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Discussion Starter #1
Just finished the longblock and I'd like to get my 396 fired up and broken in. I'm wondering about the nit-picky stuff though. This will be an engine stand fire up so I don't know what all needs to be in place. Obviously there is no wiring harness. I also need to choose an alternator & starter. Should I replace them with aftermarket stuff from summit or seek out OE stuff?
 

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Hates: Liver. Loves: Diesel
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If its a stock motor, a stock starter is more than enough.

The alternator is little different. Most folks will tell you to go as big as you can saying the more amps the better. I don't really agree with that. Choose an alternator based on what you need. A stock alternator is fine for 90% of what you need in most cars. Alternators only produce what you need which is usually between 10 and 40 amps. During high-draw times like after a jump start it will provide up to its rated amperage.

12si alternator cases (GM's internal regulator alternator for many years) is good for about 90 amps for short periods. If they are made for higher amperage they get really hot. Most of the 12si cases were 45-85 amps and perform well in that range. There are aftermarket 12si alternators available up to 200 amps and they perform just fine during normal operation since they only are providing the 10-40 amps the car needs, but in situations where you are asking for the full amperage like after a jump start or if you've run it half dead with the stereo, it gets screaming hot trying to make that amperage. I have the scars to prove it :)

It boils down to this: if you are running heavy-load items like lights, stereo, or accessories, the hi-amp alternator choices will keep up and be fine since they only have to provide that amperage part of the time. If you deep-cycle the battery every once in a while, stick to an 80-amp alternator at most.

I deep cycle my batteries every once in a while in my RV so I chose a 140-amp 12si alternator. I decided to check on it one day to make sure it wasn't too hot while charging and I burned my hand pretty badly. Shortly after, the alternator died.

Itemize all the loads you have; lights, radio, ignition, everything. W=VxA, so a 55w headlight is 4.6A. A 300w stereo is 25A. Most ignitions draw 3-4 amps. Add up all the amps you could possibly draw at once, mulitply by 0.8 and that's my rule for choosing an alternator. Even during the rare times you are drawing more than the alternator can supply, they'll be quickly replenished in 5-minutes of driving later. 90% of your operation will take place below the required amp draw of the system.
 

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Discussion Starter #3
thanks for the explanation. it's a mild street build up and the only bracketed accessory should be the alternator. no AC, no power steering. eventually i'll put in a small stereo and the only other constant draw will be the headlights and gauge lights.
 
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