Product Analysis and Comments
 
The G-Tech Performance Meter/PRO
$139.95 + S&H
 

This really neat little Gizmo Measures:

This little device is one of the coolest I have seen in some time. Smaller than a radar detector, the Performance Meter/PRO suction cups to the windshield and gets it's power from the cigarette lighter. The device uses a Precision Silicon Capacitive Accelerometer along with some timing circuitry and a display to perform the measurements mentioned above. The User's Manual is easy to read and describes everything you need to know in order to use the unit.

So, if you want to know what your real 0-60 time is, as opposed to whatever Road & Track says it is, this is the gizmo for you. If you want to know your 1/4 mile speed and elapsed time and don't have a drag strip nearby or are intimidated by running with the "big dogs" this may be the answer. If you want to know if the new trick exhaust system or air filter really added 15 HP; this may be the answer. If you don't have access to a chassis dynamometer, this gizmo may be the answer. If you only have $150.00 this IS the answer. All you need is a long straight, flat stretch of road with no traffic or police and a few minutes of time.

Analysis and Comments:

The device is much smaller than I thought, this makes it a bit difficult for me to use, with my big, clumsy hands. A larger, higher resolution display would also be easier to read, especially for the alphabetic characters. The mounting bracket mounts to the windshield via suction cup and anti vibration rubber "feet". The G-Tech then mounts to the bracket with Velcro. I found dis-mounting the unit from the Velcro to be somewhat of a problem because the Velcro is REAL sticky and the unit is very light. It would also have been a great idea if the G-Tech had some NVRAM (non-volatile memory) in it so that the vehicle weight would not have to be entered each time the device power is cycled. For the C5, I found the power cord to be somewhat short - this makes it difficult to get the instrument level since the cord pulls on it. Radio Shack sells an extension cable for $6.99.

Operationally, the device is pretty straightforward - just read the manual. You basically set the mode, enter the weight of the vehicle (if doing HP measurement), ensure the unit is level, then press the button, wait for the display to say "GO" and stomp on the gas. Simple. It is also smart enough to "know" if you are doing 0-60 timing or 1/4 mile timing. But, I found that I had to really slow down quickly after reaching 60 MPH or the unit thought that I was making a 1/4 mile run. After a few attempts, I now know how to do it.
 
 

Technical Stuff and Theory of Operation:

An accelerometer is an electromechanical device that precisely measures acceleration of an object. Acceleration is defined as the rate of change of speed of an object or a ratio of an object's velocity to time. The higher the acceleration, the faster the speed is changing. Starting from zero, if you measure how much your speed has changed over a certain period of time and add it to what your speed was the last time you measured, you will know what your current speed is. You (or Mr. Electronic Circuit) can repeat this for the next time interval and update your speed again, etc. Mathematically, this process is called integration and is the basis of the calculations made by the G-Tech.

The sampling interval is 2.5 ms (400 times per second or 400 Hz). This sampling rate allows for very accurate results. Results can be converted into our units of choice whether it is HP, MPH or "G"-Force (G-Force is the force that results from a change in velocity or a change in direction, it is expressed as a percentage of normal gravity, like .9 or 4 or whatever).

How it works.....

Some formulae:

1. V = A x T Velocity (in feet per second) = Acceleration (in feet per second per second) X Time (in seconds). If you integrate acceleration over time, you will know your velocity at the end of all the time periods. So romp on the gas and the accelerometer can tell you how fast you are going at the end of each sample interval. Now we know how long it has taken us to reach 60 MPH. Once we reach 60 MPH we can stop the car as fast as we want we then will know how long it took to get from 60 MPH back to velocity of zero (braking).

2. D = V x T Distance (in feet) = Velocity (in feet per second) x Time (in seconds). Distance is then measured by integrating velocity (or speed) over time. While we are romping on the gas, we can calculate the distance we have traveled (because we know the velocity from #1 above and how long we have been romping on the gas). Now we know when we have gone 1/4 mile.

Finally,

3. Power is how fast we can deliver energy. Measured by work/time or force x velocity. Common units are the Watt (W = 1 J/s), lb-ft/s, or horsepower (hp = 550 lb-ft/s).

HP = V x A x M Horsepower (in pound-feet per second) = Velocity (in feet per second) x Acceleration (in feet per second per second) x Mass (in pounds). Obviously, all we need to do this is the weight of the object since we have everything else we need from #1 above.  You can get your Corvette weighed at your local landfill or most truck stops.
 
 

Summary:

The results you see for 1/4 mile runs with the G/Tech will be different (usually higher) than at the drag strip due to the fact that drag strip timing calculations are really an average of the speed through a "trap" at the end of the run and the G/Tech speed is the instantaneous speed at the end of the 1/4 mile. Elapsed times should be nearly identical to the drag strip times. All in all, this is probably the best toy I have bought in a while. Ranks right up there with draft beer and sliced bread. For you metric folks, there is a 0-100 KPH version.

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