Underdrive pulleys
Thread Starter
Instructor
Joined: Jun 2002
Posts: 218
Likes: 0
From: Winnetka CA
Underdrive pulleys
Do underdrive pulleys significantly lower alternator and AC output? Also, how much power gain do they provide?
I ask because my voltage output is pretty low, and even lower with the AC running. It is so bad that if I drive around town all day with the AC on, the battery will not charge enough to be able to start the car back up. The alternator is brand new and the battery has been tested, so the only thing I can figure is that the alternator can't keep up with the power drain from the AC blower, but I dont know...
I ask because my voltage output is pretty low, and even lower with the AC running. It is so bad that if I drive around town all day with the AC on, the battery will not charge enough to be able to start the car back up. The alternator is brand new and the battery has been tested, so the only thing I can figure is that the alternator can't keep up with the power drain from the AC blower, but I dont know...
Team Owner
Joined: Sep 2001
Posts: 62,153
Likes: 1,731
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Some would say 'around' 10hp, and some would say zero. I believe they would help, but I dont like the idea of the alternator spinning slower.
Le Mans Master
Joined: May 2000
Posts: 7,033
Likes: 12
Running pulleys on my last 4 cars I will say these things do work.
My one car with 2.59's could not spin the tires with stock pulleys. After pulleys, yes it could. I doubt that 5 lb ft of tq could do that.
I have had no adverse effects of alt. output with pulleys. That is with a fairly decent stereo system (amp) setup. When you go with the 3 pulley system you get a smaller alt. pulley to keep the alt. speed up.
Also I have had no A/C problems not being able to keep up.
This is one mod I definately recommend for under 200 bux.
As far as your problem with the voltage dropping with A/C running I would say you have a problem with you alt. under load.
My one car with 2.59's could not spin the tires with stock pulleys. After pulleys, yes it could. I doubt that 5 lb ft of tq could do that.
I have had no adverse effects of alt. output with pulleys. That is with a fairly decent stereo system (amp) setup. When you go with the 3 pulley system you get a smaller alt. pulley to keep the alt. speed up.
Also I have had no A/C problems not being able to keep up.
This is one mod I definately recommend for under 200 bux.
As far as your problem with the voltage dropping with A/C running I would say you have a problem with you alt. under load.
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
I have the small crank pulley only and I had the same problem.
Yes,when the fan(s) starts the engine was a bit shaked and the ac output down, then it was very near to stall.
I raised the (in the chip) the idle 50 rpm more. (no more problem).
Now that I have a 383 with 219 cam i raised the idle to about 800 and with this higher idle the problem is inexistant.
-Beppe-
Yes,when the fan(s) starts the engine was a bit shaked and the ac output down, then it was very near to stall.
I raised the (in the chip) the idle 50 rpm more. (no more problem).
Now that I have a 383 with 219 cam i raised the idle to about 800 and with this higher idle the problem is inexistant.
-Beppe-
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
Originally Posted by amswak
how can I tell if the last owner got the three pulley set or the single pulley?
-beppe-
Race Director
Joined: Dec 2002
Posts: 13,348
Likes: 233
From: SCMR Rat Pack'r Charter Member..Great Bend KS
Alt, waterpump, and compressor speeds are carefully calculated by the factory for a street-driven Vette. Mess with the ratios and you are going to have 'issues'. Are the issues worth the slight straight-line performance gain? Only you can answer that.
Larry
code5coupe
Larry
code5coupe
Last edited by rocco16; Jul 15, 2005 at 10:13 AM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
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
Thread Starter
Instructor
Joined: Jun 2002
Posts: 218
Likes: 0
From: Winnetka CA
Haha, with an aftermarket crate motor, no cats or egr, cutom chip, and redone tranny, and many other mods, my car doesnt quite fit under factory street driven specs...not only that but I have plenty of "issues" as is because of how much has been changed...
Anyways, where would you all buy pulleys from? I am just going to call up wherever and ask what diameters their aftermarket ones are...they should know what they stock sizes are too.
Anyways, where would you all buy pulleys from? I am just going to call up wherever and ask what diameters their aftermarket ones are...they should know what they stock sizes are too.
Last edited by amswak; Jul 15, 2005 at 11:03 AM.
Pro
Joined: Feb 2005
Posts: 658
Likes: 1
From: Centerville OH
Originally Posted by amswak
Do underdrive pulleys significantly lower alternator and AC output? Also, how much power gain do they provide?
I ask because my voltage output is pretty low, and even lower with the AC running. It is so bad that if I drive around town all day with the AC on, the battery will not charge enough to be able to start the car back up. The alternator is brand new and the battery has been tested, so the only thing I can figure is that the alternator can't keep up with the power drain from the AC blower, but I dont know...
I ask because my voltage output is pretty low, and even lower with the AC running. It is so bad that if I drive around town all day with the AC on, the battery will not charge enough to be able to start the car back up. The alternator is brand new and the battery has been tested, so the only thing I can figure is that the alternator can't keep up with the power drain from the AC blower, but I dont know...
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Though I bought the March steel 3-piece pulley set I only installed the underdrive crank and overdrive alt pulleys.
I did not see any difference in time slips though the engine seems to rev quicker in 1st gear.
I believe more benefit could be obtained with the Al pulley set, which is available for '87 L98s. In fact replacing all the steel pulleys with Al would likely help a lot in 1st gear where pulley inertia could be reduced.
I did not see any difference in time slips though the engine seems to rev quicker in 1st gear.
I believe more benefit could be obtained with the Al pulley set, which is available for '87 L98s. In fact replacing all the steel pulleys with Al would likely help a lot in 1st gear where pulley inertia could be reduced.
Burning Brakes
Joined: Jan 2002
Posts: 1,228
Likes: 1
From: Dallas Texas
Originally Posted by 65Z01
In fact replacing all the steel pulleys with Al would likely help a lot in 1st gear where pulley inertia could be reduced.
Racer
Joined: Feb 2004
Posts: 445
Likes: 1
From: Atlanta GA
I went with the March Power and Amp series 3 piece aluminum pulley set (with the underdrive crank pulley and the overdrive alternator pulley). As 65Z01 said earlier, my '89 seems to rev a bit quicker in 1st gear now.
I have a custom sound system in my car with external amp, crossover, capacitor, sub, etc. and still haven't had any troubles with the charging system since I installed the pullies.
I have a custom sound system in my car with external amp, crossover, capacitor, sub, etc. and still haven't had any troubles with the charging system since I installed the pullies.
Pro
Joined: Nov 2004
Posts: 641
Likes: 3
From: Long Island NY
Originally Posted by rocco16
Alt, waterpump, and compressor speeds are carefully calculated by the factory for a street-driven Vette. Mess with the ratios and you are going to have 'issues'. Are the issues worth the slight straight-line performance gain? Only you can answer that.
Larry
code5coupe
Larry
code5coupe
Le Mans Master
Joined: Apr 2000
Posts: 6,341
Likes: 1
From: Shelton CT
Originally Posted by rocco16
Alt, waterpump, and compressor speeds are carefully calculated by the factory for a street-driven Vette. Mess with the ratios and you are going to have 'issues'. Are the issues worth the slight straight-line performance gain? Only you can answer that.
Larry
code5coupe
Larry
code5coupe
My voltage gage is showing 11.5v at idle with the ac blowing cold, 11.7-11.9 without the ac at idle, and over 14 while cruising..They defenately reduce voltages a bit..
Race Director
Joined: Sep 1999
Posts: 10,008
Likes: 0
From: cincinnati ohio
CI 5-6-7-8-9-10 Veteran
Did you need to get a different serp belt when this mod is done? The guy at March told me I would need to measure with string for the new length of the belt. Thanks.
Safety Car
Joined: Jun 2000
Posts: 4,870
Likes: 25
From: Long Island, NY
Originally Posted by MrNuke
My voltage gage is showing 11.5v at idle with the ac blowing cold, 11.7-11.9 without the ac at idle, and over 14 while cruising..They defenately reduce voltages a bit..
But, there is definetly a lower voltage output at IDLE.
During highway cruising, I get a full 14.0 - 14.4 volts.
Vic
