Need guidance with alternator selection

I think I have stock alternator in my 1970 wagon. Unfortunately, even on highway with lights and wipers on, it can barely keep up. I will be adding amplifier and powered subwoofers so I need to beef up my electrical system.

Could somebody tell me exactly what type do I need to order from Summit website so I can just swap the existing alternator with new one without any modifications?

My alternator is mounted on the passenger side, has one main red line connected to it plus two smaller wires together in some type of connector. I am thinking that this one is externally regulated alternator, but I am not an expert.

Here are few pics:

picture 1 (http://www.mielko.com/images/car/alt1.jpg)
picture 2 (http://www.mielko.com/images/car/alt2.jpg)
picture 3 (http://www.mielko.com/images/car/alt3.jpg)

Thanks.

So you want a 12SI alternator (SI implies an internal power regulator instead of the old mechanical volatge regulators used on earlier cars) to replace the older style 10DN alternator you have now. You want a 12SI and not a 10SI as it has more out put starting ranging from 56-94 Amps compared to the 37-63 Amp rating of the 10SI model (74 Amps is the most common size). You want to stay away from the 15SI or 27SI found on Cadillacs and Buicks and other larger GM luxury cars for two reasons (first they are off a Caddy so the price jumps because the word caddy was mentioned even though they are available for less money if you say you need it for your pick up). First reason is they are larger so your standard Chevrolet brackets to fit your Chevy won't fit; you have to use a BOP bracket to fit their small block Chevy that they installed (you it still bolts up but you need new brackets). Second because it is a larger size you have more mass rotating which is hard on parts and performance. (by the way most Police cars used a 27SI alternator to keep all of their radios and auxiliary running lights lit with two V-belts needed to power them).

If you need more than 94 Amps you will need to switch up to a CS-130 alternator which is the newer one wire style, remember that heat with an alternator increases as the square of the amperage so the bigger the load the more effort you will have to dedicate to keepig it cool (you do not want the back of an alternator to up against a header tube as that is the inatke for cooling air that is exhausted out the front of the alternator by the fan attached behind the pulley.

Model __________ Output __________ Clock __________ AC Delco
________________ Rating __________ Position _________ Part #

10SI ____________ 63amps ___________ 3:00 __________ 321-39
10SI ____________ 63amps ___________ 9:00 __________ 321-41
10SI ____________ 63amps __________ 12:00 __________ 321-43
10SI ____________ 63amps ___________ 6:00 __________ 321-135
12SI ____________ 94amps ___________ 3:00 __________ 321-266
12SI ____________ 94amps ___________ 9:00 __________ 321-269
12SI ____________ 94amps __________ 12:00 __________ (Lester # 7294-12 Check for interchange)
12SI ____________ 78amps ___________ 3:00 __________ 321-247 or 321-357
12SI ____________ 78amps ___________ 9:00 __________ 321-244
12SI ____________ 78amps __________ 12:00 __________ 321-249 or 321-254

The 3:00 position is the most popular, because it fits passenger side-of-the-engine, stock mounting, with Chevy engines. (The typical long nose water pump arrangement, ’69 and newer.)

Big Dave

Thanks for the reply Dave.

I found these two alternators that are 12SI:

alternator 1 (http://www.summitracing.com/parts/SUM-811005/?image=large)

alternator 2 (http://www.summitracing.com/parts/SUM-810350/?image=large)

I am confused now about the description that states that there is only one wire. So if they are one wire alternators, they wouldn't fit my car without modifications, correct?

Wrong. A one wire alternator has only the large red wire that connects the alternator to the battery (and it needs to be a bigger diameter red wire than what you have now as you will be running more current through that wire with a large CS alternator). The amount of charge and when it charges are decided by the alternator itself, with no other input from the electrical system. When you crank the car up the alternator doesn't do anything until the car revs up above 2400 RPM in engine speed, at which point the alternator starts to charge the electrical system. Another difference with a CS vs. a SI alternator is that the new one wires output their full rated power regardless of engine RPM. With the older model alternators the motor had to rev up to cruising speed to get enough power out of the alternator to charge the battery and power all of the loads placed on it (the lights dim as you pull up to a stop). The CS accomplishes this by putting more wire in the case to get more energy out of the alternator (remember more power creates more heat inside the alternator and the solid state circuits that control it).

You can bolt up a CS in place of an SI alternator the only difference is in the field winding energization circuit (the white and blue wire). The CS uses a four wire connector, but as stated it doesn't need anything other than the big feed wire. The four pack connector allows the alternator to be energized by demand on the charging circuit prior to hitting the 2,400 RPM initialization speed (which once it is activated stays working as it would in a normal alternator). Biggest difference between a CS and a SI is the case (and what is inside it, but in terms of looks it is all about the appearance). The CS is rounded with the SI being much more angular with a sharp edge at the front and back having a flat face front and rear.

Big Dave

OK, I am convinced to go with one-wire alternator. My only problem is that my engine rarely hits 2400 RPM. All gears shift below 2000 and even at 60mph I am cruising with only 1900 RMP on the tach. Does that mean that I would have to connect the four additional wires?

Thanks.

I'm sure you can blip the throttle to get it above that speed as even a big diesel will spin up to 2,400 RPM easily. Once it gets past the initialization RPM it works just fine at any RPM until you turn off the car again. You can also reuse your blue and white wires to cause the alternator to start charging as soon as the car cranks up, it just takes a little work and a four wire watertight connector to plug it in.

Big Dave

Thanks Dave.