my friend got the gtech pro...WAY off to my other numbers...it dynoed me at 307hp and 323 lb/ft of torque, 0-60 was 4.9 and my 1/4 mile was 13.8, my 1/8 mile was 8.8...this all on stock tires...so i dunno, just letting you know

 

Odd, I find the older one to be remarkably accurate. However if you input the wrong weight it will not be accurate.

Sounds like some sort of input/interaction error? Or mabye you got a bad unit?

Wierd indeed...

 

??

 

I thought with the new one all you do is plug in and go, only need weight for H.P. and Tq.

 

you definitely have a fast CL, but probably not THAT fast

 

Gtechs have slight problems with manual cars. They seem to be more accurate with automatics. The up and down motion from shifting skews the results some.
We have found it works best if 2 people help with the correct alignment. One stands in front of the car and can tell if the unit is pointing straight forward. Then do a run each direction and average the 2 runs. Was usually within .05 of the 1/4 mile time when used with an automatic.

 

The error is from the gravity being summed in off the line (due to pitching) and from the tilt from any bumps. The forward acceleration is reduced by the cosine of the pitch angle (the reduction is very small [a typical pitch angle is around 2-3 degrees]) and the forward acceleration is INCREASED by the sine of the pitch angle (some simple trig will suffice). Since gravity is 1 G and forward acceleration is much lower, the unit will "overcompensate" during the portion of the run when the car squats or lifts.

The manual, if "JERKED" hard, will skew the results as you mention. However, the unit works best if it is on dead level ground and the results are not only very similar from run-to-run (with a 0.1- to 0.2 seconds to 60). IMO, if the runs coming and going were quite a bit off when changing directions, it would be a good idea to find a better section of road.

Finally, the clamp could be better on the "GTech Pro" (not to be confused with the newer GTech Comptetion) and any calibration problems resulting from not setting the initial reading to ZERO will result in HUGE errors. If the unit is not clamped well, is being bounced, or isn't being used correctly, it is like letting someone sand the ends of a measuring block or micrometer before use -- it's a tool and can be abused.

Some people manage to get results within a 1/10 second in a quarter mile -- again and again -- and others can't even get it to work period.

If the clamp seems loose or the car has a very hard (or bouncy) suspension on a less than perfect road, it isn't going to be too happy when combined with a poor and/or loose/shaky mount...

 

We do many gauging systems typically with laser displacement or thru-beam sensors and often a line operator will want to compare our automated results with their offline tests typically using a hand micrometer. As you could guess they can come up with just about any number they want. We normally ask to have several other people take the same manual measurement and inevitably we get different numbers from everyone.