Decoupler Pulleys - for the 2.8-3.4? (Page 1/2)
82-T/A [At Work] MAR 09, 11:26 AM
Hey guys... not sure if everyone here knows what this is... but does anyone know if there's such a thing as a decoupler pulley that's available for the GM alternators in our Fiero?

It's something that I installed on my Crown Victoria, and really helps the reliability of both the alternator, the belt, and the accessory system.


Here's a good video to explain how it works:




Long and short... the civilian Crown Victorias didn't come with these, but the Police versions did because of the way they're typically driven. I upgraded my Crown Victoria years ago with most of the performance parts from the police and Marauder variant. The shift from 1st to 2nd, even with 2.73:1 gears at max RPM is just insane. There's so much difference in the belt speed that the pulley squeals for a quick second, even with all brand new parts (tensioner, and everything in good shape). It's a problem Ford fixed by installing these decoupler pulleys.

Just curious if anyone knows if there's any way to retrofit one of these pulleys onto the Fiero's alternator shaft?


Thanks!!!

[This message has been edited by 82-T/A [At Work] (edited 03-09-2022).]

82-T/A [At Work] MAR 09, 11:36 AM
Here is a really good video that shows the difference between using a solid versus an OAP at high speeds...

Aside from the obvious craziness with the belt... the big take-away is that the alternator is not really creating the lag on the motor that it would otherwise be doing at full throttle... so if I understand correctly... you're actually not getting that parasitic loss at WOT over a certain RPM.
ericjon262 MAR 09, 02:18 PM
I'm fairly certain most late model GM alternators use a pulley like this, I also think the make one in the same form factor as the alternator in my swap, I may try one out. to answer your question, I think the best way to find out is to take a ton of measurements off of the alternator you want to install the pulley on, send them to a manufacturer, and see what they say.

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"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."

cognita semper

theogre MAR 09, 08:17 PM
These are Not to "Save Power" for Engines at WOT or at any lower RPM.
If anything will Create some Lag for the Alt...

Because Is to protect the Belt from the Alt's Rotor Mass. When you Hear Belt Squealing then the belt is "dead." These pulleys prevent belt death way before you hear noise.

Alt Rotor is Heavy and Slams the belt when Engine RPM changes suddenly.
Don't think so? Put an alt bolted down to a bench and try to spin to just 2000-3000 RPM then try to stop fast. Alt can spin a lot more then that. Many have "Red line" at 9000 to 10,000+ Alternator RPM.

Worse, Many newer cars and Police versions have "Heavy Duty" alts like CS144 and related w/ rotors that are heavier than CS130 or 12SI.

Pulley w/ 1 way clutch only stops slamming for high to low Engine RPM.
Advance Pulley w/ extra load spring can stop slamming in high to low and low to high.

Can you install them to replace solid pulleys?
Maybe.
Some move the pulley out and won't fit w/ OE Alt brackets to keep belt alignment.
Some are bigger front to back and may cause clearance problems w/ Fiero frame.
If you use the "wrong" advance pulley, even if it fits the belt setup, the "load spring" can made the alt to slip way more or never slip and either can cause problems.

Think the "Load Spring" as a non-adjustable Torque Wrench w/ a clutch instead of "click" bar.
If set light then will slip more and wear out fast and may cause low power too.
If set tight then will rarely or never slip and doesn't protect the belt.

Advance Pulley setup is likely affect or changes for Idler pulley setup. IOW They work together for long belt life.

Before you claim AC does the same... No. ECM/PCM can turn off AC at WOT or over some % Throttle for Decades and can be programed to turn off for other reasons.
Fiero ECM can do this too but many Throttle Pedal and Cables have problems and TB/TBI never reaches WOT. Many can't reach 80-90% Throttle when you "Floor the gas" because of this.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 03-09-2022).]

82-T/A [At Work] MAR 11, 11:01 AM

quote
Originally posted by theogre:

These are Not to "Save Power" for Engines at WOT or at any lower RPM.
If anything will Create some Lag for the Alt...

Because Is to protect the Belt from the Alt's Rotor Mass. When you Hear Belt Squealing then the belt is "dead." These pulleys prevent belt death way before you hear noise.

Alt Rotor is Heavy and Slams the belt when Engine RPM changes suddenly.
Don't think so? Put an alt bolted down to a bench and try to spin to just 2000-3000 RPM then try to stop fast. Alt can spin a lot more then that. Many have "Red line" at 9000 to 10,000+ Alternator RPM.

Worse, Many newer cars and Police versions have "Heavy Duty" alts like CS144 and related w/ rotors that are heavier than CS130 or 12SI.

Pulley w/ 1 way clutch only stops slamming for high to low Engine RPM.
Advance Pulley w/ extra load spring can stop slamming in high to low and low to high.

Can you install them to replace solid pulleys?
Maybe.
Some move the pulley out and won't fit w/ OE Alt brackets to keep belt alignment.
Some are bigger front to back and may cause clearance problems w/ Fiero frame.
If you use the "wrong" advance pulley, even if it fits the belt setup, the "load spring" can made the alt to slip way more or never slip and either can cause problems.

Think the "Load Spring" as a non-adjustable Torque Wrench w/ a clutch instead of "click" bar.
If set light then will slip more and wear out fast and may cause low power too.
If set tight then will rarely or never slip and doesn't protect the belt.

Advance Pulley setup is likely affect or changes for Idler pulley setup. IOW They work together for long belt life.

Before you claim AC does the same... No. ECM/PCM can turn off AC at WOT or over some % Throttle for Decades and can be programed to turn off for other reasons.
Fiero ECM can do this too but many Throttle Pedal and Cables have problems and TB/TBI never reaches WOT. Many can't reach 80-90% Throttle when you "Floor the gas" because of this.




I'm primarily looking for the "override" pulley. I have to assume that the shaft on the alternator is not something so unique that an existing pulley wouldn't fit. I think spacing is a problem I could easily fix, and the number of splines on our serpentine belt is fairly common.

I just can't imagine why others have considered this, or implemented it. It's only a net-positive as it reduces load on pretty much every accessory, including the bearings and brackets. It reduces load to the engine on acceleration, and on deceleration.

Are there any instances of a modern-V6/60 (gen 3 maybe) with this being used? Anyone know?

Thanks Ogre...
pmbrunelle MAR 11, 12:57 PM
During acceleration, the overrunning pulley locks and becomes solid... so how would that reduce loads on everything during acceleration?
82-T/A [At Work] MAR 11, 01:57 PM

quote
Originally posted by pmbrunelle:

During acceleration, the overrunning pulley locks and becomes solid... so how would that reduce loads on everything during acceleration?




Hmm... I guess I thought it did. I assume that's the same for both of them then?
theogre MAR 11, 09:06 PM
Babcox authors of many "trade rags" have video in Underhood Service channel w/ cutaway of both types...
https://www.youtube.com/watch?v=DJBMkfI9CYc


quote
Originally posted by pmbrunelle:
During acceleration, the overrunning pulley locks and becomes solid... so how would that reduce loads on everything during acceleration?

Mostly Correct.
the 1 way unit will "lock" in accel and cruise then "Free wheel" when decel, more so when engine RPM drops fast.
The "advance" pulley will "lock" most of the time but "Free wheel" when engine RPM changes fast in either direction. Or May "Eat" any shock from the alt to engine and the opposite. This version can be tuned for a given vehicle.

If OEMs setup the idler tension less that normal then belt strain on Alt & other bearings helps them too.
Otherwise bearing loads don't change very much.

Brackets and other hardware won't change because of other loads and vibration are same.


quote
Originally posted by 82-T/A [At Work]:
I just can't imagine why others have considered this, or implemented it. It's only a net-positive as it reduces load on pretty much every accessory, including the bearings and brackets. It reduces load to the engine on acceleration, and on deceleration.

Again. Assume you find either type w/ same diam and spacing as the solid pulley...
Is often not a direct replacement.
Alt Shaft maybe different or have clearance problems stated above.

Even If that doesn't happen, need special tools to install/remove them. Example: https://www.youtube.com/watch?v=XYi_w3ieGUo
Likely isn't cheap when buying a pulley either. not something to find in most junk yards and Gates etc. are tell to change them every time you change the belt.
Dennis LaGrua MAR 12, 07:22 AM
Quite frankly I don't like them. Modifying adds another element that could go wrong. I don't see any advantage on a classic hobby car that gets used little.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Blacktree MAR 12, 10:43 PM
IIRC the 3800 has an overrun pulley on the alternator. I think some other GM engines do, as well. Maybe you can adapt one of them? But to be honest, I don't see the point.