sold horse,bought ss

ok guys that have done this i need help. i'm not trying to be a wise guy but i need the logic behind why you did the truck alterator swap vs just buying factory replacement. from what i'm reading both are 145 amps so is the truck more durable or is it just a cheaper fix. thanks in advance for the help

blade2222

Stock is only 102 amps.

fleetmgr

Unless you have electrical loads that use up the capacity of the stock alternator, it's a complete waste of time and money. The extra capacity does nothing for you unless you need it. It's like putting a 58mm throttle body on a stock engine.

wssix99

iTrader: (5)

+1 Most of the rationalle I've seen has been, "bigger must be better." A larger part hung off the engine will also cause it to run less efficient.

RPM WS6

iTrader: (3)

The factory "car" unit has been listed from 102 to 105 amps, depending on the source you check.

With stock electrical load there should be no requirement for a bigger unit. There seems to be a feeling amongst some that wiring and alternator upgrades are required even on a stock car just to get adequate charging. This has not been my experience though. I think the issues that many people encounter have to do with cheap/generic alternator rebuilds being poor quality, or batteries that are marginal, or corrosion on ground connection points that creates high resistance over time, or pulley ratios that have been altered, or some combination of the above.

There are some people that have increased electrical demands with aftermarket equipment, such as aftermarket audio systems or other interior gadgets. In those cases, an alternator size upgrade might in fact be necessary.

1 FMF

iTrader: (1)

google alternator output curves, remember the rpm is most likely alternator shaft rpm not engine crankshaft. so you'd have to figure that ratio out, then know what your electrical load is in amps. if it's less than what the alternator can do for the rpm your concerned about, then your ok. if not you either need to raise rpm to get more power (in amps) from the alternator or upgrade to a larger alternator capable of producing that power at that lower rpm. the reason the truck alternator can produce more power is because it's larger- because it's rotor and magnet is larger. the spinning electromagnet is what induces the electrical output from the alternator, the bigger and stronger that magnetic field is along with the stator surrounding it the more power you get.
you'll have to do the math whether you need it or not,
i think most times people are fooled by the stock alternator being weak because it has one or more blown diodes in the rectifier which will make it appear weak.

fleetmgr

Here's a good one showing output v. RPM
https://www.fleet.ford.com/truckbbas...trkelec_06.pdf

However, just because you spin the alternator at 7000 rpm (remember, this is not crankshaft rpm) does NOT mean that the alternator is at full output. Output is determined by load.

Midnight02

iTrader: (8)

My stocker finally gave up and I spent $35-$40 on a junkyard find from a 2004 Chevy Express van. Had 5K miles on the car and the part looked almost like new.

Install was simple -- direct bolt in however it did force me to change belt sizes (may or may not be the case in your instance).

At the end of the day, I can't support the "need" for the truck alternator with any hard data. That being said, I do have a 25% UDP, 4 extra gauges, switches and controls that pull power so there might have been a need and ultimately the truck alternator fixed my charging issues. Not a bad result for what I paid.

Daniel Richards

iTrader: (1)

Hell Underdrive Pulleys alone could very well justify the need for a higher output alternator just to keep the stock amperage output levels.

wssix99

iTrader: (5)

Don't some companies offer replacement alt pullies to compensate for this?

RPM WS6

iTrader: (3)

Going to a higher [max] output unit might not fully compensate for a smaller crank pulley, in terms of idle charging and lost alternator rpm due to a less than ideal pulley ratio. For best charging results, you want a 3:1 pulley ratio for a street car. Keeping this ratio in line would likely do more to help idle charging than any increase in max potential alternator output.

I'm sure someone does, since I believe the pulley used on the Powermaster LS1 alternators is slightly smaller than the OE pulley. I imagine there must be others as well.

Reducing alternator pulley size (to restore the 3:1 ratio) is a good way to cure low idle charging when a smaller crank pulley is used, but you do have to be careful not to spin the alternator past it's rated rpm when doing this. So max engine rpm needs to be considered (especially for cammed engines that are shifted at much higher rpms than stock) as part of this decision.