under pully???
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
It is a new crank pulley that drives the accessories a little slower. Supposed to help with performance but you won't feel the difference. Better used to replace the stock unit when it fails.
Be careful of the underdrive if you expect to drive in hot weather at night and idle or cruise slowly - such as getting stuck in traffic on the way home. The lights, AC and cooling fans running will slowly drain the battery. The temps will climb also due to slower water pump speed and less voltage due to alternator running slower which then means the cooling fans run slower. It doesn't matter how much and under drive pulley is pushed as great, the car can't function as well if you start taxing your cooling and electical system since the cooling and electical system are going 25% slower.
I almost overheated in a traffic jamb one night. Had to go AC off and windows down to keep it under 250. It just stabilized enough to reach an exit where I could run down a few streets with a little rpm and some speed to get the temps down and the voltage back up.
Be careful of the underdrive if you expect to drive in hot weather at night and idle or cruise slowly - such as getting stuck in traffic on the way home. The lights, AC and cooling fans running will slowly drain the battery. The temps will climb also due to slower water pump speed and less voltage due to alternator running slower which then means the cooling fans run slower. It doesn't matter how much and under drive pulley is pushed as great, the car can't function as well if you start taxing your cooling and electical system since the cooling and electical system are going 25% slower.
I almost overheated in a traffic jamb one night. Had to go AC off and windows down to keep it under 250. It just stabilized enough to reach an exit where I could run down a few streets with a little rpm and some speed to get the temps down and the voltage back up.
Last edited by lionelhutz; Mar 21, 2012 at 01:13 AM.
Thread Starter
Burning Brakes
Joined: Feb 2011
Posts: 776
Likes: 1
From: spring tx
It is a new crank pulley that drives the accessories a little slower. Supposed to help with performance but you won't feel the difference. Better used to replace the stock unit when it fails.
Be careful of the underdrive if you expect to drive in hot weather at night and idle or cruise slowly - such as getting stuck in traffic on the way home. The lights, AC and cooling fans running will slowly drain the battery. The temps will climb also due to slower water pump speed and less voltage due to alternator running slower which then means the cooling fans run slower. It doesn't matter how much and under drive pulley is pushed as great, the car can't function as well if you start taxing your cooling and electical system since the cooling and electical system are going 25% slower.
I almost overheated in a traffic jamb one night. Had to go AC off and windows down to keep it under 250. It just stabilized enough to reach an exit where I could run down a few streets with a little rpm and some speed to get the temps down and the voltage back up.
Be careful of the underdrive if you expect to drive in hot weather at night and idle or cruise slowly - such as getting stuck in traffic on the way home. The lights, AC and cooling fans running will slowly drain the battery. The temps will climb also due to slower water pump speed and less voltage due to alternator running slower which then means the cooling fans run slower. It doesn't matter how much and under drive pulley is pushed as great, the car can't function as well if you start taxing your cooling and electical system since the cooling and electical system are going 25% slower.
I almost overheated in a traffic jamb one night. Had to go AC off and windows down to keep it under 250. It just stabilized enough to reach an exit where I could run down a few streets with a little rpm and some speed to get the temps down and the voltage back up.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
You also have to remember that the part is actually a harmonic damper for the crankshaft and some of the aftermarket units have been linked to timing chain failures, most notably the ASP underdrive pulley. Replacement by itself is a lot of work for minimal increase in HP, however if you have the stock unit off for other reasons that is a good time to consider a swap. When you do, choose wisely when selecting a new one.
Team Owner
Joined: May 2001
Posts: 36,836
Likes: 244
From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
You also have to remember that the part is actually a harmonic damper for the crankshaft and some of the aftermarket units have been linked to timing chain failures, most notably the ASP underdrive pulley. Replacement by itself is a lot of work for minimal increase in HP, however if you have the stock unit off for other reasons that is a good time to consider a swap. When you do, choose wisely when selecting a new one.
Good advice. Like anything else, you need to shop around, get recommendations, etc from reputable sources. It should be a part of a balanced (NPI) approach or package of mods, not just a separate thing. Companies like ATI, Powerbond, Innovators West, SLP, etc all have excellent feedback and good reputations earned over the years. They are not the snake-oil or boogey-man some would have you believe and they are damned well better than the stocker, if for no other reason than to get rid of the high-failure-rate stocker with that dumb torque-to-yield crank bolt with no crank-pin or keyway. When you get one, pin the crank and use an ARP crank bolt. HTH
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
Driving on a hot night in a traffic jamb with the AC and lights on = problem.
Driving around on a Sunday afternoon without the lights = no problem
How do you drive your car again?
As I posted, an aftermarket pulley is better to use as a replacement for the stocker than to say it's a performer improver.
Driving around on a Sunday afternoon without the lights = no problem
How do you drive your car again?
As I posted, an aftermarket pulley is better to use as a replacement for the stocker than to say it's a performer improver.
Team Owner
Joined: May 2005
Posts: 23,682
Likes: 9
From: Flagstaff Az.
It is a new crank pulley that drives the accessories a little slower. Supposed to help with performance but you won't feel the difference. Better used to replace the stock unit when it fails.
Be careful of the underdrive if you expect to drive in hot weather at night and idle or cruise slowly - such as getting stuck in traffic on the way home. The lights, AC and cooling fans running will slowly drain the battery. The temps will climb also due to slower water pump speed and less voltage due to alternator running slower which then means the cooling fans run slower. It doesn't matter how much and under drive pulley is pushed as great, the car can't function as well if you start taxing your cooling and electical system since the cooling and electical system are going 25% slower.
I almost overheated in a traffic jamb one night. Had to go AC off and windows down to keep it under 250. It just stabilized enough to reach an exit where I could run down a few streets with a little rpm and some speed to get the temps down and the voltage back up.
Be careful of the underdrive if you expect to drive in hot weather at night and idle or cruise slowly - such as getting stuck in traffic on the way home. The lights, AC and cooling fans running will slowly drain the battery. The temps will climb also due to slower water pump speed and less voltage due to alternator running slower which then means the cooling fans run slower. It doesn't matter how much and under drive pulley is pushed as great, the car can't function as well if you start taxing your cooling and electical system since the cooling and electical system are going 25% slower.
I almost overheated in a traffic jamb one night. Had to go AC off and windows down to keep it under 250. It just stabilized enough to reach an exit where I could run down a few streets with a little rpm and some speed to get the temps down and the voltage back up.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
Ummm NO! 250 is well over the high fan on temperature without the AC so both fans were running at rull speed.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
All provide harmonic damping, however there is a question to the effectiveness. ATI is the "go to" company for racing and high demand motors including the C5R, etc. I went with the ATI 10% under drive after spending time speaking with one of their engineers at Carlisle several years ago.
Team Owner
Joined: May 2001
Posts: 36,836
Likes: 244
From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
