www.PowermasterPerformance.com