Welcome to the North American Subaru Impreza Owners Club Tuesday April 28, 2015
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Normally Aspirated Powertrain

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 06-19-2001, 09:04 AM   #1
Mikemar
Scooby Newbie
 
Member#: 7259
Join Date: Jun 2001
Location: Western MA
Vehicle:
2004 Sti
Stone Chip Blue

Question Underdrive Pulleys, What do they do??

Sorry for being stupid but, I see a lot of mention of underdrive pulley sets. What purpose do they serve? I think I know where they go but what good does changing a pulley do?
* Registered users of the site do not see these ads.
Mikemar is offline   Reply With Quote
Old 06-19-2001, 09:06 AM   #2
JGard
pooptastic
 
Member#: 1904
Join Date: Jul 2000
Chapter/Region: TXIC
Location: Austin, TX
Vehicle:
2011 BMW X5 35D
01 Miata red

Default

lighter, less rotational mass = easier to turn = more power

also

smaller = easier to turn (think gears on a bike) = more power

now, I should rephrase...because they don't give you more power, rather they rob less from the engine than the standard pulley.
JGard is offline   Reply With Quote
Old 06-19-2001, 09:11 AM   #3
MBX Motorsports
Scooby Newbie
 
Member#: 3726
Join Date: Jan 2001
Location: Newark, DE
Vehicle:
2001 2.5RS
Blue Ridge Pearl

Default

It increases the efficiency of your pulleys, thus requiring less power from the motor to turn them. It doesn't add horsepower, it simply free's some up.
MBX Motorsports is offline   Reply With Quote
Old 06-19-2001, 09:29 AM   #4
Mikemar
Scooby Newbie
 
Member#: 7259
Join Date: Jun 2001
Location: Western MA
Vehicle:
2004 Sti
Stone Chip Blue

Talking Thanky Thanky

Why thanky thanky, Thats what I thoght but they seemed kinda pricey for just lighter pulleys.
Mikemar is offline   Reply With Quote
Old 06-19-2001, 11:30 AM   #5
EchoWrx
Scooby Newbie
 
Member#: 4101
Join Date: Feb 2001
Location: Minneapolis
Vehicle:
2000 Impreza
White

Default Yep!

They are very expensive for what they are but almost worth $150-200 bucks. I know a guy who shattered his stock steel pully on his dual overhead 98 Impreza, now that's torque! He won't use a alloy one because he is scared of doing this again. I have one and I like it a lot. It feels like you have new spark plugs all of the time And it is darn easy to install, if you have big enough tools.
bye
Gill
EchoWrx is offline   Reply With Quote
Old 06-19-2001, 12:02 PM   #6
Poseidon
Scooby Specialist
 
Member#: 4864
Join Date: Mar 2001
Location: North Bend, WA USA
Vehicle:
2004 WRX
Silver

Default

Quote:
smaller = easier to turn (think gears on a bike) = more power
Just FYI, I think you got that a little mixed up. The smaller diameter means that it rotates slower and sends less power to the alternator (or whatever accessory it is driving). This is why they warn that your lights may dim slightly at idle with an UD pulley. Actually, if you take two pulleys (or gears) of equal weight but different diameter, it takes more torque to get the smaller pulley turning. This is why you get a larger HP gain from reducing the pulley weight than you do from reducing the diameter.

Jordan
Poseidon is offline   Reply With Quote
Old 06-19-2001, 12:22 PM   #7
Santo Domingo 2.5 RS
Scooby Specialist
 
Member#: 5354
Join Date: Apr 2001
Location: Santo Domingo. R.D
Vehicle:
2000
Silverthorn Metallic

Question

Do you need to change the size of your belts when you mount an underdrive pulley?
Santo Domingo 2.5 RS is offline   Reply With Quote
Old 06-19-2001, 12:38 PM   #8
Midwayman
Scooby Specialist
 
Member#: 1997
Join Date: Jul 2000
Chapter/Region: MWSOC
Location: Des Plaines, IL
Vehicle:
2006 Acura TL 6spd
STMGM6 alumni

Default

Yes, you need to change the belt size... actually buy one size smaller than they reccomend. UOR likes loose belts or something.
Midwayman is offline   Reply With Quote
Old 06-19-2001, 12:43 PM   #9
RaceCarRiot
Scooby Specialist
 
Member#: 6542
Join Date: May 2001
Chapter/Region: South East
Vehicle:
1997 Ver IV
silver

Arrow

lightened pulleys use the stock belts. underdrive pulleys need different belts, and a decent retailer will usually supply them as part of the package.

i would just go with the lightened pulley, as there's really no disadvantage (lights dimming, etc) to using one...

stock=5 3/4 lb
lightened=1 3/4 lb
i forget what the underdrive pulley weighs, but it's not much less than the lightened one, just a few ounces.

(adam)
RaceCarRiot is offline   Reply With Quote
Old 06-19-2001, 03:12 PM   #10
Santo Domingo 2.5 RS
Scooby Specialist
 
Member#: 5354
Join Date: Apr 2001
Location: Santo Domingo. R.D
Vehicle:
2000
Silverthorn Metallic

Question

Wich company do you think, sells the best Underdrive pulley on the market? and do they come with with the recomended belt size for the new pulley?

ah!! also, how can you lighten the stock pulley by yourse˝f? can this be done?
Santo Domingo 2.5 RS is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Trespassers... What are they doing? What should I do? markman Off-Topic 102 04-08-2008 01:42 PM
Steering bushings....what do they do and how do you know if you need them replaced? kaisersouse Brakes, Steering & Suspension 4 01-11-2006 11:51 AM
What turbos / mods do they do in Japan? Sordid Philosopher Factory 2.0L Turbo Powertrain (EJ Series Factory 2.0L Turbo) 1 06-21-2002 06:56 AM
What do they do for the 10000 mile tune up? WR-REX Texas Impreza Club Forum -- TXIC 3 01-24-2002 12:39 AM
Front/Rear end-links, anti-lift castor's, what do they do? Ru fan New England Impreza Club Forum -- NESIC 7 12-14-2000 12:01 AM


All times are GMT -4. The time now is 08:00 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2015 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.