What To Look For In Aftermarket Gauges
Spin the clock back more than a few decades. In my neck of the woods, it was common (almost mandatory) to have a Sun Tach bolted to the dashtop of a hot rod or race car. Under the dash was either a trio of Sun or Stewart Warner gauges. Those gauges included an oil pressure gauge, a water temperature gauge and an ammeter. The ammeter was obviously electric but the other two were usually mechanical.
It worked and it was (and it still is) incredibly important to have gauges in a modified car. But times have changed. When it comes to information about your engine (and in some cases, the drive train 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. Thanks to the folks from Speed Hut (http://www.speedhut.com) – manufacturers of the Revolution series gauges shown here — for sorting out the latest in performance instrument technology. Check it out:
What’s Best: Mechanical, Electric or Electronic Stepper Motor Gauges?
So what’s hot and what’s not when it came 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 should help you to make the decision for a specific application:
Mechanical Gauge Advantages…
Mechanical gauges have a full 270° 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° 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 prevents fluid from entering the passenger compartment.
Electronic Stepper Motor Gauge Advantages…
Stepper motor gauges have a full 270° sweep such as a mechanical gauge. Like an electric gauge, 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. Modern examples tend to be shallower than either older electric instruments or mechanical versions. That makes them easy to mount in tight confines. Finally, some companies such as Speed Hut 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 2-1/16-inch face or a 2-5/8-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 3-3/8-inches and either 4.5-inches or 5-inches in diameter. Some companies though, offer gauges in much larger size ranges. For example, you can get tachs as small as 2-1/16-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 you should consider? Check out the following photos for more. In addition keep your browser pointed to Racing Junk and watch for part 2 of the series:
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 car, 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 3-3/8-inches in diameter. 
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. 
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 engine will never see the high side of 70 PSI, then it makes no sense to install a gauge that will read 200 PSI. 
Oil pressure gauges found in motorsports were, at one time almost exclusively mechanical. They were the darlings of the racing community. Plumbing was always pain, simply because the plastic lines most were fitted with could prove down right 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). 
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, only then 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 black 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). 
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.