Does a shorter serpentine belt actually useful?

I have a Audio setup in my car, since my belt is worn and needs replacing someone recommended me to go with a shorter belt to help with the dimming and to help with power. (at idle or car stopped etc)

However, another person told me the tensioner is set for a certain spec and would likely just be the same.

Has anyone heard of this? Curious before I stress myself out with a belt that’s already a biscuit biting bulldog to get on lol.

They told you right replace both the belt and tensioner.


I have no idea what that ‘someone’ is talking about. Go with the correct specification belt and idler.


Agree better that way than a break down at the wrong place and time.

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I think it best in the long run to stick with the stock sized belt, correct tensioner, and get an alternator that can actually keep up with the additional load.


The mechman high output alternator was half inch off from the mount hole, And wouldn’t force drill on. I ended up returning it, found another brand and that burnt in about 5-6 months. So I figured it was junk. Now im in a Delma that the serp belt or tensioner is the culprit for all these bad alternators.

So that’s why I posted if I should go shorter since I’m gonna remove it anyways.

Hopefully “next next” highoutput alternator work 3rd times a charm

Hi Blankensnake:
Do you have both:

  1. The specs for how much power your audio system draws,
  2. The power output specs (amperage) for the high output alternator that burned out on you?

I know caddy limos had a dual alternator setup. I assume most engines could do that. Remove the ac compressor. Put in a 2nd alternator.

Subwoofer CompR Dual 12’ Kickers: Recommended Amplifier Power (watts RMS) 1000
Peak Power (watts, per ANSI/CTA-2031-A) 2000

Amp: Comp R kicker amp * mono subwoofer amplifier

  • 900 watts RMS x 1 at 4 ohms (1800 watts RMS x 1 at 2 ohms)
  • 1800 watts RMS +/-10% x 1 at 1 ohm

1# OEM 80A
2# AutoZone Rebuilt 80A
3# mechman 250A highoutput (didn’t fit)
4# Ebay alt 250A (said it burnt out to slipping belt during boost when I returned it)
5# TYC rockauto alt 80A
6# lifetime warranty ^ (and currently in part 2 lol)

car runs oil press, boost , and wideband gauges, after market radio, turbo timer and always have police radar in cigeratte lighter for other electronics I can think of

That says it all right there.

Definitely not enough power.

I want to know where you got the police radar and how often does it need to be calibrated?


Hi Blakensnake:
Your car came with an 80A alternator.
Your stereo at 1000 watts will draw 83A, (and that’s excluding peak audio amp usage), and that’s not including supplying all the power your vehicle needs to run and all your added electronics.

When I read your post, my reaction is:

  • You need at least a 250A alternator (to handle going over 1000 watts).
  • Any 80A alternator you use will burn out, rather quickly.
  • The Ebay 250A alternator will have questionable quality. It may be reliable, but how will you know? And if it didn’t fit correctly, you need to find one that does.

Based on the updated information that you provided, it sounds like your original post is asking if you can use a Ebay 250A alternator and “make it work correctly” by installing a shorter belt.

Please confirm.

I and many others here have installed shorter belts on vehicles over the years, especially when custom work was being done. It will be nearly impossible for us to be able to tell you if you can successfully do it in your set-up.

appreciate the electronic conversion something I lack in,

Ebay alt was last resort yolo when I was 19 and we were all doing dumb stuff to our cars lol. (Once we shaved off the top of a car to make it a convertible $200 auction junker lol we dont know why.) Anyways I bought it because the actual branded one didn’t fit. I also intentional tried burning and destroying it to get 90 day money back as I knew quality was definitely not gonna be there.

To many people are saying it isn’t worth a different belt. So now my main question is (since now this will be a normal belt + tensioner + highoutput once again fingers crossed) Do I need to do any of the following?

Do 0 guage upgrade (4 right now)

Or do I put a spare battery in my trunk, drill my fire wall and run an additional cable on the alt and run it to the back

Or should 250A be plenty and possibly my belts been worn for awhile? Just trying to avoid issues once I put everything in so I don’t have to be repeating this in 6 months.

The power output of the alternator directly corresponds to its rpm, and a shorter belt won’t change the rpm. A smaller alternator pulley would increase the spin rpm and its potential output power tho, maybe they mean to change to a smaller pulley, which might require a shorter belt. Other than that, suggest to stay with the original belt length and original tensioner spec. Otherwise could damage all the bearings in the belt path, or cause belt to slip.

You may be up against fundamental limits. The engine configuration is only able to produce so much electrical power, beyond that requires major ($$$$) engine compartment changes. .


I’ve made bad decisions as a young adult. George I wish I knew you before I got everything and put myself in this situation. Because yep big headache to add extras and $$$ luckily lifetime warranty and one year warranty’s saved my butt in almost every occasion besides OEM one.

Star Trek motto: “Go where no man has gone before” … the problem with that theory applied to your case is that the Federation was paying the bill … lol …

Hi Blakensnake:
I was under the (perhaps mistaken?) assumption that your asking about the shorter belt was just to address the belt slipping issue you had with the “Ebay 250A alternator” that didn’t fit correctly. And that the “incorrect fit” could be addressed with a shorter belt.

If that’s wrong, please let me know.

I would not seek any change in belt length if you’re trying to change the pulley size, nor would I change the pulley size to spin the alternator faster. Nothing good will come out of that.

You shouldn’t need a spare battery in the trunk if your alternator can meet your electrical system’s load.


You say an audio system. Does that mean the trunk is full of power sucking amps or what?

Keep in mind that a 250 amp alternator is not going to put out 250 amps (maybe and very briefly) before it goes up in flames.

Another unknown is exactly how all of this is wired up. Amps wired through a lighting circuit or what?

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I replaced my alternator a few months ago with an OEM Delco, same as it had in it. Seems to me it was 125 amps, so 80 is very light duty to be putting that extra load on.

Is there a properly overload protected 80 Amp alternator that you can get? At least it wouldn’t burn out. EBay is full of falsely advertised products, so I doubt it was actually 250A.

If the belt is slipping on the alternator wouldn’t that cause a squeeling sound to be heard? They said the belt was slipping when he returned it but it could be that it was an 80A alternator that was faked to 250A.

Electric motors, like for vacuum cleaners, sometimes protected with a thermal-trip fuse. Prevents winding insulation from melting. I don’t think that sort of protection is common in automobile alternators, although including that function seems a good idea. Slipping belt may or may not squeal.