AFTERMARKET GAUGES

Looking for instrument gauges?

By Wayne Scraba / Photography by Wayne Scraba

It’s a flashback for me. Sitting in the showroom of the big city Chevy dealership is a brand spanking new 1970 Malibu SS454.

The car is pretty much perfect. It has a cowl induction hood, turbo 400, limited slip, and a gorgeous white/black bucket seat interior. It includes all sorts of options including esoteric stuff like a map light in the rear view mirror and a neat indicator lamp that reminds you when the windshield washer fluid is low. Cool huh? But wait – there’s more (or perhaps “less”) – the only instruments on the panel are the speedometer and a fuel level gauge. Wow. Weird? Not really. Plenty of factory hot rods were actually built that way. (That car eventually ended up with an 8,000-rpm Sun Super Tach clamped to the steering column, but I digress.)

Gauges are incredibly important in a musclecar. That’s a no-brainer if there ever was one, but is there really a difference between gauges? There certainly is, and when it comes to information about your engine (and in some cases, the drivetrain pieces behind the engine), the more accurate your information and the easier it is to decipher, the better off you’ll be. Just as important, there have been major developments on the gauge front in the past few years, and what was hot technology a few short years ago, could prove to be old news today.

What’s Best?

So what’s hot and what’s not when it comes to aftermarket instrumentation – particularly, which is better, mechanical, electric or the latest stepper motor instruments? The answers might surprise you. All three configurations can be built into an accurate gauge; but the truth is, the determining factors more involve installation and application than gauge accuracy. For example, some of today’s stepper motor configuration gauges combine the ease of electric gauge wiring with a full sweep dial face like the mechanical gauge. What follows is a short list of advantages that should help you to make the decision for a specific application:

Mechanical Gauge Advantages

Mechanical gauges have a full 270-degree sweep which makes them easier to read accurately. Mechanical gauges do not require 12V power to operate. They make direct physical contact with the item they are reading. Obviously, this is accomplished through tubing or lines, which eliminates the need for electric signals. Mechanical gauges are ideal for vehicles that operate on voltages other than 12V, with no voltage at all (magneto applications) or operate on a battery with no generator.

Electrical Gauge Advantages

Electrical gauges have a 90-degree sweep. They do not have large connectors and tubing coming out the back of the gauge. Given the design, they can be mounted in more unusual positions without connections showing. The design allows them to be easily installed in tight areas. It’s also easier to install the gauge a great distance from the item being measured (which may be important in certain applications). An electric gauge also prevents fluid from entering the passenger compartment.

Electronic Stepper Motor Gauge Advantages

Stepper motor gauges have a full 270-degree sweep like a mechanical gauge. Like electric gauges, they do not have tubing or large connections originating behind the gauge. Additionally, the configuration of the gauge allows it to be mounted great distances from the source if necessary. They tend to be shallower than either older electric instruments or mechanical versions. That makes them easy to mount in tight confines. Finally, some companies manufacturing electronic stepper motor gauges offer a huge array of options such as integral warning lamps, in-gauge turn signal indicators, tachometer shift lights and so on.

Gauge Sizes

Most manufacturers offer at least a couple of different sizes when it comes to gauges. Typically, they either have a 21/16-inch face or a 25/8-inch face. Anything smaller is tough to read and anything larger is often difficult to package. When it comes to tachometers and speedometers, the normal sizes are 33/8 inches and either 4½ inches or five inches in diameter. Some companies though, offer gauges in other size ranges. For example, you can get tachs as small as 21/16-inches. They’re not easy to read (especially for us old guys), but they can be fit into tight locations.

As we pointed out above, instruments with the shallowest mounting surfaces are today’s electronic stepper motor models. They’re considerably smaller (from a depth perspective) than other gauges.

So far so good, but what are the most common instruments someone with a vintage musclecar should look at? Check out the following photos for a look at the most common.

Information age: This is a look at the completed cluster. As you can see, it includes the Revolution gauges mentioned below, along with a matching speedometer, fuel level gauge and transmission temperature gauge. Options for the various instruments are considerable. You can select gauge lighting colors and styles, various integrated warning lamps, high beam and turn signal indicators, and more. They even offer custom faces, which allow you to tailor the instrument to your car.

1 Eye test: When it comes to gauges, bigger is usually better (up to a point). If possible, install a tach with the largest practical face. Before drilling any holes in the dash, sheet metal or tubing of your musclecar, take the time to move the tach to several different locations. That way, you can buckle yourself into the driver’s seat and with the help of an assistant, see which tach location is the most comfortable for you. By the way, this Revolution tach measures 33/8 inches in diameter.

2 Come to the light: Two important considerations when buying a tach are the rpm range on the face and a shift light feature. A tach that reads to 12,000 rpm might be perfect for a high-winding, small cubic inch, strip-only motor, but it certainly isn’t practical on a near-stock 454 that will never see the other side of 6,500 rpm. What’s needed here is a tach face that’s maxed out at 8,000 rpm or so. As far as shift lights go, there are a number of different versions on the market, but this Revolution tach has a neat trio of integrated shift light indicators. When the engine (and tach) reaches the shift point, then the LEDs illuminate in sequence.

3 Under pressure: One instrument that is absolutely critical in any car is the oil pressure gauge. There are a number of different oil pressure gauges on the market, but one consideration is the overall range of the gauge. For example, you can find gauges manufactured in 0-100 psi and 0-200 psi range. You can also find gauges marked with metric BAR readings instead of psi, but we suspect most of you prefer good old-fashioned psi readings. Which gauge is right for your application? It depends upon the engine. If your musclecar will never see the high side of 70 psi, then it makes no sense to install a gauge that will read 200 psi.

4A & 4B Plumbing skills: Oil pressure gauges found in motorsports were, at one time, almost exclusively mechanical. They were the darlings of the racing community. Plumbing was always a pain, simply because the plastic lines most cars were fitted with could prove downright dangerous if not installed properly, not to mention illegal in the eyes of most race sanctioning bodies. For those examples, plastic hose doesn’t cut it. One of the best ways to plumb a mechanical oil pressure gauge is by way of braided stainless steel line. On the other hand, a modern, high-quality stepper motor gauge (like the Revolution gauge shown here) is plumbed by way of pre-assembled cabling. It routes easily without fear of rupturing a pressurized line (which doesn’t exist in an electronic instrument).

5 Be cool: Probably the second-most critical instrument in your arsenal is the water temperature gauge. It’s no secret that once the temperatures creep out of sight, then only will an idiot light beam brightly. A quality gauge is the answer. There are a lot of different combinations (of face calibrations), but the most common is one that reads from 120 degrees to 260 degrees (or so). While some electrical (or electronic) water temperature gauges with wide temperature calibration mandate some form of add-on blackbox to function, that isn’t the case with a stepper motor-based instrument. Here, the gauge hooks up much like a conventional electric gauge (wiring harness from the gauge to a sender).

6 Adapters and sensors: When dealing with any water temperature gauge, the basic temperature probe should be located in the water jacket or on the intake manifold water crossover. In a typical installation, some engines require a ½-inch NPT adapter nut for the probe installation; others require a 3/8-inch NPT adapter. Once the adapter is installed, insert the sensor and carefully tighten the sealing nut. A coating of anti-seize compound on the sealing nut is a good idea. Don’t over-tighten the nut. Typically, you should tighten a 1/4 turn beyond snug to make the connection. What you see here is the high-tech sender harness used in Revolution gauges.

7 Voltmeter vs. ammeter: Another instrument that’s very important is a voltmeter. Why use a voltmeter instead of an ammeter? Technically speaking an ammeter is actually a “flow meter” of sorts that measures current flow to the battery (under normal conditions) or discharge from the battery (in the case of alternator system failure). With an ammeter that means the entire alternator output used to recharge the battery must first be routed through the ammeter under the dash (which translates into large, potentially hazardous wiring). On the other hand, a voltmeter works like a fuel pressure gauge — but instead of measuring fluid in PSI, the voltmeter measures electrical system pressure in volts. A voltmeter only needs to tap into a circuit. Voltmeter installation is easy, quick and safe: It hooks up to a fused, ignition-switched “off/on” source.

8 Respect the fuel: In racing, fuel pres- sure gauges are as common as oil pressure gauges; however, they’re not that common on the street. If you’re thinking about adding a fuel pressure gauge to your musclecar, give it careful consideration. Because raw gasoline is found in the line running between something like a mechanical gauge and the source, a fuel PSI gauge should never be mounted inside the vehicle. There are three exceptions to this rule: A mechanical gauge with an “isolator,” an electric gauge or an electronic gauge. Reliable electric and electronic stepper motor fuel pressure gauges such as this example are relatively new. They incorporate an electrical sender plumbed within the fuel line and then incorporate good old-fashioned wires to transmit the information to a cockpit-mounted gauge.

9 Thin is in: This is one reason why today’s electronic stepper motor configuration instruments have become the norm in Detroit-built passenger cars: They’re extremely thin, which makes packaging a bunch easier.10 Easy mount: A simple innovation this writer is fond of is the mounting arrangement engineered by the folks at Speedhut (makers of the Revolution series gauges). As you can see, the case is threaded. A large ring simply threads on the backside. This is a secure, simple and effective answer to mounting gauges.

11 Rear view: Speaking of mounting gauges, here’s a good look at how a Revolution tach installs in the back of a custom GNX cluster (for this writer’s Buick).

12 Slim harness: Piggyback wiring harness assembly for lighting multiple gauges. It definitely simplifies the potentially large wire bundle on the back of a cluster.

13 Teamwork: Here’s the backside of the new cluster before the harness was tidied up. Once the piggyback light harness (and a similar harness for the power wires) is installed, the wiring actually becomes simple.