UnderDrive Pulley's

Ended up with multiple sets of different metal UD pulleys to use on my project trucks, so figured I'd compare them. I always find it interesting to compare parts and sometimes buy different ones just for that(not that it was my intent here).

A lot of people don't need or think UD pulleys are worth it and that's fine if they think that. Some expect every mod to feel like a 100 shot of NOS tho LOL But it's a mod I like to do, since I do many other things as well. One interesting point I found, was how auto trans sometimes have issues with the UD alt pulley. Not had any volt issues with my auto cars but I do often get rid of a lot of other stuff. My project trucks are both manual so don't expect any issue with them either but March Performance does recommend diff kits, for diff trans type on these trucks.

Anyways long story short the steel are heavier than the alum, go figure LOL It's bout 1lb diff for the crank pulley and 1/2ish for the alt

Not thrilled about turning the water pump and fan, and A/C compressor slower, on a pickup.

A high-rpm "race" engine could be a different story.

BOOT said:

One interesting point I found, was how auto trans sometimes have issues with the UD alt pulley.

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I would love to hear more about *that* story.

On first blush I would have to assume that the UD pulley resulted in low-voltage condition at or near idle, which in turn caused a downstream effect(s), e.g., in the auto trans as you mentioned.

But I could be all wrong.

1998_K1500_Sub said:

I would love to hear more about *that* story.

On first blush I would have to assume that the UD pulley resulted in low-voltage condition at or near idle, which in turn caused a downstream effect(s), e.g., in the auto trans as you mentioned.

But I could be all wrong.

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At idle in gear, so at like stoplights n such

Underdrive pulley, how do define under drive? Are using a smaller diameter or larger diameter? On specific drives, ie AC , alternator, water pump, power steering? Or crank drive?

Schurkey said:

Not thrilled about turning the water pump and fan, and A/C compressor slower, on a pickup.

A high-rpm "race" engine could be a different story.

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I underdrive my one mech fan car even more and my electric fan car bout the same and those both have smaller radiators Still as i said in my orig post I do other stuff, like for example lower thermostats. Also my stuff is project fun drivers, not really daily stuff or a work/tow truck(those I deff wouldn't).

GoToGuy said:

Underdrive pulley, how do define under drive? Are using a smaller diameter or larger diameter? On specific drives, ie AC , alternator, water pump, power steering? Or crank drive?

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Smaller drive pulley, larger driven pulleys.

UD pulleys are good for 3000+ RPM's to reduce load on the engine and so you don't spin the guts out of your accessories,not needed or desired on daily drivers. Aluminum is quite a bit lighter but also wears faster than good ol steel. I've installed a few of those Marsh drives. They're decent quality and not too big a PITA getting them aligned. One tip I can offer is apply a light film of light oil to the PS pump pulley and shaft before pressing it on or you will have a baaaad day.

BOOT said:

At idle in gear, so at like stoplights n such

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OK, so what happens to the auto trans behavior, and why is it sensitive to the alternator's low output (essentially running on battery voltage)?

Inquiring minds want to know.

Instead of UD pulleys, how about we just change the rear gear from, e.g., 3.42 to 2.73, and underdrive the entire powertrain / accessory package while at road speed at 80%, yet let it operate normally at idle?

1998_K1500_Sub said:

OK, so what happens to the auto trans behavior, and why is it sensitive to the alternator's low output (essentially running on battery voltage)?

Inquiring minds want to know.

Instead of UD pulleys, how about we just change the rear gear from, e.g., 3.42 to 2.73, and underdrive the entire powertrain / accessory package while at road speed at 80%, yet let it operate normally at idle?

Click to expand...

Doesn't effect the auto trans, because of having an auto trans, the idle is lower(in gear vs clutch in), so the alt charge is also lower and that can cause issues in general.