Underdrive Pulleys And Maintenance For Our High-Mileage '03 VW GTI 1.8T Project Car.
Take a look through Readers' Rides (p94) and almost every car has an exhaust, intake and software. Each modification provides a certain amount of power over stock, but ultimately they all reach their limit.
Yet these modifications are integral building blocks to construct your project car. For Project Silverstone, we installed a Techtonics Tuning exhaust shortly after buying the car and haven't looked back since. But now, we'd like to shed light on a relatively neglected yet beneficial modification few new enthusiasts consider - underdrive pulleys.
Pulley BasicsYour engine typically has a series of belt-driven pulleys to turn the accessories that are operated by the crankshaft. Now you might be asking, where can horsepower be gained? The crank's main job is to turn the pistons, but it also powers the pulleys. The idea behind underdrive pulleys is to save some energy by lightening the pulleys and minimizing their diameter. The released energy is translated into more energy to drive the pistons, with less needed to drive the accessories.
Ur SolutionThis idea behind underdrive pulleys has been popular since the muscle car era, and that's when Unorthodox Racing (UR) got started. Since Project Silverstone was still driving without these underrated components, we sought their help.
Shawn Baumgartner at UR revealed the design elements of the 1.8T Ultra SS kit, which he developed on his personal '01 Jetta. "We used a combination of underdrive elements, which is why the 1.8T pulleys are only available in a kit. We didn't want to use stock diameters because we found the accessories are large; primarily the power steering and alternator pulleys. The alternator pulley is almost a clutch, or bearing-type free wheel. Our version weighs less than half the original pulley, making a huge difference." The weight savings with the UR pieces mean the alternator pulley weighs 72% less, the power steering is 42% less and the crank saves 33%.
"From a simple physics standpoint, the motor accelerates quicker because it's driving less on the crankshaft. And the accessories aren't robbing power because the new pulleys are turning them slower," Shawn concluded.
Step-By-StepInstallation was a breeze. We took our project car to Dynamic Racing Solutions (DRS) in La Habra, CA and they quickly removed the factory pulleys and installed the UR pieces in an hour.
ResultsAfter dyno testing the car, we did see fractional gains on the graph; however, we must confess the comparison wasn't exactly fair to the pulleys. That's because our baseline and post-install dynos had to take place on two separate days, and the ambient temperature for the post-install dyno run was a full 10F warmer.
After discussing the results with Shawn, he told us the pulleys will perform better the longer you drive with them.
"The ECU takes time to learn. During the installation, it's best to pull the battery. Give it a week of spirited driving and the computer will eventually learn that weight has been reduced off the crankshaft. But don't worry, some of our customers have reported varying gains. Some are as low as 6-7hp, while others see gains as high as 13-15hp," he told us.
Although our dyno test wasn't ideal, the real test would be on the street. And here, the difference was far more noticeable after driving away from DRS. The new pulleys helped the engine reach boost faster, which improved both daily and spirited driving. Throttle response was more instantaneous and the car felt more responsive through each gear.
Another improvement came in the smoothness of acceleration. This should be credited to the high tolerances designed by UR, which claim to be tighter than factory.
With the combination of the modifications that had already been installed on Project Silverstone, the UR pulleys were certainly worth the time and money invested. We only wish we installed them a lot sooner!
Stay tuned for a final dyno update in an upcoming issue.
1) Raise car and remove four Torx T20 screws to take off lower splashguard. | 
4) Now remove the belt. Pull back on the belt tensioner with a 15mm wrench. This should free the belt | 
5) Using an impact gun with a 24mm socket wrench on a swivel joint, take off alternator pulley. |
6) Raise the car to remove the remaining pulleys. Using a special pulley tool (available at most auto part stores), hold the power steering pulley in place to loosen the 6mm allen nuts. Once all the nuts are cracked loose, the pulley should come straight off | | |