Alternator RPM

Jerryl

Tall Chinese Guy
Dec 14, 2004
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Houston, Texas
Does anyone know the max sustained RPM of the stock alternator?

I have not measured and calculated the alternator RPM with stock pulleys, and wondering if anyone has, and is willing to share.
 

No disintegrations

Active Member
Dec 27, 2015
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The quick version of what I've read on this. Minimum output speed at alt shaft Near 2400 rpm
Max electrical output near 6000 rpm and never exceed 18,000 rpm.
We have a snowmobile with an automobile style alt and that engine sees 8200 rpm throughout the days ride. People have measured those pullies and came up with darn close to 18,000 alt rpms.
 

Nick Micale

Tech Advisor
Staff member
May 26, 2001
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www.ArizonaGN.com
I have had issues with after market alts at 6-7000 RPM as the output drops to 12.0 or so.

After replacing the pulley with a stock one which gave better output, but still output drops over 6000 RPM.

After discussing this with an alt repair shop, I was informed these alts has a built-in limiter which drops off voltage at high RPM.

I use a volt booster which gives 14 volts at RPM, but I now use an aftermarket alt with a stock pulley and a life time warranty, as the alt last will only last a year or 2!
 

3.8L V-8 eater

Well-Known Member
Jul 22, 2006
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I have had issues with after market alts at 6-7000 RPM as the output drops to 12.0 or so.

After replacing the pulley with a stock one which gave better output, but still output drops over 6000 RPM.

After discussing this with an alt repair shop, I was informed these alts has a built-in limiter which drops off voltage at high RPM.

I use a volt booster which gives 14 volts at RPM, but I now use an aftermarket alt with a stock pulley and a life time warranty, as the alt last will only last a year or 2!
I just had to pull my car off of the dyno 2 straight days...Fuel pressure was dropping and after the first day put in a new pump and went back, but was still getting fuel pressure drop...Turned out my voltage was dropping down into the 12's under heavy throttle...I assume the alternator is no longer keeping up....Nick have you ever seen it a wiring issue when voltage was dropping??
 

dank GN

BlackArts Automotive (661)993-8277
Jan 11, 2009
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SoCal the high desert
Like Nick said I’m running a 140amp alt from autozone for a caprice. If i have had 1 issues with it the best part is all I have to do is take it and swap it to a new one . But I have yet to have a issue with it . Btw I’m running a smaller crank pulley so I installed a larger alt pulley to keep the alternator in its stock rpm configuration.
85F29668-ECB9-4B98-AABA-CD6850254A83.jpeg
 

Jerryl

Tall Chinese Guy
Dec 14, 2004
8,315
1,036
113
Houston, Texas
Thanks guys.
I do not have a charging problem and did estimate a 3:1 stock ratio.
Just thought there would be some value in a slightly higher ratio.

A quick calculation indicates that a 3.1:1 ratio should provide better lower RPM performance while staying below the max alternator rpm for 90% of our cars.