Under Drive Pulleys

[Fast94]

I just installed under drive pulleys for my 94 camaro 3.4. Now my battery is under charging. I tried turning the throttle up to raise the rpm's at the set screw, but all that did was make it idle erratic (High when cold, then back down when warmed up). The kit came with 2 pulleys, the alternator and the crank. The alternator pulley is larger than the original and of course the crank smaller. Would it help to put the original alt. pulley back on or is there an idle adjustment/timing fix that will correct my problem or should I bite the bullet and put back on both original pulleys? Couldn't find any topics on it in the forums.

[V8 Killer]

So the crank is smaller meaning its being OVERdriven and the Alt is bigger meaning UNDERdrivin. The crank should be bigger to make it a UNDERdrive pulley. Send it back and buy a more worthy mod other then killing your battery and alternator, making car run hotter due to less water pump rotation, making AC blow hotter at idle and making steering harder out of tight parking spots. To me it just isnt worth the 5 HP at the motor..

[98Camaro3.8]

Originally posted by V8 Killer:
So the crank is smaller meaning its being OVERdriven and the Alt is bigger meaning UNDERdrivin. The crank should be bigger to make it a UNDERdrive pulley.

Almost. On a crank pulley, the principle is reversed. With a smaller pulley one rotation drives the belt less. On an accessory, a larger pulley causes the belt to turn it less. ;)

[V8 Killer]

Originally posted by 98Camaro3.8:
</font><blockquote>quote:</font><hr />Originally posted by V8 Killer:
So the crank is smaller meaning its being OVERdriven and the Alt is bigger meaning UNDERdrivin. The crank should be bigger to make it a UNDERdrive pulley.

Almost. On a crank pulley, the principle is reversed. With a smaller pulley one rotation drives the belt less. On an accessory, a larger pulley causes the belt to turn it less. ;) </font>[/QUOTE]Thank you for clearing it up for me [img]smile.gif[/img]

[98Camaro3.8]

It makes sense when you really think about it.

A smaller pulley has a smaller circumference, so when the crank turns over once, the belt gets moved less. So a smaller pulley is underdriven.

On an accessory, though, the circumference now controls how many rotations are going to occur, instead of the other way around. A 10" (random number) move of the belt would turn a 5" circumference pulley twice compared to a 10" pulley. In this case, a larger pulley is underdriven.

[img]smile.gif[/img]


As for the original question....you may just try installing the stock alternator pulley and see if that gets turned enough to charge.

[V8 Killer]

I just thought it was more the weight than size of the pulley. Since its smaller it has more capacity to spin faster with greater efficency thus overdriving. But I do get what you are saying and it makes sense. I just had it wrong .

[Fast94]

So what I derive from both posts is that I could put back on the original/smaller alternator pulley and leave the smaller crank pulley on, then that would cure my charging problem while still upping my HP. Is that a correct assesment or should I just scrap the pulleys(waited too long to install them, so probably couldn't return them)?

[Fast94]

Thanks I will try that, didn't get the new post until after I posted.

[98Camaro3.8]

Yeah, I would try putting the stock alternator pulley back on. That would still be underdriven, but not by as much. The other accessories wouldn't change. If that fixes the problem, I'd just leave it like that.

[V8 Killer]

See if it helps, if its still running low on voltage. Take them off and replace stock ones. I'm sure you can sell them here and almost make back what you spent.

[Marty85]

I would almost take those pullies off your hands but ive got to have every last ounce of energy from my alternator as it is. Im already pulling about 80 amps continuous from my alternator with my stereo system while cruising. Heck after awhile even while cruising I have to give it a break because voltage will drop to about 12.75. I have to give it a good rest for about 5 min of cruising along to get the voltage back up to 13.5 where it normally sits.

[FunkZ]

Even with just the underdrive crank pulley the alternator still will not charge like before with the engine at idle. It's been awhile but I thought that even with both stock pullies that the voltage output would drop at idle, like 13 or so?

You did realize that these are underdrive pullies, and this is one side effect of using them? That said, I have had my set on for more than 3 years and have not had any problems because of it, I even have a high-power stereo system. If your car idles a lot, such as sitting at red lights, then underdrive pullies are not for you. But if you want a little more performance that will not affect your car as long as the revs stay above ~1100rpm, IMO they are great, I would not do without them.

[SpeedingFirebird]

I have these on my 95 3.4 with no charging problems whatsoever. I do NOT run a high powered stereo system.

[Fast94]

This is for V8Killer & 98Camaro3.8

Thanks for both your inputs. The stock alternator pulley works great with the upgraded crank pulley. With idle @ 1100 rpm I noticed no drastic variations (battery charges fine, just like it did before the change out.[But I can only speak for my car]) when flipping ac on and off, and I have a better response time when i put the pedal to the metal.
I hope this info helps anyone else who's having similar problems. It helped me.

[guy]

where did you get the pullys?