Have you ever wondered how your car matches up to cars in the magazines? A'PEX makes it possible to find out with its new third generation Rev/Speed Meter (RSM). You can see how your car matches up against some of these insane rides by using the many functions that the RSM offers. These functions make the RSM a great tool for those that do not have access to a chassis dynamometer or live close to a drag strip, because improvements in engine performance can be measured accurately. The RSM uses the vehicle's speed sensor signal, rpm signal, and an optional G-Sensor to measure acceleration times, acceleration forces (measured in Gs), monitor certain engine functions, measure horsepower and what is called loss power (power robbing factors which are a combination of wind resistance, tire friction, drivetrain friction, atmospheric conditions, tire pressure, and engine and drivetrain oil temperatures). Another useful feature that the RSM offers is a speed limiter cut that eliminates speed limiters on many Japanese vehicles. Additionally, the new RSM now utilizes the company's signature blue vacuum fluorescent display to add that show-quality look to your car.
Navigating through the menus is just as simple as A'PEX's other electronic accessories like the Super AFC and the AVC Type-R Boost Controller. One minor change compared to the company's other electronics is a slightly redesigned face with only one switch that act as both a knob and a button. This makes navigation even quicker than before. Its small size (52mm x 126mm x 18mm) allows the unit to mount almost anywhere. In fact, these dimensions make the unit small enough to be mounted below the stereo in many cars. By utilizing an EEPROM, any parameters entered into the RSM will be permanently saved. This way the unit will not lose its memory settings, even if the battery is disconnected. Other very useful features are the outputs for engine rpm and vehicle speed that can activate external relays. For example, a user can trigger his nitrous system at a certain rpm to prevent engine damage and/or at a certain speed to avoid wheel spin. The rpm output can also be used to trigger VTEC solenoids on Honda LS/VTEC conversions.
The acceleration measurements that the RSM can measure are useful for many purposes outside of simply finding out how fast your car is. Other than the obvious purposes of the RSM, a new user-definable Mid Range Acceleration mode can allow the user to measure improvements in engine performance. Although there is a theoretical horsepower calculation on the RSM, the Mid Range Acceleration mode can tell the user what that horsepower can do for the car. The user can define the range of speed beginning and ending anywhere from 0-250 km/h. This allows the user to avoid wheelspin that can occur in lower gears, because test runs can be conducted in third or fourth gear. Improvements can be verified accurately using this method. The Rev/Speed Meter can measure the following: 0-100 km/h acceleration, 0-200 km/h acceleration, 0-300 km/h acceleration, 0-100 meter acceleration, 0-200 meter acceleration, 0-400 meter acceleration, user definable mid-range acceleration (between 0-250 km/h), stop watch measurement (lap/split), horsepower, loss power.
The Rev/Speed Meter can also monitor the following parameters: engine speed (rpm), vehicle speed, travel distance , battery voltage, front/rear acceleration (G), left/right acceleration (G).
Depending on which features the installer chooses to use, there are anywhere from 4 to 6 wires that need to be connected that are all accessible at the car's ECU. If using the optional G-Sensor, the G-Sensor must be mounted to the car and an included wiring harness is plugged into the RSM head unit. Wiring diagrams for Japanese vehicles are included with the RSM, so installation is a snap. It took us less than one hour to complete the installation of the unit into our test car, a 1996 BCNR33 Skyline GT-R. The instruction manuals included with the RSM are very thorough and should be followed step by step to ensure proper operation of the unit.
How does it all work you ask? Before we jump into using the unit, the RSM requires that the user input several parameters before the unit will operate properly. These inputs are the number of cylinders the engine has, the speed signal pulse per revolution, tire size diameter correction, and vehicle curb weight. Tire diameters can be found on tire manufacturer's websites and vehicle curb weights can be found in owner's manuals of cars or manufacturer's websites. If the speed limiter cut, rpm output, and speed output are going to be used then there are additional parameters that must also be input into the unit. With the optional G-Sensor, horsepower and loss power measurements are also available.
The RSM required some initial setup operations that took less than 10 minutes. After the input of these initial settings, we got on the road to put the RSM to the test. Knowing that our BCNR33 Skyline runs 12.40s in the quarter mile at Pomona Raceway and puts 401 hp to the rear wheels on a Dynojet dynamometer, we set out to see how accurate the RSM really is.
As it turns out, using the optional G-Sensor adds considerably more accuracy to the elapsed time measurements the RSM offers. The G-Sensor actually corrects the speed sensor input to compensate for wheelspin and the lack of tractive effort. Without the G-Sensor, the RSM uses only the vehicle speed sensor's inputs to measure distances and speeds and therefore will not account for wheelspin.
The first test was a 0-400 m (1/4 mile) measurement. We set the RSM on the 0-400 m measurement mode and with the touch of a button the RSM's screen displayed "Ready!" The first run yielded a 12.51. After another two passes, the RSM displayed 12.48 and 12.55. One nice feature of the display is that it will retain the best 5 runs in memory for comparison purposes. This shows that the accuracy of the RSM isn't too far off from the clocks at the drag strip.
The next test was measuring horsepower at the wheels. To conduct this measurement, the user must first use the Loss Power mode to determine how much horsepower is lost from factors mentioned earlier. The Loss Power measurement is done through a deceleration process that is explained in the instruction manual. After the Loss Power measurement, then the RSM can properly measure horsepower. You could call the Loss Power measurement a calibration mode for the horsepower measurement mode. Making a pass in fourth gear, the RSM measured 411 horsepower. Not bad for an affordable add-on computer, considering this was exactly 2.4 percent away from the 401 hp that was measured on the Dynojet.
Overall, the A'PEX Rev/Speed Meter is a useful tool. It isn't quite a replacement for a dynamometer or a drag strip, but it can be a useful tool for those that want to find out what their car can do, or for those of you that like to tune your engines yourselves. For only $275 for the RSM head unit, $60 for the G-Sensor, and $15 for an optional head unit mount, the RSM is a good buy. Although the RSM has practical purposes, the new sleek look can even work well as a nice showpiece, or simply just to match your other A'PEX electronics.