Can you over-rev the PS pump or alternator? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 12-31-2002, 07:03 PM
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Can you over-rev the PS pump or alternator?

I am converting my 5.0 to v-belt instead of the serpentine belt, and the drive pulley I have has three groves. The outter two are bigger than the inside one. The inside grove is the same size as my stock CJ drive pulley (258) was, and I am using the CJ ps pump, and alternator. I don't want to have to use one giant v-belt to run the water pump, ps pump and alternator, but the other groves on the drive pulley are going to turn the alternator or ps pump faster than stock. Is this bad? Which would be the one to spin faster if I had to? BTW, the bigger drive pulley(s) are about 1 inch or so bigger total diameter. Thanks!

Mike
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post #2 of (permalink) Old 12-31-2002, 07:56 PM
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Re: Can you over-rev the PS pump or alternator?

1. Pulley size is proportional to pressure.
2. Revs is directly proportional to pressure.
3. The pump has a relief vavle if overpressurized.

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post #3 of (permalink) Old 12-31-2002, 08:11 PM
 
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Re: Can you over-rev the PS pump or alternator?

Most automotive alternators have a pretty predictable output curve. At 1,000 RPM or less output current is generally less than 25% of the stated rating. At 3,000 RPM output is in the neighborhood of 80 to 90% of the stated rating. Maximum rated output is generally specified at 6000 RPM. Flyapart speed is probably in the area of 10,000 RPM. I run mine at about 2.5 times engine speed but I rarely go above 3,500 RPM in my Jeep.

Power steering pumps present a different problem. Pump output volume increases with RPM ... To a point. When the pump reaches its critical point it begins to cavitate and output volume drops drastically. I don't have any power steering pump data but I'll get some.
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post #4 of (permalink) Old 12-31-2002, 08:40 PM
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Re: Can you over-rev the PS pump or alternator?

If the larger drive pulley does cause an issue, maybe you can find larger driven pulleys to even it back out? They are widely available via aftermarket as "underdrive" pulleys. Most "hotrod" rags will have several advertised.
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post #5 of (permalink) Old 12-31-2002, 09:02 PM
 
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Re: Can you over-rev the PS pump or alternator?

I did some quick reesearch on power steering pumps and most have a max speed rating of between 6,000 and 7,500 RPM. Of course no one will say whether that number is the cavitation speed or the physical limitation of the pump.

I would design for a maximum 6,000 RPM pump speed.

For sh!ts and giggles, why don't you figure out what ratios you have with the serpentine setup. That will give you ball park numbers to start with. Later on you can swap pulleys to tweak your application.
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post #6 of (permalink) Old 12-31-2002, 09:36 PM
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Re: Can you over-rev the PS pump or alternator?

Man, you guys are Awesome! Thanks a ton! Diagrams, even... [img]images/graemlins/laugh.gif[/img]

Hey Dave, do you still want the T5 tranny? The holidays were crazy busy and I forgot all about it [img]images/graemlins/frown.gif[/img]

Mike
post #7 of (permalink) Old 12-31-2002, 10:27 PM
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Re: Can you over-rev the PS pump or alternator?

Hey Mike, I think my brother would still like to have it. Get *your* Jeep running first! His is still moving........for now [img]images/graemlins/grin.gif[/img]. Besides, he's got some new bling-bling junk to bolt on first [img]images/graemlins/smirk.gif[/img]. When you get a breather, let me know about shipping.
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