In the early muscle-car days, an alternator capable of 60 amps was considered more than enough to handle the meager electrical demands of a point-triggered ignition system, a 20-amp defroster fan, and a pair of headlights. But today, with EFI, current-hungry electric fans, high-demand nitrous solenoids, big stereos, and other electrical accessories all creating a watts riot, 21st century charging system standards have escalated to 100 or more amps from that same alternator. So if you haven't already done it, now is a good time to take advantage of all this OE electrical power that's just sitting in boneyards. This article will focus on how easy it is to integrate these new alternators into your older muscle car with emphasis on the electrical side of these conversions. Mounting the alternator should be easy since most of these alternators use the same basic mounting lug orientation. When junkyard hunting, look for an alternator with mounting bosses configured in the same orientation as your alternator. With the alternator mounted, we'll show you how to wire it.
The first GM 10DN alternator appeared on the '63 Corvette and used a remote-mounted voltage regulator. These alternators were rated around 40 amps and are prime material for an upgrade. The 10 and 12 SI alternators were the second-generation units and are generally the same size with similar mounting bosses. SI is an acronym for systems integrated because the voltage regulator was moved inside the alternator. GM built millions of these units from the '70s until the CS130 debuted in 1986. The CS (charging system) alternators offered a generous increase in idle amperage output (generally around 80 amps) with maximum output around 100 to 105 amps. This is an important point. Early alternators required high rpm to achieve maximum output, while late-model versions can achieve 90 percent of maximum output at idle. The CS121, CS130, and CS144 numbers refer to Stator diameters as measured in millimeters. The most popular are the CS130 alternators with a case diameter of 5.12 inches. The CS130D is also slightly larger than the CS130, but the mounting lugs are the same. As case diameter increases, this creates more room for additional wiring and larger rotors, which increase output. Because the CS144 is larger (5.9 inches), it is capable of roughly 140 amps of max output. Keep in mind that as output capacity increases, so does heat. Another little-known fact is that the integral fans pull air through the alternator from the rear and exit the front. This means keeping the rear of the alternator free of obstructions will improve alternator life. We've listed several companies that offer adapter connectors, or you can also wire them yourself using replacement factory connectors and save some money.
The whole idea behind adapting a larger alternator is to provide a bunch more amperage when demand is high. This means that in addition to the alternator, a larger charge wire that connects the alternator to the battery is necessary. Generally, a 6-gauge charge wire is necessary to handle more than 100. A good test of resistance is to measure the voltage at the alternator output terminal with the engine running. Then measure voltage at the battery. If the voltage difference is less than 0.50 volt, then the charging wire is a sufficient size. If the voltage drops more than that 0.50-volt number, the charge wire is too small and needs to be upgraded.
Parts List
Description PN Source Price Powermaster 10SI to CS130D 136 Summit Racing $22.97 Powermaster GM 10D to 10SI 140 Summit Racing $20.97 Powermaster CS130D to CS130 160 Summit Racing $25.97 Painless CS130D adapter 30705 Summit Racing $24.97 Painless CS130 adapter 30707 Summit Racing $18.97 M&H 10DN to 12SI kit 27555 M&H Electric $21 M&H 10DN to CS130 37787 M&H Electric $21 10D alternator connector S84 RockAuto $2.33 10SI alternator connector 85841 RockAuto $1 CS130 alternator connector 1929 RockAuto $6.23 CS130D alternator connector 1235 RockAuto $9.02
A late-model GM alternator conversion like this CS130 can really pump up the charging system on older cars. With two 20-amp electric fans, a 10-amp electric fuel pump, and the headlights operating, the voltmeter indicates the alternator is still capable of delivering 14.6 volts. Our experience with a ’60s GM 10DN under this same load delivered barely 11.5 volts.
