Pontiac GTO Forum - View Single Post

hsv · 07-20-2008, 09:57 AM

OK, so I've had my Gtech for about a week now, and it is pretty good. Here are my initial impressions.

When you first get it, you calibrate the accelerometer axes by holding it in various orientations (vertical, horizontal, tilt etc.). Then you calibrate RPMs by revving the engine to certain levels (4000 rpm, 3000 rpm). It asks for vehicle weight, and number of cylinders. Once you've done that, you are ready to go.

The person who sold it to me on ebay neglected to tell me that the cigarette adapter was broken (the wiring in the adapter plug was broken -- had to pull out the ohmmeter to figure this out). Fortunately, was able to get a new adapter from RadioShack for $10 (so $185 all up).

There are two modes of operation: drag mode and race mode. Drag mode measures 0-60', 1/8 mile, 1/4 mile, 0-60 mph, trap speed, and hp/tq curves (showing gear changes). It's very useful. In race mode, you see lateral and longitudinal acceleration (instantaneous) and you can log up to ~2 hours (at 10 Hz sampling). You can then feed that into the road racing software which plots these out for you in real time (along with engine RPM), and then maps your acceleration to a g-force circle (maps your lat/long acceleration into a circle) which allows you to see how close to the limit you are driving (the closer the better for racing).

Overall, the unit works well. There are a few glitches though. The biggest one is that the longitudinal acceleration is *very* sensitive to the position of the g-tech (angle). Generally you can calibrate it so that it is close to 0 at rest, but sometimes it's not that easy. The RPM feature is pretty neat, but can sometimes have some noise at low RPMs (or changing down) it can spike up to a few k RPMs before settling back to 800 or so (not too bad). The acceleration display is not so great (it shows instantaneous and the maximum over the last minute or so -- it might be a moving average). I've seen other units that show a graph v. time. This is a much nicer way to do it.

The unit also has shift lights, which are very useful. It's much easier to see the red flash out of the corner of your eye than having to look down at the tach.

I bought the unit mainly for the logging feature. I'm going to go SCCA solo-ing and wanted to be able to analyze my runs to see where I can improve. The unit is great for this. Drag mode is really good. It's nice to know how fast you are accelerating and also to see the engine "dyno" curves. I imagine that will come in useful if I ever decide to tune the engine myself (along with an OBDII scanner).

Physically, the unit was a lot smaller and lighter than I had expected (it didn't *feel* like $300). So that is about it.

One word of caution though... My first time out with it, I got pulled over (first time ever!). I was spending too much time looking at the unit rather than concentrating on what was around/behind me. I was on a straight four lane (2 each way) and was sprung doing 59 in a 40 zone. To make matters worse, my inspection sticker had expired. So there I am, sitting in the car, with my brand new Gtech-pro flashing away, with the officer telling me all of this. I knew I was gone, and resigned to getting a ticket. So the officer comes back and says to me: "I'm going to give you the break of the century..." and just gives me a warning. I think she couldn't believe she was doing it either...

Cheers,

HSV.