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. Powermaster Conversion Harnesses Part Number Description 136 GM 10Si to CS130D 140 or 150 GM 10DN to 10Si 160 CS130D to CS130 When searching for alternators in the boneyard, be wary of the lug spacing. The opposed pattern (left) is what you want. The CS130 on the right uses an offset lug pattern that won’t work on V8 applications.When searching for alternators in the boneyard, be wary of the lug spacing. The opposed pa Most CS130 alternators came on serpentine-belt applications. If you want to use a CS130 alternator with a V-belt pulley, the easiest way to remove the pulley is with an impact wrench, using gloves or a belt wrench to grip the pulley. Always lay the alternator horizontally to remove the pulley, as placing the alternator vertically could do internal damage. If you don’t have an impact, the end of the shaft is broached for an Allen wrench. Position the Allen wrench on the bench as shown and loosen the 15⁄16-inch nut with a box-end wrench.Most CS130 alternators came on serpentine-belt applications. If you want to use a CS130 al With LS swaps now in vogue, one of the common trends is using the late-model CS130D alternators. The connector is usually labeled PLFS or PLIS. The only wire used is the L position, connected to the charge indicator light on the dash. Do not connect this directly to a switched 12-volt connection, as this will damage the alternator. If a warning light is not used, then you must install a 50- to 80-ohm, 5-watt resistor in series to a switched power source. We’ve seen connectors without the labels, in which case you’d use the third position counted from the large end of the connector. In the photo, you would connect the brown wire to the dash light.With LS swaps now in vogue, one of the common trends is using the late-model CS130D altern Here is a slightly different square-pin adapter from Painless for a CS130 alternator on which the L connector (white wire) should be connected to the gauge light with the S-terminal (red wire) connected directly to the battery-charge wire connection on the back of the alternator.Here is a slightly different square-pin adapter from Painless for a CS130 alternator on wh In adapting a new alternator, the biggest hassle is often the wiring. Powermaster offers several adapters that create simple, plug-in connections between your wiring harness and the newer alternator.In adapting a new alternator, the biggest hassle is often the wiring. Powermaster offers s Once the alternator is bolted in place and charging, you can do a quick test of the charging system to ensure the charging harness is as efficient as your new alternator. With the engine running and the charging system working, read the voltage at the back of the alternator, then compare that with the voltage reading at the battery. If the voltage at the battery drops more than 0.40 volt, it’s usually because the charging wire is too small or there is resistance in the circuit. Our CS130D-charged Orange Peel Chevelle measured an acceptable 0.15-volt difference.Once the alternator is bolted in place and charging, you can do a quick test of the chargi Powermaster tells us that loose V-belt tension is a common problem. An old or glazed belt will slip when expected to drive an alternator charging at 50 to 60 amps, yet it will not make any noise. To test belt tension, place a socket and breaker bar on the alternator nut and turn the alternator clockwise. The belt is the correct tension when the pulley attempts to turn the engine. Why is that important? Because your alternator cranking out 100 amps at 14.5 volts equals 1,450 watts, which converts to 1.94 hp. That means it’s going to take at least 2 hp to drive that alternator through the belt.Powermaster tells us that loose V-belt tension is a common problem. An old or glazed belt Back in the Nov. '09 issue ("Budget Serpentine Drive," pg. 42) we detailed how to convert a V-belt accessory drive to a serpentine system using junkyard parts. The main criteria are the accessory boltholes in the cylinder heads. In our story, the entire serpentine system came from an '80s and early-'90s 4.3L V6 or TBI 305 or 350 truck. We replaced the A/C compressor with a Dorman idler pulley from Rock Auto.Back in the Nov. '09 issue ("Budget Serpentine Drive," pg. 42) we detailed how to convert Above right: The item that usually fails on alternators is the drive end bearing. The quick test is to spin the alternator. If it growls, the bearings are most likely bad. You could rebuild it with new bearings, but you’ll need the correct external Torx fastener socket. Buy a used alternator ($25.00), the tools ($30.00), and new bearings ($27.00), and you will have as much invested as the cost of a rebuilt alternator from Rock Auto. A rebuilt CS130 from Rock Auto can be found for $80.00 without a core charge, but remember there are shipping charges.Above right: The item that usually fails on alternators is the drive end bearing. The quic SOURCES Rock Auto 6680 Odana Road Madison WI 53719 866-762-5288 www.rockauto.com Powermaster Performance 1833 Down Drive West Chicago IL 60185 N/A www.powermasterperformance.com Painless Performance Products 2501 Ludelle Street Ft. Worth TX 76105 800-423-9696 www.painlessperformance.com By Jeff Smith Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!