Alternator Upgrades - High-output Alternator Tricks On The Cheap

It seems that the biggest growing segment of add-on performance parts for early muscle cars is electrical components. Electric fuel pumps, fans, megawatt stereos, and other amenities all gang up to place a heavy load on the charging system. In the '60s, most cars came with alternators that were more than capable at 40 to 60 amps of output when the biggest load was the defroster fan. Today, it doesn't take much more than a pair of 20-amp electric fans and an 8-amp fuel pump combined with a set of 10-amp headlights to put the hurt on that 60-amp alternator, especially at idle. What generally happens is the charging system voltage at idle plummets below 12.4 volts, discharging the battery. Plus, none of these systems operates nearly as efficiently as it would if the voltage remained constant at around 14 volts. While Powermaster and many other companies offer performance alternators, there are plenty of suitable 100-plus-amp alternator dance partners just waiting for an invitation to a new life in your muscle car.

Here’s a lineup of GM alternators, starting on the left with the original external regulator 10DN, then the internally regulated 10Si from the later ’70s with the serrated end that makes it easy to spot. Third from the left is a CS130 followed by a CS130D with an offset mounting bracket.

Here’s a lineup of GM alternators, starting on the left with the original external regulat

The earliest GM alternators were designated 10DN, employed an external voltage regulator up through early '70s cars, and were capable of around 60 amps max output. The first revision, called the 10Si, placed the voltage regulator internally, but the output remained low. The similar-appearing 12Si pushed output to 90 amps, but it was the move to the more compact CS130 version in the mid-'80s that bumped the output to 100-plus amps. The CS stands for charging system and the 130 is the alternator case dimension of 130 mm. The output curve on these newer alternators also improves low-speed charging instead of relying on increased engine speed to achieve maximum output. The CS130 was followed by the CS130D, which is nearly identical but uses a different, rounded plug-in harness. The CS130D designation remained with the introduction of the LS engines, but GM changed the mounting lug pattern, which unfortunately limits its interchangeability, even within LS engines. While the CS130 upgrade is the most powerful GM alternator and the one to look for, be aware that the lug spacing did change slightly from the standard 6.6-inch distance between the opposing lugs (common all the way back to the 10DN) to a slightly shorter 6.14 inches. This makes adapting the CS130 or CS130D alternators a bit of a challenge with brackets that triangulate the alternator. Using separate lower and upper brackets seems to help with conversions. The CS130 also uses an 8mmx1.25mm thread-pitch bolt in place of the original 5/16 NC fastener. Let's take a look at a few alternators we snagged in a recent yard excursion.