I've been considering upgrading the alternator on my car for a long time anyway. If I was going to do it anyway, I might as well minimize it's neagative impact by installing the underdrive pulleys. Likewise if your alternator is not over stressed, it will not put excessive load on your belt.

Example, my friend drives an Iroc that has an 80 amp alternator. When his electric fans kick on it actually slows the idle down on his completely non computer controlled car because it loads the engine down. Now take any of our cars for example, the fans draw just as much current as his do, yet when they kick on it doesn't load the engine? Why? Because the alternator is working within it's range of efficiency and you are not going to load it significantly more as long as you stay within the proper range.

Now, my car for example, I have a very heavy accessory load, if I'm running EVERYTHING I can actually watch my volt meter dance in time with the turn signal. So, I need a bigger alternator. The 200 amp powermaster unit is capable of putting out as much power at idle as my existing alternator can at full speed. This means that if my current alternator can keep up at full speed, which it easily can, then the powermaster can probably keep up even with the underdrive pulley. Because it was designed with such an output capability it is likely more efficient than the stocker and will thus not put as much load on the engine for any given power output.

It's really all kind of twisted but it likely makes sense if you really think about it. I agree it would be ridiculously stupid to spend $164 on a set of pulleys and then have to spend $350 on an alternator just so you could get back to where you were. However, because I needed the new alternator anyway AND the new one is actually over sized, I can have the best possible situation by getting the pulleys and the alternator.

 

I think the IAC plays a part in this on my L98.

Charging load causes RPMs to drop, IAC pushes the throttle open a bit?

.

 

Sure, if it needs to, but there is a time delay in there. If it loaded your car significantly what you would notice is that when you apply the heavy load, your idle would drop for an instant and then the IAC would open to compensate. Todd's car doesn't do this because it has a carb and thus there is no IAC. My car doesn't do this because the fans don't cause enough excessive load to warrant the change.

I believe the TPI cars had an even smaller alternator so you are probably exactly right and you are seeing what you think you are.

 

I sense a disconnect here.

I'm getting into a zone where I only know enough to be dangerous. But
I'm not sure from what you say that you need more current capacity,
based on what you've described. Not trying to start anything, just making
an observation.

I would suggest that you look into replacing the battery first or at
least have it load tested. It sounds like it is struggling and you don't
want you or your SO to be stranded.

.

 

BTW, I am not trying to argue, just discuss, everything is cool. I appreciate your comments and feedback, discussion is always healthy, arguments rarely are!

Here's the way I look at it. I don't know if it's true or not, but it's the way I justify it to myself. When a component, especially a generator, which is exactly what your alternator is, is operating within it's optimal range, it will only apply create so much drag. Once you exceed that design current, your drag increases very rapidly.

Now to look back at Todd's car, consider this graph



Normally Todd is operating on the red line, on the green line of the graph where drag increases with current in a fairly linear manner. Perhaps it shouldn't say current, but rather say load. Anyway, he's fine until his fans kick on and it throws him way over to the yellow line into the non linear range.

Now, picture a larger alternator, the blue line. In this case he installs the larger alternator which places more drag on the car all the time. He compensates by tweaking his idle speed and everything is good, except that it does now take more power to drive the larger alternator. Now when his fans come on, he is pulling the same current that he was before, but for the new alternator it is still within operating spec and thus is still in the linear range. Yes it applies more load because there is some slope to the drag / current line, but it is not nearly the spike that he would have otherwise seen, and thus is likely not even noticable in terms of engine speed.

If you really are seeing what I think you're seeing in your car, it would be the same effect. As long as you're operating in the green you're cool. When you jump to the yellow your IAC has to compensate. If you had a larger alternator you would cause more drag all the time, but your IAC would compensate automagically and you'd never notice it, then when the fans kicked on you wouldn't notice anything at all either.

There is also the issue of longevity of your alternator if you continually operate it outside of spec. All devices are over built, or at least should be, to provide some factor of safety, but how long can you get by with it before you have trouble?

In my case my existing alternator is likely operating close to the upper end of it's range and needs to be replaced to buy more overhead. Yes that will create more drag all the time but how much in relation to what the underdrive pulley gives me back? Dunno, I'm afraid I don't have any numbers for that one.

 

If you figure out which part # it is for the 200 amp for an LT1 post it Im too lazy to figure it out.. and i feel like buying one !

 

I thought about putting underdrive pullies on my '85 L98. Not sure if it would help much. I'm not really looking to gain power, just help put less strain on the engine. Thanks for the info.

 

It seems to be much better now after upgrading my alternator Nate. Very little rpm drop when the fans come on. Even better since I found out yesterday that the PCV wasn't closing at idle causing a vacuum leak. That was why I couldn't get the carb tuned.

 

Awesome. When exactly did you upgrade the alternator? I know we talked about it. I guess that's how much we get to talk these days huh.

 

I did the alt about 2 weeks ago. If it drops below 13.0v now, I just smack the gauge to fix it

 

We have so got to rip every single wire out of that car and re-do it some day.

 

So much for the Chevron gas mileage test

 

That's done, was finished last month.

 

Probably won't help. Just junk OE gauges.

 

Nathan, which ASP P/N did you order?
I do a lot of high speed driving and I would like to slow the accessaries down.

 

Asp945803

 

But back to Slalom's thought. The battery is the source for the engine. The alternator recharges the battery. Is your battery a higher output than standard? Is it new and putting out maximum?

 

Thanks Nathan!

 

What were the pulley diameters for the crank and alternator? What belt did you use?