If you're into modifying your car, you quickly find that assessing performance changes by "feel" is fraught with difficulty. A car which is made louder (by a change of exhaust, for example) always feels faster - even when it isn't! And if you've just spent a heap of time and dollars on a series of mods, it's very natural to be sure that your car is much quicker than it was before you started your "improvements"!
Measuring 0-100km/h times against a hand-held stop watch is (with practice) much more repeatable than you'd first think, but it's still not the best way of doing it. Using a properly timed dragstrip gives great accuracy - but it's a bit hard to go to the drags frequently and cheaply.
That's where the G-Tech Pro comes in. A tiny device (only 70 x 55 x 15mm), it simply sticks to the inside of the windscreen with a suction cap, gets a power feed from the cigarette lighter, and reads off performance times! It can also be used to estimate the peak power available at the wheels, measure positive and negative acceleration, and more.
It's available from many auto accessory stores, or direct from Tesla Electronics at www.gtechpro.com The price from Tesla Electronics is US$139.95, with prices in Australia close to A$350.
How it Works
Inside the G-Tech Pro is an electronic G-sensor (accelerometer) which can detect how much acceleration the car is undergoing. To work out performance, the instrument splits up the acceleration run into many tiny time "slices". It looks at how hard the car is accelerating during each time slice, and therefore knows how far the car must have travelled during that time period. From the acceleration figures it also knows how fast the car must be going, and so the time taken to reach a certain speed (eg 100 km/h) or cover a certain distance (eg 400 metres) can be calculated.
In calculating how much power is available at the wheels, the G-Tech Pro uses the formula that power is speed x acceleration x car mass.
But you don't need to know any of this to actually use the G-Tech Pro - all of the calculations occur inside the device.
Measuring Performance
The most common use for the G-Tech Pro is likely to be in measuring 0-100 km/h (or 0-60 mph in the Imperial version) and standing 400 metre (quarter mile) times. The set-up procedure is the same to measure either of these.
The G-Tech Pro is attached to the inside of the windscreen and the device is levelled. When the car is stationary and is positioned on a flat surface, the instrument reads off any instrument inclination as a G reading. This makes it easy to see when the G-Tech Pro is actually level. However, levelling the instrument is a fiddly operation because the mount is a bit stiff and unyielding. When pushed, it tends to jump too far, meaning that the device is often then tilted too far the other way!
After the G-Tech Pro is levelled, "acceleration" mode is selected, and then the switch is set to the middle position. Just before the timing run starts, the switch is pushed, and there is short pause before the display flashes -Go-. You don't have to leave at the exact moment the display tells you to - the device only starts timing when it senses that you've launched.
If you want a 100 km/h time, start to brake after you've passed 100. The display shows your 0-100 time and then also shows your 100-0 braking distance. If you keep on accelerating after 100 has been reached, the G-Tech Pro automatically knows that you want the 400 metre time. It then shows both the 400 metre time and the speed reached at the end of the 400 metres.
In practice both of these measurements are easy to make. While the handbook looks slightly involved as it describes the techniques to use, in real life they're pretty easy. For the 0-100 time we found that the G-Tech Pro was consistent and certainly accurate enough to measure slight performance changes. Over the 400 metre distance, the times were accurate but the trap speed was a little high when compared with a dragstrip. This is to be expected, because drag strip timing averages the speed over the last 20 metres or so, while the G-Tech Pro gives the speed at the end of 400 metres.
Measuring Power
To measure power at the wheels, the G-Tech Pro requires an accurate vehicle mass figure. The handbook suggests that the nominal vehicle mass (as on the vehicle plate) is a fine figure to use - just add 85kg for each person! We would suggest that it is a far better proposition if the car is weighed (complete with driver) on a weighbridge.
The mass of the car is inputted into the G-Tech Pro by tilting the instrument while watching the display count upwards. The count can be slowed by tilting the device at a shallower angle, while the number is fixed by levelling the instrument. This approach allows any vehicle mass to be entered.
Once the vehicle mass has been entered, the G-Tech Pro is stuck to the windscreen and levelled. Again -Go- is displayed after certain switches are operated, indicated that you can get on the loud pedal. Note that you don't need to launch hard though, so clutch-saving take-offs can be made. Maximum revs are reached in the first and second gears, and then the display shows the power figure.
But is it accurate? On some cars, yes - and on other cars, not so much! On a Holden Commodore VR V6, the G-Tech Pro figure was very close indeed to the actual power as measured on a chassis dyno. But on a Nissan Skyline GT-R, the G-Tech Pro power figure was 12 per cent optimistic over the dyno reading. However, again the G-Tech Pro was very consistent with this figure, making the accurate measurement of power changes (rather than generating absolute numbers) quite possible.
Other Measurements
The G-Tech Pro can also measure instantaneous G's (such as the peak reached during a launch or under hard braking) and continuous G's. For the G-reading to be considered consistent, the reading must be held for at least 3 seconds. This can be used to measure lateral acceleration, like the sort achieved on a skid-pan. To measure this, the G-Tech Pro has to be mounted on a side window, rather than the windscreen.
Conclusion
Like any other measuring device, the G-Tech Pro needs to be used carefully and with an eye to consistency. Rather than generating unarguable quarter mile or 0-100 times, we see the instrument's primary use being a means of assessing the worth or otherwise of performance modifications. If you keep good records and accurately measure factors such as vehicle mass, we think that the G-Tech Pro is an invaluable tool to have around.
