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AEM alternator pulley...which belt???
- Thread startermr.mitsu
- Start date
strokin4dr
Well-known member
Is it a stock size pulley or an underdrive piece? This shouldn't be too hard to figure out. Does the stock size belt not fit? If not, try one that is a little bigger.
Napa has assortments of alt belts but I would stick with a stock pulley.
ya i would replace it with a stock.. larger the pulley the alt. will not be able to keep the voltage up. Here is a example.. for every 2 times a stock pulley spins the aem will only spin once. These cars allready have voltage issues as i added more ground staps and a 4gage ground cable along with the stock wimpy one and when the head lights or windows are used i get a nice idle drop and a diming effect and my alt charges at 14.2 volts.
It is just going to create less of a pull on the rest of the rotating assemly, and create < the standard 14.2+/-V the car normally generates under load.
I wouldn't worry unless you have a "system" in your car.
I wouldn't worry unless you have a "system" in your car.
When making "big power" people strive to get an much voltage as possible and you are doing the opposite. Some mods work well for these cars, this is not one of them. The charging systems are not the highlight of these turds and weakening and already weak link isn't good business. I would stick with stock. If you want a few HP yank the power steering belt at the race track.
^^ what polish said.. or just turn the boost up. I would deffently ditch that aem pulley before you start ending up with a dead battery.
Dialcaliper
Well-known member
Eh? There's no way it's a 2:1 reduction from the stock pulley. In order for that to happen, the pulley would have to be twice the diameter of the stock one. (somewhere between 7-8 inches). Most underdrive pullies are no more than 10-15% larger. Combined with an underdrive crank pulley, you might be able to get 25-30%, which is probably too much for anything but a race car.
If you run huge cams and have set your base idle higher than stock (950-1000 RPM, stock is 850 on the VR-4), a little underdrive is perfectly reasonable, but otherwise I would avoid it. The low voltage problems are typically at idle or low RPM anyhow (at anything above 2000RPM, the regulator starts limiting the output). On the other hand, if you intend to raise the rev limit above 8500 or so, underdrive is actually a *good* idea, especially on the water pump (which can start cavitating when overspun, which hurts flow and can damage the pump).
Typically, it's best to run the accessories in the same range of rotation speed that they normally operate. Underdrive pullies are best used to correct the speed on an engine that both runs and idles faster than normal. "Freeing up power" is really a secondary benefit. If you really must have lightweight pulleys for better throttle response, you're better off sticking with stock diameter.
If your goal is to "free up power" with light pullies, you're better off just ditching your A/C and fitting a less powerful alternator (The car comes with a 90A - get a 75A from a DSM for example).
Quoting chris:
ya i would replace it with a stock.. larger the pulley the alt. will not be able to keep the voltage up. Here is a example.. for every 2 times a stock pulley spins the aem will only spin once. These cars allready have voltage issues as i added more ground staps and a 4gage ground cable along with the stock wimpy one and when the head lights or windows are used i get a nice idle drop and a diming effect and my alt charges at 14.2 volts.
If you run huge cams and have set your base idle higher than stock (950-1000 RPM, stock is 850 on the VR-4), a little underdrive is perfectly reasonable, but otherwise I would avoid it. The low voltage problems are typically at idle or low RPM anyhow (at anything above 2000RPM, the regulator starts limiting the output). On the other hand, if you intend to raise the rev limit above 8500 or so, underdrive is actually a *good* idea, especially on the water pump (which can start cavitating when overspun, which hurts flow and can damage the pump).
Typically, it's best to run the accessories in the same range of rotation speed that they normally operate. Underdrive pullies are best used to correct the speed on an engine that both runs and idles faster than normal. "Freeing up power" is really a secondary benefit. If you really must have lightweight pulleys for better throttle response, you're better off sticking with stock diameter.
If your goal is to "free up power" with light pullies, you're better off just ditching your A/C and fitting a less powerful alternator (The car comes with a 90A - get a 75A from a DSM for example).
Quoting chris:
ya i would replace it with a stock.. larger the pulley the alt. will not be able to keep the voltage up. Here is a example.. for every 2 times a stock pulley spins the aem will only spin once. These cars allready have voltage issues as i added more ground staps and a 4gage ground cable along with the stock wimpy one and when the head lights or windows are used i get a nice idle drop and a diming effect and my alt charges at 14.2 volts.
Quoting Dialcaliper:
Eh? There's no way it's a 2:1 reduction from the stock pulley. alt charges at 14.2 volts.
sorry sir if you read i said "as a example" jesus.
seee
Quoting chris:
Here is a example.. for every 2 times a stock pulley spins the aem will only spin once.
Eh? There's no way it's a 2:1 reduction from the stock pulley. alt charges at 14.2 volts.
sorry sir if you read i said "as a example" jesus.
seee
Quoting chris:
Here is a example.. for every 2 times a stock pulley spins the aem will only spin once.
Last edited by a moderator:
cOmpressor
Well-known member
Well his screen name is "Dialcaliper" not "dang old measuring measuring stick thingy" /ubbthreads/images/graemlins/rofl.gif
Dialcaliper
Well-known member
Sorry if you took personal offense, it was not intended. I wanted to point out the % numbers mainly to illustrate the use of pulleys for correcting accessory speed with high idle/high RPM motors.
I'm just another pesky engineer that someone let too near a bunch of books and some precision measuring equipment.
Related to the original question, you can tell if the pulley is underdrive simply by measuring the diameter, and divide by the stock pulley diameter. (if for example, the ratio is 0.90, that's a 10% underdrive)
Quoting chris:
Quoting Dialcaliper:
Eh? There's no way it's a 2:1 reduction from the stock pulley. alt charges at 14.2 volts.
sorry sir if you read i said "as a example" jesus.
seee
Quoting chris:
Here is a example.. for every 2 times a stock pulley spins the aem will only spin once.
I'm just another pesky engineer that someone let too near a bunch of books and some precision measuring equipment.
Related to the original question, you can tell if the pulley is underdrive simply by measuring the diameter, and divide by the stock pulley diameter. (if for example, the ratio is 0.90, that's a 10% underdrive)
Quoting chris:
Quoting Dialcaliper:
Eh? There's no way it's a 2:1 reduction from the stock pulley. alt charges at 14.2 volts.
sorry sir if you read i said "as a example" jesus.
seee
Quoting chris:
Here is a example.. for every 2 times a stock pulley spins the aem will only spin once.
Last edited:
