Under drive pully
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
You be sure and let us know when the FIRST person with a C6 or C5 has a dead battery from using one. My original C5 battery (2001) is alive and well.
Maybe that should read, I dont have an underdrive pulley so I wonder if it kills batteries.
Maybe that should read, I dont have an underdrive pulley so I wonder if it kills batteries.
Burning Brakes
Joined: Oct 2005
Posts: 1,131
Likes: 0
From: Dallas Texas
Originally Posted by timd38
If you underdive don't complain when the battery goes dead.
Race Director
Joined: Aug 2005
Posts: 13,592
Likes: 187
From: Hudson WI
NCM Sinkhole Donor
Originally Posted by midnite902
Every morning when I start my car my battery is sitting at 14 volts. I have had the UD almost a year
In the last battery return program that one of my engineeers ran, over 45% were discharged only and a smaller pully aggrivates this. This is a very common number and it doesn't really matter what brand of car it is. CAN bus is the best thing that ever happen to the battery business, because it leaves modules on and kills batteries.
You can tell me that I don't know what I am talking about, but I have 4 battery engineers working for me and we make over 110M batteries a year, so I think I have a clue.
Last edited by timd38; Sep 15, 2006 at 05:40 PM.
Team Owner
Joined: Feb 2001
Posts: 27,254
Likes: 136
From: Short Hills, NJ
Originally Posted by timd38
I just spent all day at a car company in Detroit talking about the amount of amperage their cars put out at idle and it is not enough to run the ignition. The car companies have put small pulleys on the alt to reduce noise and improve fuel economy, so if you make it smaller, you increasing the likelihood of not having enough amperage to charge the battery unless you drive the car.
In the last battery return program that one of my engineeers ran, over 45% were discharged only and a smaller pully aggrivates this. This is a very common number and it doesn't really matter what brand of car it is. CAN bus is the best thing that ever happen to the battery business, because it leaves modules on and kills batteries.
You can tell me that I don't know what I am talking about, but I have 4 battery engineers working for me and we make over 110M batteries a year, so I think I have a clue.
In the last battery return program that one of my engineeers ran, over 45% were discharged only and a smaller pully aggrivates this. This is a very common number and it doesn't really matter what brand of car it is. CAN bus is the best thing that ever happen to the battery business, because it leaves modules on and kills batteries.
You can tell me that I don't know what I am talking about, but I have 4 battery engineers working for me and we make over 110M batteries a year, so I think I have a clue.
with this because in a twist of irony shortly after I posted this:
Originally Posted by LS1LT1
I do have one (ASP) on my bolt on Z28 and it has been fine with a full size battery but when running a lightweight (save 22 pounds of the nose) battery it really dimmed the lights even though the idle was bumped up another 50rpm.
) and the brand new, now FULL size battery (to replace my little race battery) that I'd bought 2 weeks earlier was stone cold dead.Not sure if the UD pulley caused it or if I stressed the alternator/charging system too much with the lightweight race battery (which even when letting the car sit for a few weeks without starting never died like this one) over time and now it won't charge as well, I don't know. I jumped it and it did fire back up but I am still concerned.
I might have my idle bumped up a little more maybe.
Melting Slicks
Joined: Jun 2004
Posts: 3,439
Likes: 6
From: Newark, DE
St. Jude Donor '06
Originally Posted by Vette_Fan
I am not understanding this.... 
IF I put on a UD Pulley on my Stock A4, C5 - does that mean I'll have to raise the RPM in idle?
IF I put on a UD Pulley on my Stock A4, C5 - does that mean I'll have to raise the RPM in idle?FWIW, my LS2-based 402 stroker with automatic and mild cam idles at 800/850rpm (AC off/on), and is totally streetable.
Le Mans Master
Joined: Aug 2004
Posts: 5,259
Likes: 16
From: Monroe Township New Jersey
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
St. Jude donor in memory of jpee '14
Originally Posted by SpinMonster
Tommy, you should come down and have a laugh while you hear some new words never heard before by humans as I change it out with RJ (aintqik) this weekend.
What is so hard about cobra longtubes?
What is so hard about cobra longtubes?
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by Mr. Lucky
I think the point of mentioning the raised idle is that this mod is typically done at the same time as a cam swap (because almost the same labor is involved in gaining access to the front of the motor).
I was addressing the silly argument that it spins the alternator slower when you put it on.
So: if the alternator is spinning 10% slower from the pulley and you raise the idle 10% then the alternator now spinning at the same as factory speed?No more slow alternator issue.
I was simply saying there is an easy fix for the guy that thinks its an issue.
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Melting Slicks
Joined: Jun 2004
Posts: 3,439
Likes: 6
From: Newark, DE
St. Jude Donor '06
For anyone seriously considering an underdrive pulley on a totally stock motor that is concerned about the alternator spinning more slowly, there is always the option of simultaneously adding an alternator overdrive pulley (e.g., http://speed-eng.com/store/index.php?cPath=22_49_1052).