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The Pros & Cons of Underdrive Pulleys

are underdrive pulleys worth it

When you think of underdrive pulleys, you might think of muscle cars and hot rods. Underdrive pulleys have been used in vehicles since the 1950s and were even used on the Ford Mustang. Today, Underdrive pulleys are a terrific choice for vehicles that don’t require a lot of electrical power to make passes, like track cars.  Even if you don’t drive a race car, underdrive pulleys are useful for big power gains and high throttle response, all while maintaining your charging system. 

When it comes to modern mechanics and machinery, are underdrive pulleys worth it? Read on to learn the latest from the experts at Illinois Pulley & Gear. 

How do Underdrive Pulleys Work? 

In modern muscle cars, a crankshaft pulley drives a serpentine belt, which in turn powers the car’s accessories, including the air conditioning, water pump, alternator, and power steering. The underdrive pulley’s purpose in all of this is to slow down the accessories. The underdrive pulley essentially uses a small diameter crankshaft pulley, decelerating the serpentine belt. The intended effect of an underdrive pulley is a reduction of parasitic power loss on the engine.

Are Underdrive Pulleys Worth it? 

When it comes to deciding whether to use an underdrive pulley in your car (or another machine), it’s important to weigh the pros and cons. Some of the pros of underdrive pulleys include power savings and substantially reduced belt and component wear. 

The cons? Power reductions, the potential for overheating, and low voltage that may conflict with some of your car’s high-energy aftermarket additions. Below, we elaborate on what the modern mechanic will want to consider.

The Pros of Underdrive Pulleys: 

  • Power Savings: The larger the diameter of the accessory pulley, the lower RPM you’ll get in return. When you use an underdrive pulley, you can make major horsepower gains. Because they replace stock water pumps, power steering, AC units and alternators, you may even notice increased acceleration when you choose an underdrive pulley. 
  • Substantially Reduced and Component Wear: Mechanics love underdrive pulleys for their ability to go easy on the belt and the car’s components. Belt wear is substantially reduced when you make the switch to an underdrive pulley, in large part because of reduced rotation: the belt simply doesn’t make as much contact with pulley guides. Your belt might even outlast its expected lifetime. 
  • Substantially Reduced Component Wear: In the same vein, the use of underdrive pulleys in vehicles leads to much lower wear on other components, including the clutch, water pump, alternator, power steering pump, bushings, sealed bearings, and shafts. 

The Cons of Underdrive Pulleys: 

  • The Potential for Power Reduction: If your vehicle needs a ton of power, you may want to take a closer look at the drawbacks of using an underdrive pulley. With an underdrive alternator pulley, all components and accessories will be running at the same time. This can lead to a voltage drop in the charging system. 

You may notice your battery draining faster and dimmer headlights, among other concerns. This is due to the alternator simply not spinning fast enough to provide power to all accessories. All told, the potential for power reduction is certainly something to consider. 

  • The Possibility of Overheating: Adequate cooling is a serious concern for mechanics. It’s good to keep in mind that when you replace a water pump with an underdrive pulley, you may be in for a reduction in the speed of the water pump impeller, which will then slow the flow of coolant to your car’s engine. This is something to watch out for particularly if your cooling system has a clog or a leak. 
  • Imperfect Compatibility with Your High Energy Add-Ons: Have you installed after-market modifications, like an electric cooling pump, stereo amps, and high-powered speakers, modified ignition systems, racing spark plugs, or high output coils? You may have foreclosed the possibility of your vehicle’s compatibility with an underdrive pulley. 

Remember that underdrive pulleys produce comparatively lower voltage, and you likely need high voltage to run your add-ons.   

We’re all attracted to the prospect of underdrive pulleys for their power savings and wear reduction. Installing one can be the right move if your car doesn’t need super high amounts of electrical power. 

Want to learn more about choosing the right pulley for your project? Reach out to the experts at Illinois Pulley & Gear. 

Work with the Pulley Experts and Bring Illinois Pulley & Gear’s Full Range of Capabilities to Work for You. 

Timing Belt Pulleys:

Are you searching for the right timing belt pulley to fit a specific need? We commonly work with manufacturers looking for customized equipment. At Illinois Pulley & Gear, we make made-to-order timing pulleys that can be produced to any customer specified requirements, including pitch, number of teeth, bore size (English or Metric), keyway, setscrews, lightening holes, and timing marks. 

Timing Pulley Stock:

Timing pulley stock is the standard material used to create custom timing pulleys. Stock is often utilized for prototyping, experimentation, or crafting replacement parts. We manufacture a large variety of high-quality timing pulley stock made on-demand in the USA. 

Our process allows us to precision machine virtually an unlimited variety of timing pulley stock. Our customized timing pulley stock is made according to your specifications, including the material, tooth profile, and number of teeth you need. 

Pulley Replacement Parts:

Stainless steel, plastics – anything is possible. Specific pulley replacement parts can be challenging to find, whether the OEM is out of business, the part is out of stock, the machine’s manual is missing, or the item is simply too old to be produced. 

At Illinois Pulley & Gear, acquiring pulley replacement parts is made simple. We receive your part and reverse-engineer the product within a matter of days. 

Our Service:

Are you looking for plastic or stainless-steel stock or a unique grade gear commonly unavailable? Our client-oriented team is ready to comprehend your specific needs and provide innovative solutions.  Our quick turnaround time is designed for manufacturers in need of immediate, specific solutions – within a matter of days. 

At Illinois Pulley & Gear, we promise uncompromised service. Our team is dedicated to every client, readily available to connect over the phone, help solve problems, and answer questions. As a client-oriented company, we are ready to listen well, comprehend needs, work through issues, and provide innovative solutions.  Our team is flexible to accommodate your requirements. Place blanket orders for the entire year or order as needed – we are ready to meet your specific needs. Contact us today to learn more.

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The Pros & Cons of Underdrive Pulleys

When you think of underdrive pulleys, you might think of muscle cars and hot rods. Underdrive pulleys have been used in vehicles since the 1950s and were even used on the Ford Mustang. Today, Underdrive pulleys are a terrific choice for vehicles that don’t require a lot of electrical power to make passes, like track…

  • Illinois Pulley & Gear has provided precision machining services for us for over 5 years.  They have been consistently reliable, professional, and flexible from quoting to manufacturing and delivery.
    Eric BroseProject Manager, Technico Precision Manufacturing, Inc.
  • Illinois Pulley and Gear has been amazing to work with. They produce high-quality, custom parts, and they know their business.
    MattProject Manager,

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