I have a gtech, and I've taken it to the 1/4 mile track before to test it's accuracy. It was always within .2 seconds and about 1.5mph of my real timeslip. That was on a prepped flat straight track surface though.

I got similar results to the OP when I used mine on the street in my LT1. I was on a very slight uphill though, and I had a very gentle curve in the road. That throws the gtech off ALOT, since it is an accelerometer.

I have the RR model, and the road race feature is really fun. It measures G's in a turn. I have gotten my camaro up to .85 lateral G's.

 

I've got an old one. If you use it correctly it is pretty accurate, at least with halfway normal car acceleration. The horsepower calculation....not sure how accurate that can be, be to even have a chance it has to be set up just right and with the correct weight of the car.

Of course, as has already been noted, the MPH will be higher than a track number, as the unit calculates speed at the actual 1/4 mile point. Numbers will be closer to that of the testing of the major auto magazines.

 

Popular misconception, fostered by inaccurate statements on the G-Tech website.

The "average" vs actual speed at the finish line does not explain away the typical high MPH errors. The difference between average speed over the last 60-ft, and the actual speed at the finish line is less than 1 MPH for a car pulling 0.20G through the traps - about what our cars can do.

The problem is more likely the result of the sampling frequency being too low in the older G-Techs. The G-Tech only measures time and G's. It arrives at speed by integrating time and G's. Then is has to integrate time and speed to calculate distance travelled. The lower the samply rate and frequency of the calculation, the worse the results.

The OP's 1/8th mile numbers translate roughly to a 14.4-second 1/4-mile at about 97 MPH.

 

Yes, I was referring to a G-tech model that I tried a few years ago. The last time I USED one and compared it to my track times, it wasn't even close. Trap speed was off more than 3 mph. Similar to the OP, my HP was off more than 100 hp, even though I had just measured my rwhp on a Dynojet not more than a month earlier with the same mods.

The problem with a G-tech is that you are relying on an accelerometer than is not connected in any way to your vehicle.

I guess the new SS model is accurate, since it reports 175 HP for the LT1 ???

Dan

 

I own both the "older" and the "newer" style g-tech units.
Have ran them at the 1/4 mile track, on a bolt on 95z.

Both came within 1-3 tenths and 1-2 mph compared to the track readout. Accuracy of the unit has to do with setting the unit up properly: leveling the unit, spring stiffness setting, leveling the unit, approx vehicle weight, setting the rpm, ect.

The 1/8th-1/4 times and mph seem to be more accurate v.s the horsepower/torque measurement, due to the fact that if you spin the tires, it cannot compensate/read this, and your hp/tq readings will be low.

If you have a place that is SAFE!!! to test your ride, and a track is not near, if set up properly the g-tech units are a good measurment and FUN tool.