Just wondering how many amp alternator to go with. It's a street and strip car with a SB400,5 autometer gauges and MSD HEI set up.Also how many is factory?

I just put a 100 amp chrome powermaster one wire in my 67.. No more dimming and thumping lights as I drive around with the music pumped up now. Id give it a 10/10 from me.

Stock is usually 33 to 66 for external regulated ones. I'd go with at least 66 amps.

I recently installed a CS105 alternator, it puts out a little over 100 amps. It works well, but I noticed that when my fan comes on, the voltage is still low (less than 13 volts).

Then, I switched my V-belt pulleys over to serpentine. My alternator now puts out over 14 volts when the fan is on, and over 13.5 when EVERYTHING is turned on. Turns out, no matter how I adjusted it, I could never get the V-belt to stop slipping when the alternator was working hard. The big amp alternators came with serpentine from the factory, and that's the way it should be. Something to think about.

Hey thanks a ton for the help

It DEPENDS. The size alternator you needs depends greatly on what type of modifications you have done to your car that pull power. You need to add up the current draw from electric fans, electric fuel pump, and other electric accessories.

For example: Electric fan - 13A, headlights on high beam - 20A, fuel pump 6A, electric water pump 7A, stereo amp 20A, wipers 8A, and so on. Add all these up and see what you need for alternator output. In this case you would need a high output alternator and the CS 105 would just barely handle it.

The CS 105 conversion is a good idea, but may be total overkill and unnecessary if the only add-on electrical accessory is an HEI.

You also want to look at the RPM the alternator will be turning at cruise RPM. An alternators output is rated at a certain RPM -- look at your pulley size and calculate alternator RPM at the speeds you drive at the most.

For example if your alternator has a 2" pulley and the crank has a 6" pulley the alternator will turn 3 times crank speed. So if you cruise at 2000 RPM your alternator will cruise at 6000 RPM. Look at the alternators current output at 6000 RPM . . . most aftermarket alternator manufacturers will be able to supply this data.

Hope this helps.

I upgraded to an SI12 from a external regulated alt.
I went with 94 amp unit and with a small pulley can maintain over 14 volts with my whole elec. load.
Here is a link to some good alternator articles, also the pros and cons of the 1 wire system

http://207.158.221.52/gw/alt/Alternator_Theory.html

http://www.madelectrical.com/electrical-tech.shtml

I don't have to many electronics, I'm setting the car up to do strictly business no radio etc.I'll check out those sites thanks

CS130. It's compact, puts out decent amperage at idle (not all do), and built like a brick house.

Originally posted by dnult:
CS130. It's compact, puts out decent amperage at idle (not all do), and built like a brick house. Whoops, that's what I have, not a CS105. It's a 105A alternator, and can be found at any parts store.

It's very durable IF you have a good diode pack in it. The cheap ones burn easily, because these alternators get hot quickly due to their small size. Anyway, I highly recommend it.

Just to add a little sanity (not that I have a problem with new alternators, but a hundred amps is a lot of power, you could weld with it...)

My external regulated 61 amp alternator has no problem keeping thing going, evenwith a 660 watt stereo. Course, the stereo's about the only thing drawing any serious power. Like Eric said, add up the loads.

By the way, when you add up the total amperage draw, you need to include a factor of safety of at least 30% (I do 50%). So, if you add up all your current and it totals 40 amps, get a 52 amp alternator. If you draw max current constantly, the diodes will burn or the field wires will short due to the varnish melting.

You can weld with a 100A alternator, but it wont last long! ;)

can't remember which mag, Super Chevy I think has a good article on sizing alternators. It was recent, if you do a search at Super Chevy, I think you will find it easily.

The alternators are considered to be constant current/constant voltage power supplies. They are designed, questionable, to output 14 VDC at engine idle rpm to engine redline rpm at the amperage is required to maintain same, if sensed correctly.

So, in adding up the amps in question, Headlights on, MAX A/C on, wipers on, power window(s) used, in Drive, audio system on, brake lights on, cooling fans on (if equipped), turn signal on, and at engine idle, plus, as Matt suggests, another 30-50% added on, this will be the total load required.