Did slants ever come with 2 belt alternators or was that only a v8 thing?

Right now I have one belt going from vibration dampner to water pump to alternator, then the other goes from a pulley infront of the dampner to power steering.

Problem is, I want to run two belts on my alternator. The only way I could think of doing it is add another waterpump pulley, then run one big belt that goes from alternator to waterpump to powersteering to crank.

Why does your alternator need two belts to run it?

You can get a 2-groove water pump pulley from a slant 6 with air conditioning.

Having belt slippage issues under heavy loads....

Do the double water pump pullies from ac cars.... does it place the second pulley closer to the block or closer to the radiator? I'd need something closer to the radiator because if its closer to the block, running the belt up to the alternator will hit the head.

And, if it is closer to the radiator, then this will bring up the same issue, the pulley one step infront of the dampner leads to power steering so I'd need one ultra-long belt to stretch from powersteering clear across to the alternator.

Running one belt from alternator directly to waterpump and not the crank wouldn't do me any good because all the torque from the crankshaft is still being transmitted through one belt.

If you are getting belt slippage under heavy loads, it is because something is wrong, not because you need two belts on your alternator.

What are the exact conditions under which your belt is slipping? Which pulley is it slipping on? And what is the diameter and amperage of your alternator?

This is a powermaster GM unit. Alternator is rated at 200 (or was it 250?) @ 13.5V. I doubt I'm drawing anywhere near that though. Less then half, I'd guess. Pulley diameter on it is 1.5, maybe 2" at most. Everything else pulleywise is stock. I know its overkill but at the time I bought it I figured if I'm gonna upgrade I'm going all the way in one swoop.

I believe the factory used double belts on the v8's that had the heavier duty 75-100A alternator units but I'm not sure.

Its slipping mostly on the alternator pulley because the valve cover, coil/bracket and alternator case is coverd in fine black powder of the belt shredding. There is also a little powder on the water pump pulley.

I had a slight alignment issue going on but I fixed that and replaced the belt as well today. Before I did anything I took it to the local alternator/starter shop and he told me that the problem I'm having wasn't really due to belt alignment because I wasn't that far off, it was due to the belt slipping/wobbling vertically due to the excessive HP requirment to run the alternator. And seeing as how factory used double belts on alts. putting out far less current, I thought the guy had a valid point.

I suspect the V groove in the pulley for the alternator is not designed for the fan belt that you are currently using. Running mismatched belts and pullies will cause them to shred. You may have to change the alternator pulley to match the other pullies.

I thought it could of been a pulley issue too but the alternator guy said its fine, they are both 3/8" V groove.

The only difference I can see in the GM v-groove pulley and the fan/dampner is that at the very bottom of the GM groove, its flat, where as at the very bottom of the mopar ones its rounded. The alternator guy said V groove belts grab at the sides, if the belt sinks all the way to the bottom it will slip no matter what.

Yep, sounds like an improper belt groove and definitely a too-small alternator pulley. WAY too small.

Why such massive overkill on the alternator...?

Can you calculate what speed your alternator runs at?
If i remember correctly, Alternators typically run about 3 times the rpm of the crank or so.
I think that style alt would have plenty output at a kinda low rpm, so maybe you would want a bigger pulley.
The belts are also made for different diameter pulleys, so maybe it is just "bending" too much, trying to wrap around the small diameter?
You can try a belt fron a industrial things store instead of a autoparts store.
Ask if they have something that would work for you...

Assuming no slippage, the crank/alternator speed ratio is just the ratio of the pulley diameters. The smaller one turns faster.

I just measured with a ruler, the GM alternator pulley is roughly 2 3/8" outer diameter, and the stock one is 3". I have a spare dampner here that I measured at 7". So the stock ratio is 2.33:1 and with the gm pulley it would be 2.95.

Dan, only reason I got that alt. is because it was the highest current I could find. Powermaster website said it would be bolt in with no mods required, so I was quite happy to find a 200A drop in alternator. Later I find out its drop in for v8's only after I had it in my hands so I just decided to make brackets to make it work.

I'm still not 100% convinced its a pulley groove shape issue. The angles of the pulley walls seem similar, the only differnece is the bottom of the groove, of which the belt doesn't touch anyway. If I can find a pulley that 100% matches the grooves of our stock ones, and can be used on the GM alternator I'm all for it. But I think all chrysler pulleys were press on weren't they? This one is bolt on. I think I remember someone said they used a toyota truck v-groove pulley on a modern mopar (nippondenso) alternator with their slant, so next time I'm at the yard I'll have to take a look in the toyota section.

I must not have made myself clear. OK, you got it because it was mega-high amperage...what is it you're running in the way of electrically-operated accessories that requires this amount of current?

Ford taurus fan (it blew a 30A fuse after running for a couple seconds) MSD 6a, GM EFI, heater motor, sylvania xtra-vision headlights... well beyond what a stock unit can do at idle.

Dan's right. That is a LOT of alternator ...

It may be a lot of alternator but Pierre is using enough current to make the belt slip. Running a smaller dynamo wont change how much current he uses. The change in pulley size is considerable. You have enough capacity to run at lower RPM and still keep up with your draw. I would try a bigger pulley. Another thought might be Super 6 s serpentine belt setup. The factory serpentine setups are made to get more "wrap" on the pulley for more belt traction. Perhaps figuring a way to get more wrap may help.

How is your EFI project going? I had a real breakthrough on one of my TBI projects this week when I discovered adding a ground strap to the ECU gave me far more consistent sensor inputs and a far smoother running engine.

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Yeah....Im the one who destroyed this rare, vintage automobile.....