I've been doing alittle lookin for a new bolt-on and I've decided on an underdrive pulley system.........What do you guys think I should get, just the crank pulley or a set that included crank, alt, water pump, etc?

I've read that with the crank and alt pulley set up some people have problems charging at idle or low speeds. Is this true............anyone with them please gimme your experiences with different set-ups.

Thanks again

 

Well, I had chargin problems with just the smaller crank pulley, but I think that was mainly due to the fact that I couldn't run one of my belts so it was putting a strain on other things in the process, though all acc's still spun.

 

I personally think there a waste of time. I've heard of over heating from water pump speed slowing and low charging at idle and low rpms. Not worth a damn in my book.

 

I makes perfect sense how they'll give you power, it's the same principal as using an aluminum driveshaft- less rotating resistance. If you get the high performance set then your charging will not be as high when you are stuck in traffic with your radio on, lights on, and your engine idling in gear at 500rpm. As soon as you reach 700rpm your volt meter goes up and you're fine. I used them for over a year and never needed a jump and maintained 170 degrees unless stuck in traffic with zero airflow, but I have this thing called an electric fan that comes on when that happens. I wouldn't waste my time with the ones that come with an "overdrive' alternator pulley (power and amp) to compensate for the underdrive- defeats the purpose if you ask me.

 

Actually smaller pulleys turn whatever accessories slower and the power you gain is from reducing the losses associated with mass rotational dynamics. If you turn it slower, it requires less energy. That power now can be transfered to output, rather than being consumed by other mechanics. But there is a compromise....

You gain some usable power, but at what cost? Higher operating temp, dimming lights at stop sign and stop lights and at night what happends if the temp comes up (both ambient and operating) and the fan comes on? All in all, you will be applying more strain on the systems required to maintain correct operation of you car, unless you run at 4,500 RPM or tap the throttle at the stop sign to keep the charging system up under high load (such as driving at night).

For a car driven on the street as a primary vechicle, I would probally say no. For a weekend hotrod....well, do you live with the dim lights at a stop light and the slight possibility of a higher running temp? Thats up to you.....I have that same compromise with my ride and I dont mind, but I dont drive it everyday.

 

Even with underdrive pullies, wether you are at 900rpm or 4500rpm your alternator is putting out the same 13.(whatever) volts. It's internally regulated so it doesn't exceed that. I agree with chacane67 on everything else though.

 

You sure? I know when I've had charging problems, bringing up the rpms help the problem.

 

I know I shouldn't trust the integrity of the factory volt meter, but the charging charachteristics of my alternator with March #4000 pulleys looked something like this-

(warm)idle in neutral with no acessories- 700rpm- charge rate over 12 volts

(warm)idle in gear with acessories on- 500rpm- drop to zero charge

(warm)driving with acessories on- 900rpm- full charge

(warm)driving with acessories on- 4500rpm- full charge

I dispatch for AAA and I know for a fact when my drivers battery boost a members car they are advised to "drive it around the block" to charge the bat. The only answer I have to that is "to each his own". When I can see my volt meter pointing as high a it ever did even while the car is at 900rpm, I am convinced that the alternator is putting out full amperage and reving it higher is a waste of fuel.

Now, take higher loads into effect. Have you ever jump started another vehicle using your own, running vehicle? As the disabled vehicle's key is turned, your engine rpm dies down, and so does your volt meter. You are taking amperage directly away from your own charging sysem. You can actually make the OTHER vehicles motor crank faster by revving your own engine. In this situation, the higher rpms will produce more charging etc. I think if you have a "normal" stereo in your car and a competant alternator, high performance pulleys work fine for you.

This has just been my experience with my own vehicles, maybe both of them were exceptions to the rule?

 

There is a specific RPM that is necessary for the regulator to switch on for charging. If you go under the required RPM, the alternator will not charge.
If you underdrive it too far, and/or your nice camshaft throws a lopey idle into the situation, it will not charge below the required RPM. Thus, you will experience such charging problems.

 

I put underdrives on mine, notice charging problems also. Fuel injected cars have more problems with them too. When the voltage drops at idle, the pulse width will be longer resulting in a rich condition. Unless you can correct this in the chip. You MIGHT see a little gain at the track, not on the street. Would I buy them again? NO