SL-C Wiki

There are many alternators on the market, with varying sizes, types and capacities.  This page is intended to give an overview of the topic, to help you choose the right alternator for your SL-C.

Alternator Types

Most production cars use what is loosely termed a 3-wire alternator.  Such an alternator has the usual power output post, but also one or more wires that typically are used to excite the windings. These act as a signal to the alternator to start producing power.

In the past couple of decades, the 1-wire alternator has made an appearance.  It's key benefit is easier wiring, at the expense of control, and normally, some delay in output based on RPM. Many 1-wire alternators do not provide sufficient power output at idle, and so extended periods of idling can quickly deplete your battery.

Either one can be made to work on the SL-C.  Here's a chart to help understand the differences.

For almost all builders, a 3-wire alternator is the correct choice.  

A 1-wire alternator may be an acceptable choice in a pure race car that will experience no significant idling, and which may not have an engine harness that is capable of controlling an alternator.

Alternator sizing

Alternators are available in many physical sizes. Depending on the situation, you may have enough room for alternators with larger cases, or may be limited to a smaller form factor.In most cases, any alternator that will fit and allow easy access for service, belt changes, etc will be fine from a size perspective.

The most popular sizes for GM alternators are the older CS-144 cases which are larger than the current CS-130 size cases.  

Larger cases sometimes allow for better air circulation, and hence better reliability, as well as allowing for bigger windings and roughly speaking, more power (though there are plenty of small, high-power alternators available).

A larger case will sometimes also allow for more rectifiers, allowing a smoother DC current, in those cases where you have electronic equipment that is very sensitive to power waveforms (even though the output power of an alternator is DC, that DC power is rectified from the AC power that the alternator natively generates, and more and better rectifiers can produce smoother power).

The takeaway is that any case size will suffice that fits, and offers you the desired capacity, degree of rectification and other requirements you may have.

Alternator Capacity

The most common question about alternators when building an SL-C is "how many amps do I need?"

The answer, of course, is "it depends".  (Did you see that one coming?)

A good rule of thumb in sizing alternators is to calculate the max load your car will demand, and add a safety factor, like 10 or 20%.

You can calculate how much your car needs by making a list of every electrical load in the car, and totaling them to get the max load the alternator could be expected to serve, and add a fudge factor. That's doable if you know your loads, and can do that.

For most people, however, it's easier to interpolate a figure from what seem like similar cars.  For example, the C6 Corvette has a similar load profile (actually, a higher one than most SL-Cs), and so using the same capacity as that car probably represents a reasonable number for most SL-Cs.

Of course, if you plan to have a 1000 watt amplifier, a resistance heater, and heated seats, you may want to go big. :)

In summary, most SL-Cs will do fine with an alternator in the 130-150 amp range, with track cars able to drop that down to 90-110 amps.

So which alternator should I buy?

If you are using the factory front dress kit for the LS-series engines, and you don't have abnormal demands on the electrical system (megawatt amplifier, etc), order the 321-1811 alternator. It's available from most all parts stores, eBay and alternator specialty stores as well. It was used on the 2001-2005 Chevy Silverados, among many others. At the time this was written, prices were hovering around $80-90.