I have a 3G series alternator, but I'm not sure if it's large case or small case. How can I determine the case size?
An easy way to see if you have a large or small case alternator is to check the holes on the front, near the pulley. This is called the drive end, and on small case alternators there are four small holes per each of the three ribs radiating from the center. On the large case, there are only two holes on the same ribs. Above we have an overlay of the two housings The upper left of the image is the larger unit and the holes are highlighted red. The lower right shows the smaller unit with its holes highlighted blue. Stock 3G units usually had an output of about 90 amps, the larger ones puts out about 130 amps. Our 3G series large case alternators start at 130 amps and go up to 250 amps with our Quicktifier Dual and Triple Rectifier System.