Let's test alternator belt tension/mpg!
 

I recently tightened my alt belt as it'd stretched since installing it. It was squealing at start up. I am wondering whether the increased tension=worse fe.
Anyone with instrumentation have interest in testing to see whether tension plays a significant part.

If so, I am thinking if we all loosen our belts to where they are tight enough so as not to squeal, maybe we will get slightly better fe. ;)

I would think that a newer/less glazed over belt would be better as it wouldn't need to be as tight to still grip the pullies, mostly "V" belts are a bad high friction design, ribbed belts seem to be a bit better, and cog belts are are really nice, but more costly.
I find it interesting that in reading about the Civic FE, it's suposed to have slightly less belt tention on the alternater belt then the normal 1.3 or 1.5L civics did, altho they don't give a good reason as to what's different.

I'm actually undergoing this same thing with my car: there is a belt under the hood that squeals occasionally from startup. I'm pretty sure that a loose belt if bad for FE because whenever the belt in my car squeals, my acceleration is dimininished/held back. Therefore the longer it takes me to accelerate, the longer the Scanguage shows 15-25mpg before attaining my cruising speed.

My belt is ribbed. You say cog belts are better, but can I use one on my alternator, or would i need toothed cogs to run it like my timing setup?

a cog belt needs toothed cogs, if you had a lathe, you could adapt some to work, but both the sprockets and belts cost more, but "V" belts are something like 85-92% efficent, cog belts are something like 95-98% efficent, and bicycle chain up to 98%... but at high speeds if you get a bit of gravle in a chain... bad things can happen, belts are soft and you can find bits of rock imbedded in old belts.

When I bought my Metro/Swift it had an old ribbed belt that squeeled sometimes.
So i replaced it with a new belt , now it squeels all of the time even tho I have retensioned it 3 times (pain in the %&/ job) :thumbdown:

I have never had a slippage problem with V belts.

Agreed.. probably some bearing is about to blow its guts out.

Low belt tension can result in slippage on the alternator and low battery voltage which can affect spark and fuel injection. I run a Gates belt on my scooter and can measure the extra load when too tight and running loose on a toothed belt is not a problem but too loose can cause it to walk off the wheel sprocket. It doesn't make that much of a difference - an amp or two at 38 volts under no load conditions.

I wouldn't be suprized if v-belt manufacturers would disagree with my figures, but it's not hard to disagree, I admit that I only did a quick google search to varify that I wasn't way off on the numbers that I had in the back of my head from reading an artical on drive train designs for human powered vehicles, and the pages I turned up seemed to agree with my numbers, but the main point is that v-belts are not an efficent way to transfer energy.

I've experienced this in my car too.

Mostly because I was taking my belt off and putting it on so frequently when the weather was nice, and sometimes I didn't get it tight enough. I have a wing nut for alternator tension :)

If your alternator belt slips, the alternator will slow. To compensate for the reduced output from lower RPM, the voltage reg will feed more current into the field to make a stronger electromagnet (to generate more power at lower RPM). So the alternator is now significantly harder to turn, and the belt slips even more, and it becomes a vicious circle.


I'd say a loose belt is definitely bad for MPG - the way our alternators respond, anyway.