All of the electronic gizmos that afford us excellent drivability and fuel mileage today have been taxing the charging systems of our automobiles for years. And, adding fuel injection, large stereos, or better lighting to those vintage autos can easily exceed the charging capabilities of the factory system. This becomes most obvious during a low-RPM voltage discharge when the alternator isn’t spinning fast enough to keep up with the demand of all those electronics.

This can even happen to factory-stock vehicles. General Motors issued a Technical Service Bulletin (#43-64-07A) dated January 1997, to address low voltage readings or dim lights at idle. The bulletin covered 1990 through ’97 passenger cars and trucks. In basic terms, the bulletin states, “Any vehicle may have a low voltage reading (if equipped with gauges) or lights that dim when electrical loads are heavy at idle, or under very slow driving conditions. This condition may be worse with owner-added electrical accessories or with a discharged battery. THIS CONDITION IS A NORMAL OPERATING CHARACTERISTIC OF THE VEHICLE.”

In short, GM allowed for this shortfall and relied on the battery’s capacity to make up for the difference until the vehicle’s engine RPM increased again. It states that normal driving conditions will recharge the battery and restore the charging system to its normal state. Thankfully, Tuff Stuff Performance makes high-output alternators so this supposedly “normal” condition doesn’t have to be a regular occurrence.

Voltage Drop At Idle

Our C4 Corvette with a second-gen LT1 engine has the benefit of a digital dash. The downside of the increased accuracy of the digital display is that every voltage drop was quickly displayed before our eyes. It exhibited a distinct low-RPM discharge when at idle. While sitting at a red light with the A/C blower on high in the Florida heat, we’ve seen the voltage drop into the 12s with regularity, once the cooling fans turn on. To us, that is unacceptable for a running vehicle with a sufficient charging system. Our 1985 Corvette has been upgraded with later-C4-style dual cooling fans, and the LT1 replaced the factory L98 Tuned-Port engine, but it used a factory Delco-Remy alternator for this application. While GM feels this voltage drop was normal, it has always been unnerving for us, to wonder how low it would go.

Whenever we get caught at a light, the voltage indicator drops. With headlights and A/C on, we’ve seen it consistently into the 12-volt range.

We like driving our C4 and want to be able to enjoy it, even if we need to run the air conditioning and headlights at the same time. The car runs great and has no issues when the engine is driving the alternator fast enough to produce the necessary output to keep everything charged. Everything changes though, when we get to the next red light. String enough of those voltage-depleting stops in a row and we could have an issue.

The Delco-Remy unit (left) served us well, but couldn’t keep up at low RPM. To fix the issue, we contacted Tuff Stuff for one of their 170-amp, high-output alternators. They are all-new construction, available in a variety of finishes, and feature a special grounding tab to ensure your new alternator has the best grounding possible. A necessity for proper charging.

To prevent any issues, we contacted Tuff Stuff Performance for one of their 170-Amp, CS144-style GM alternators. These alternators are available in a variety of finishes, including chrome-plated, polished aluminum, powder-coated, and Factory Cast PLUS+ finishes. Each alternator features heavy-duty copper-wound coils, spike-resistant diodes, and heavy-duty ball bearings, and meets or exceeds OEM specifications. And, besides looking great, they also provide additional low-RPM charging capacity. Just what we were looking for with our C4 Corvette.

A Bolt-In Upgrade For Increased Charging Capacity

One of the best things about these upgraded alternators is that they are designed as a bolt-in upgrade to the factory charging system. Tuff Stuff’s CS144-style alternators output a stunning 170 or 250 amps, depending upon the part number you order. We aren’t adding a lot of other electronics, so we didn’t need the 250-amp version. We just wanted to keep our system charged at low RPM.

One mounting tab on the new alternator is not threaded, so we used a longer bolt and put a nut on the other side of the tab.

Upgrading to the 170-amp alternator was a simple bolt-in application, save for two small details. The small tab on the front of our factory alternator was threaded, whereas the Tuff Stuff alternator was not. We simply found a longer bolt that was the right size and put a nut on the backside.

The other deviation from OEM was the inclusion of a grounding tab on the body of the new alternator. While the alternator may be grounded to the engine through the factory bolts, adding this specific grounding point ensures it gets the best ground possible. As we all know, grounding issues can rear their head in a variety of ways. Many accessory drives are powder-coated, which can also lead to grounding issues if the coating is not removed before installation. Having proper grounding is even more important as you increase the amperage of the alternator and this additional grounding tab bypasses a myriad of potential issues.

It is best to make the grounding circuit out of the same size wire as the charging circuit to keep everything balanced. You can simply ground the alternator body to the engine, or run the ground wire all the way to the negative terminal of the battery for the best ground possible. We ran our wire to the engine and have not seen any issues. We did run a jumper to the battery’s negative terminal and did not see any change in the alternator’s output, so we’ll say our alternator’s grounding is sufficient the way we have it.

Low-RPM Voltage Discharge No More!

With our new alternator installed, we fired up the car to try it out. Our voltage indicator in the dash showed 13.9 volts. When we tested the voltage at the battery, we were happy to see a solid 14 volts at the terminals.

In the hottest part of the day, with the A/C on high and both cooling fans running, the lowest reading we saw on our gauge was 13.5 volts – a far cry from the 12-volt readings we had been seeing previously.

With our new Tuff Stuff alternator making sure everything stays above the discharge line, we’ll enjoy driving our car more when creature comforts such as air conditioning are necessary. The polished finish on our particular unit also encourages us to do a little cleaning under the hood. We’ll get to that when the temperature drops to a habitable level!