ZZP Underdrive Pulleys

I figured I’d make a post for anyone who was curious about doing this mod. Underdrive pulleys work by slowing the rate of the accessories and reducing rotational mass (they are significantly lighter). This allows more of the engines power to go to the rear wheels. ZZP claims 3rwhp at 6,000 RPM for the 14% reduction water pump pullley on a stock engine and slightly more on a modified setup. It doesn’t claim a gain for the 10% reduction alternator pulley. I got both the water pump and alternator pulleys. I’m guessing I might have gained between 5-10 hp since its a bolt on/tuned car. If you only get one of the pulleys, you can use a stock sized belt. If you get both like I did, you’ll need a size 150 belt.

The install:

  1. Disconnect the negative terminal on the battery.
  2. Loosen the 4 bolts on the water pump pulley with the belt still tensioned
  3. Loosen the bolt on the alternator (this will be difficult without an impact wrench)
  4. Twist the bolt on the tensioner pulley to make it swing down in order to remove the belt.
  5. Remove the belt and the stock pulleys.
  6. Install the water pump underdrive pulley and tighten the 4 bolts by hand.
  7. Do the same for the alternator pulley bolt.
  8. Install the new belt (or stock belt) and follow the belt routing guide on the inside of the engine bay.
  9. Tighten the water pump pulley bolts.
  10. Tighten the alternator pulley bolt to spec. (again, a torque wrench would come in handy)
  11. Reconnect the negative battery terminal.

Alternator pulley – $50.00
Water Pump Pulley – $70.00
Serpentine Belt – $32.00
Spending all this to get 5-10 horsepower out of your v6 – Priceless

Note: I installed a new alternator at the same time so what I did was take my new alternator to a shop and have them torque the pulley on there. You could do the same with the stock alternator if needed. Its really easy to remove and most shops would do it for free because its so quick and easy.

Results: I noticed slightly quicker revs and more torque throughout the power-band from this mod. The car chirps shifting from 1st to 2nd at WOT a lot more than it used to (pretty impressive for an auto) which is one thing that really stood out to me. Overall I am pleased with it for how simple it was although it was somewhat expensive for everything.

Stock pulleys:

Underdrive pulleys:

Some new engine bay pics:

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