Spin Control: Why Alternator Pulley Ratio Is Important

You need an alternator for your ride, so you should be able to just buy one that matches the year/make/model, right? Well, not exactly, because you need to look at the pulley ratio for your particular application to ensure the alternator is functioning properly. We talked with the team at Powermaster to learn more about alternator pulley ratios.

The alternator pulley ratio is something that most people don’t consider when they’re putting the finishing touches on a build. What you need to keep in mind is that an alternator has a rpm sweet spot where it optimally functions. If you spin the alternator harder than the optimal rpm level it won’t increase output, it could actually damage the alternator. On the other end of the spectrum, if the alternator isn’t being spun hard enough, it won’t be able to produce the correct amount of current to charge your battery.

So, what is pulley ratio? Pulley ratio is the comparison of the crank pulley diameter with that of the alternator pulley. You calculate the ratio by dividing the crankshaft’s pulley diameter by the diameter of the alternator pulley.  Here’s a basic example: a 6” crank pulley used with a 2” alternator pulley comes out to a 3:1 ratio.

When you push an alternator to its max rpm there will be a lot of heat, it won’t be efficient, and the bearings are at their limit. So, if you’re revving and running your engine at high rpm, you might want to think about moving to a larger alternator pulley to slow it down. You can apply that logic to a vehicle that sees a lot of street driving, and use a smaller pulley to keep the alternator in its happy place for optimal current generation.

Make sure you’re doing the simple math to find the best alternator pulley size for your application. By doing this your alternator will last longer, and it will produce the correct amount of juice to keep your battery charged.

Article Sources

About the author

Brian Wagner

Spending his childhood at different race tracks around Ohio with his family’s 1967 Nova, Brian developed a true love for drag racing. Brian enjoys anything loud, fast, and fun.
Read My Articles

Drag Racing in your Inbox.

Build your own custom newsletter with the content you love from Dragzine, directly to your inbox, absolutely FREE!

Free WordPress Themes
Dragzine NEWSLETTER - SIGN UP FREE!

We will safeguard your e-mail and only send content you request.

Dragzine - Drag Racing Magazine

We'll send you the most interesting Dragzine articles, news, car features, and videos every week.

Dragzine - Drag Racing Magazine

Dragzine NEWSLETTER - SIGN UP FREE!

We will safeguard your e-mail and only send content you request.

Dragzine - Drag Racing Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...


Street Muscle Magazine
Hot Rods & Muscle Cars
Diesel Army
Diesel Army
Engine Labs
Engine Tech

Dragzine - Drag Racing Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • Streetmuscle Hot Rods & Muscle Cars
  • Diesel Army Diesel Army
  • Engine Labs Engine Tech

Dragzine - Drag Racing Magazine

Dragzine

Thank you for your subscription.

Thank you for your subscription.

Dragzine - Drag Racing Magazine

Thank you for your subscription.

Thank you for your subscription.

Loading