World Library  
Flag as Inappropriate
Email this Article

Underdrive pulleys

Article Id: WHEBN0005555144
Reproduction Date:

Title: Underdrive pulleys  
Author: World Heritage Encyclopedia
Language: English
Subject: Fuel saving device, Auto parts, Centrifugal-type supercharger, Turbo fuel stratified injection, Glasspack
Collection: Auto Parts
Publisher: World Heritage Encyclopedia

Underdrive pulleys

An underdrive pulley refers to a crankshaft or accessory pulley (a/c, alternator, power steering, water pump, etc.) designed to turn at a slower speed than stock. To Underdrive means to slow the rate of rotation in a system. Underdrive is achieved by either making the crank/main (drive) pulley smaller or the accessory (driven) pulley larger than the original diameter pulleys.

Underdrive pulleys increase engine output by reducing the draw of the engine's accessories by slowing them down and reducing the HP they use. Horsepower gains from underdrive pulleys can vary by vehicle, engine, number of accessories and the amount of underdrive (Improvements of up to 5-15 HP at the wheels have been seen). Additional and significant performance improvements can be seen by reducing the weight of the pulley versus the original pulley. Gains can range from 3-6 HP per pound of weight reduced.

Poorly engineered underdrive pulleys can cause unwanted side effects; this is due to not spinning the alternator, power steering, and/or air conditioning fast enough. This leads to low alternator voltage, weak/no power steering assist, and weak/no air conditioning effectiveness, especially at idle/low RPM. The most commonly seen result is lighting may dim, or the stereo may cut out. Too much underdrive for a race car is not much of a concern due to the high RPMs they run at, but for daily driven vehicles it can lead to a dead battery if too much time is spend at idle or low RPM.

In addition, changing the original crankshaft pulley can have negative effects if the replacement pulley is not manufactured properly. A crankshaft or accessory pulley not machined or balanced properly can cause severe damage leading to thousands of dollars in repairs.


This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.