Power Steering Underdrive Pulley ?

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90lxwhite

I'm kind of a She-Man
5 Year Member
Aug 25, 2011
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Ma

Maybe it's negligible but so is the cost so its worth it either way. Theres literally sh*t tons of mods we all do or have done that are negligible. CAI (in my opinion a negative gain), a degree of timing, air silencer, smog pump, egr delete, ac delete, shorty headers, larger injectors, this list is endless. These mods barely do anything but are still discussed and done. So im trying something new because someone has to, or should we just keep talking about explorer intakes??
Gt40, 3.73, triax- the only words required to create a 79-95 mustang forum.
 

mikestang63

SN Certified Technician
Aug 27, 2012
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95 slides right in the 130 does not
Not true. small case 3g and 6g's slide right in and the larger case only need a minor mod on the bracket. You don't need air tools- a dremel, grinder, hacksaw, or drill with a carbide grinding bit will do the job. Well worth the 5 minutes of trimming for a much better unit and larger charging capability.

Hoping you at least upgraded and did not reuse the stock power wires.
 

90lxwhite

I'm kind of a She-Man
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Aug 25, 2011
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Hoping you at least upgraded and did not reuse the stock power wires.
hmm lemme see... T'was a couple years ago but if memory serves( and sometimes it doesn't) I think I just bolted er on in "as is." The 95 amp works pretty well so I'm gonna let er ride for now until eBay releases an alternator promising 20 horse and 30 ft lb of torque.
 

MFE92

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Aug 25, 2010
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Regarding pulley size: The problem is, the way the system works, there's not a direct linear relationship between pulley speed and pump output. Once it reaches a certain threshold, that's what it puts out. Slowing the pulley down only raises the threshold speed. The way to tune steering feel is with the rack, specifically the spool valve and the torsion bar, which determine how much assist is given to the steering, and at what steering input force.

edit: Words from an engineer who used to work for one of Ford's hydraulics suppliers:
the pulley diameter doesn't make a difference. Does you steering feel different in 2nd gear vs. 3rd gear? The pump is a fixed displacement pump (say, 2.0 gallons per minute) regardless of input speed. Well, to be more accurate, at idle you aren't making the full displacement, but soon after idle (around 1000-1500RPM) you reach full displacement and the pump goes into flow control. After that it's fixed. Adding a bigger pulley means that it takes a few more revs to go into flow control, but lessens the parasitic losses at the high end. Switching to a lower flow pump makes efforts go up, but also makes the rack speed at which you can overcome boost lower (the fluid can't fill the rack fast enough and it "catches"). Not so good.
 

Dave2000GT

Active Member
Oct 3, 2005
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Regarding pulley size: The problem is, the way the system works, there's not a direct linear relationship between pulley speed and pump output. Once it reaches a certain threshold, that's what it puts out. Slowing the pulley down only raises the threshold speed. The way to tune steering feel is with the rack, specifically the spool valve and the torsion bar, which determine how much assist is given to the steering, and at what steering input force.

edit: Words from an engineer who used to work for one of Ford's hydraulics suppliers:
"Lessens parasitic losses at high end" Thank you, this should be obvious, and you dont need a dyno to figure this out like some have suggested.
 

MFE92

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Aug 25, 2010
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Well, without a dyno or consistent drag strip testing there's no way to know if the reduction is significant. ;)
 

revhead347

Just rub Vaseline all over
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Jun 14, 2004
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Regarding pulley size: The problem is, the way the system works, there's not a direct linear relationship between pulley speed and pump output. Once it reaches a certain threshold, that's what it puts out. Slowing the pulley down only raises the threshold speed. The way to tune steering feel is with the rack, specifically the spool valve and the torsion bar, which determine how much assist is given to the steering, and at what steering input force.

edit: Words from an engineer who used to work for one of Ford's hydraulics suppliers:

Good info in there anyway. I like picking up titbits like that. Thanks for posting the quote.

Kurt
 

Shockj2000

New Member
Nov 21, 2020
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Has anyone had experience running just the PS underdrive, while leaving the crank pulley at stock ? Is there any change in power or steering response ?

It's offered by this company on ebay
http://rover.ebay.com/rover/1/711-5...0001&campid=5335821607&icep_item=221275612448

I'm thinking of giving it a try at the same time as I do an AC delete since I'll be re-sizing the belt already.
So I went ahead and threw the underdrive pulley on. I noticed even though it's bigger it's also a bit lighter which is good to reduce the weight of the pulley system. It works - I think the steering does feel a bit better, beyond that I can't tell if it made any difference. It was really easy to do with the free tool rental from autozone, took like 15. Without the tool it would be impossible and you'd break the power steering pump, that's probably why it's not a standard on pulley kits.
Hey Dave not sure you will read this because it’s such an old thread. Do you know what kind of belt you used? The parts still for sale online and he states to use a different belt but doesn’t know what belt to use
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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This member has not been around since 2016, he likely will not respond, anyway I would recommend not running an under drive power steering pulley.