Alternator pulley size question

[staged67gspwr]

I went from a 2 3/8 diameter alternator pulley to a 2 3/4 will this affect anything?



Thanks

[Yoda4561]

It'll underdrive the alternator slightly, so the alternator won't have as much output at idle as it would with the smaller pully, but also won't load the engine as much. As long as you don't have charging/electrical issues with the larger pulley it should be fine. If you do have issues you may want to swap the old one back on.

[staged67gspwr]

Ok Dan thanks,i`ll check out my voltage reading at idle,should be 13.5-14 correct?

Thanks

[TnBlkC230WZ]

You really need to know the size of the crank pully. normall ratio is the crank pully is about 3X the alt pully.

[H2Ogbodies]

Ideally, you want 14.4 @ the alt. charging post. Given the amount of voltage drop you will encounter throughout the vehicle, your operating voltage must remain high-13.5-14V is not enough. Low voltage combined with high amp draw creates problems for both safety and for component performance. Lower amp draws can be managed with a higher voltage-keep this in mind when designing a charging system.

[MonzaRacer]

Sorry to burst most peoples bubble but charging systems are not tested at idle then get a test at idle then the difference between idle and "2000" or off idle test are compared and also the ripple means a lot too.
If you can get 13.5-14 volts at idle, and it not pull down lower with say a fan or other sudden draw you good.
Most GM/Ford specs are 13.9 to 14.6 volts as tested.
Ripple current can be tested with volt meter on AC volts scale in the 500mv to 2 v/ac scale.
Steady reading for good new alternators should run 0-50 mv ac across the battery terminals, and if you flip a load on say high beams or fans to high etc the reading shouldnt jump above 50 mv/ac.
Now if you have a used alternator you can accept up to 80mv ac jump under electrical load if it goes over 100 mv/ac figure its got a weak diode, think about replacement at earliest convenience. if it goes over 200mv/ac its done and riving any more than to go get new one can cause electronics/battery damage over time. if going over 250mv/ac its gonna cause a battery fialure sooner than later, the cheaper the battery the lest likely it will die an immediate death. high end high cca batteries especially like Optimas and such will not live long with bad diodes in alternators.
Oh and newer cars alternators like the CSI GM alternator should hold in the lower range below 40mv/ac.
Some comapnies also sell parts to up grade specific alternator bearings, stator(part that makes amperage rating) and better regualtor cooling.
If you get 14v/dc and up you good as long as with a load turning on it doesnt drop a lot and stay down.
Lee Abel
AFTERMARKET PERFORMANCE

[TnBlkC230WZ]

Which altenator are you running? We really don't know what is proper idle voltage until we know the load and altenator.

[staged67gspwr]

Which altenator are you running? We really don't know what is proper idle voltage until we know the load and altenator.

I have 140 amp powermaster alternator,i got one of those billet pulleys and switched out the original which was smaller thats why i was asking.

Thanks

[TnBlkC230WZ]

CS or Si altenator? They make both. Monza racer is correct. Most altenators don't put out max power until about 2000 RPM engine speed which is 6000 RPM Alt speed if you are running a 3x pully ratio. That is why it is important to know which altenator and what pullys. The CS will make more power at idle, but probably not more than 50% of max. So if you are capable of 60 amps at idle you will hold 14 +/- volts until that Taurus fan turns on high. Then your voltage will go down because the altenator can't keep up. This is normal.

[staged67gspwr]

I have the Hot Rod alternator 140 amp part # 37293,it usually comes with the 2 3/8 pulley but i replaced it with those billet aluminum ones with the nose cap which look really nice but the pulley is 2 3/4,my crank pulley is 6 1/4 diameter and water pump is 6 3/4 diameter,im not running electic fans,what do you think?

Thanks

[Jim Nilsen]

If you are running an aftermarket EFI system like an Accel DFI you definately need to make sure you have the right amount of voltage at idle as it will cause decay in the injector firing causing rough idle. Factory EFI setups are more forgiving I have been told in my research.

[staged67gspwr]

If you are running an aftermarket EFI system like an Accel DFI you definately need to make sure you have the right amount of voltage at idle as it will cause decay in the injector firing causing rough idle. Factory EFI setups are more forgiving I have been told in my research.

No FI, carb engine checked it a few days ago its charging fine at idle.

Thanks