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-   -   Performance Underdrive Pulleys? (https://www.fuelly.com/forums/f10/performance-underdrive-pulleys-5979.html)

cfg83 09-04-2007 10:08 PM

Performance Underdrive Pulleys?
 
2 Attachment(s)
Hello -

What do you think of this? :

Underdrive Pulley
https://www.saturnmotorsports.com/cat...roducts_id=224
Attachment 904
Quote:

By reducing the engines rotating mass while underdriving your accessories, these lightweight T-6 billet aluminum underdrive pulleys will deliver an increase in horse power. This kit replaces your factory crank, alternator and water pump pulley. The Saturn underdrive pulleys are perfect for naturally aspirated, Turbo, and Nitrous applications.
I was *trying* to find a special custom pulley that was made in Canada by a dude that seems to have disappeared, but now I found this "performance pulley set".

Do you think it would increase MPG?

CarloSW2

Danronian 09-05-2007 09:11 AM

If your saturn motor has a dampener combined with the stock pulley, don´t use the underdrive unit or you could see some crank bearing damage in the future.

But other than that, the only problem I´ve heard with using them on the alternator is that it won´t charge your battery enough. I can see how they would help a little by not spinning the accessories as much, but they would still be connected, so I doubt the advantage would be that huge.

VetteOwner 09-05-2007 02:04 PM

well, i noticed a crapload of more tourque on my truck. i just changed out the big steel crank pulley with a smaller aluminum one. i also changed the alternater pulley to as smaller one to keep it spinning the same. i changed pullies and took out my egr valve at the same time so i cant really say which did what but all of a sudden i got 2-3 mpg better. and liek i said it noticeably freed up some tourque and where theres more tourque means theres less gas involved to accelerate the same.

GasSavers_Ryland 09-05-2007 08:08 PM

the light weight would be and advantage, but the under driving your alternator could cause problems at idle.

VetteOwner 09-06-2007 04:43 PM

no you make the alternater pulley smaller along with the smaller crank pulley, keeping the ratio between the 2 the same, which keeps them spinning at the same speed. the volt meter on my truck hovers right at 14, which is where it was before the swap.

mrmad 09-06-2007 06:17 PM

Quote:

Originally Posted by VetteOwner (Post 71148)
no you make the alternater pulley smaller along with the smaller crank pulley, keeping the ratio between the 2 the same, which keeps them spinning at the same speed. the volt meter on my truck hovers right at 14, which is where it was before the swap.

Not sure about Saturns, but for Hondas, these are underdrive pulleys. You can either get the crank pulley that has a smaller dia, or separate alternator and PS pulleys that are larger for the same effect. My Integra has AEM underdrive pulleys on the alternaots and the PS pump. I don't notice any issues withthe PS, at idle, the voltmeter does drop down to 12V, but at about 1200 rpm jumps up to the 13.4 it normally sits at. I guess if I idled it for a real long time, I could drain the battery, but it never has.

GasSavers_Ryland 09-06-2007 07:03 PM

one big disadvantage of useing smaller pullies one both ends of the belt to keep the ratio the same is that the stiffness of the belt trying to curve around that smaller pully is harder on the belt, is going to increase the chances of the belt sliping, and to over come that slipage of the belt is going to need more tension on the belt, leading to increased bearing wear and belt wear, in an ideal world you would simply have lighter weight pullies that were the same size, or even larger, I would love to use a cog belt insted of a ribbed belt as it needs even less tension because of it's gear like teeth, and maybe simply use plastic gear pullies to save weight.

markweatherill 09-06-2007 10:44 PM

Plastic gear pulleys, I'd buy *that* for a dollar!

I wonder why nobody is making those. Perhaps it's wear rates or balancing issues.

cfg83 09-07-2007 12:01 AM

2 Attachment(s)
Ryland -

Quote:

Originally Posted by Ryland (Post 71166)
one big disadvantage of useing smaller pullies one both ends of the belt to keep the ratio the same is that the stiffness of the belt trying to curve around that smaller pully is harder on the belt, is going to increase the chances of the belt sliping, and to over come that slipage of the belt is going to need more tension on the belt, leading to increased bearing wear and belt wear, in an ideal world you would simply have lighter weight pullies that were the same size, or even larger, I would love to use a cog belt insted of a ribbed belt as it needs even less tension because of it's gear like teeth, and maybe simply use plastic gear pullies to save weight.

I think this is designed to solve the slippage problem :

3 Way Adjustable Billet Idler Bracket
https://www.saturnmotorsports.com/cat...roducts_id=799
Attachment 910
Quote:

3 way adjustable billet idler bracket eliminates belt from slipping with smaller pulley upgrades. Very easy to installation.
That's *another* $99 on top of the $250 for the pulleys, :thumbdown: :mad: .

CarloSW2

cfg83 09-07-2007 01:22 AM

2 Attachment(s)
theclencher -

Quote:

Originally Posted by theclencher (Post 71198)
I'm pretty sure Ryland's point is with the smaller pulley's ya gots'ta bend the belt more, and bending the belt more take's more energy,,,,,,,,,,,,,,,,,,,,, thu's it's LESS efficient,,,,,,,,, compound that with more tension to keep slip under control,,,,,,,,,,,,,,,,, another efficiency hit.

Attachment 911
ARGHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH!!!!!

CarloSW2

Snax 09-08-2007 08:04 PM

Let's just put this into more concrete terms on some arbitrary efficiency numbers:

Assuming your accessories sap about 20% of your efficiency at idle, a 10% underdrive pulley is going to improve overall idle efficiency by roughly 4%. A 20% underdrive bumps that to 8% at idle.

I think it's fair to assume that the inefficiency of running the belts through a tighter bend is relatively minor - particularly if you upsize one or more of the accessory pulleys being driven.

I think it's also important to note that the improvement I suggest is at idle only. As rpms increase, you get into the accessories like power steering pumps and alternators bypassing/reducing their load on the system. So while one may see a 10 or 20% improvement in efficiency at idle, that won't translate directly to higher rpms - unless something like a clutchless fan is being driven.

Based on that, there should be a measurable improvement, but higher rpm running will limit it.


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