Gtech Pro

[HUMMERcustoms.com/TAZ]

I got a Gtech Pro last fall and have not messed with it yet. How acurate is this system for 0 to 60, 1/4 mile, HP to wheels and torque? It is supposed to give You that and more stuff. I'm about to give up on dyno. I watched a Car and Driver weekend before last, I think it was and they used one to test 5 muscle cars for all these things but they did not mention how it compared to say track time or dyno. They were using it to compare the 5 cars so there must be some amount of quality to it's numbers. Has anyone had much experience with one? Let me know what You think and any tricks You may have that made it more accurate or easier to use properly for more acurate numbers.
I'm ready to put it up and just go with those numbers if they are any good. I had planned on using it but after a dyno to see how it coompared.
Thanks
TAZ

[HUMMERcustoms.com/TAZ]

I got a Gtech Pro last fall and have not messed with it yet. How acurate is this system for 0 to 60, 1/4 mile, HP to wheels and torque? It is supposed to give You that and more stuff. I'm about to give up on dyno. I watched a Car and Driver weekend before last, I think it was and they used one to test 5 muscle cars for all these things but they did not mention how it compared to say track time or dyno. They were using it to compare the 5 cars so there must be some amount of quality to it's numbers. Has anyone had much experience with one? Let me know what You think and any tricks You may have that made it more accurate or easier to use properly for more acurate numbers.
I'm ready to put it up and just go with those numbers if they are any good. I had planned on using it but after a dyno to see how it coompared.
Thanks
TAZ

[KenP]

I hope this helps.
From their website:
http://www.gtechprosupport.com/support/FAQComp.htm
Q: How accurate is the Gtech?

The Gtech Pro Competition is extremely accurate and repeatable. We routinely take 12 new Gtechs at random and subject them to testing in a controlled environment that eliminates variables such as pitch, mounting system problems, etc. Typically, all 12 Gtechs measure the same 1/4 mile time for a 1-g run, plus or minus five thousandths of a second.

For horsepower measurements, we have observed accuracy and repeatability in the range of 1-3 percent.

The accuracy and repeatability of your results can be influenced by many factors, such as vehicle pitch, road surface, environment, mounting system, driving style, etc.

Q: The HP result from my Gtech is different from the results from my local rear wheel dyno - why?

The Gtech usually gives HP values which are lower than a traditional dyno. Lower figures are due to aerodynamic losses incurred during driving, and increased rolling resistance of the tires on a real road surface as opposed to a smooth dyno drum. In any case, the power measured by the Gtech is truly the amount of power left to propel your car forward, which is really what matters when tuning a winning vehicle.

Q: Why does my dyno plot look "flatter" than the dyno plot I've seen from chassis dynos for my car?

This is primarily due to aerodynamic drag on your vehicle. The amount of horsepower that is spent overcoming aerodynamic drag is proportional to the cube of the vehicle velocity. In other words, you use 8 times as much horsepower just to overcome aerodynamic drag when your velocity doubles. For example, if aerodynamic drag robs your vehicle of 3 HP at 25 MPH, it will be robbed of 24 HP at 50 MPH... the velocity doubles, but the aero drag loss goes up by a factor of 8!

So even though you are usually generating more horsepower at higher RPMs in a particular gear, you are also going faster, and the horsepower needed to overcome aerodynamic drag is much higher at the upper end of the RPM range. This increasing "negative horsepower" due to aero drag is largely cancelling out the increased horsepower generated by the engine.

You can use this page to calculate the horsepower that is robbed due to aerodynamic drag.

Q: What is the difference between the HP measured by the Gtech, and the HP measured at a dyno, and the HP given in publications?

First of all, there are variances even between dynos. That is to say, if you take your car to 5 different dynos, you will probably get 5 different results. None of them are “wrong”, it’s just that they all measure in a slightly different way, under slightly different conditions. As any experienced tuner will tell you, when you are tuning/modifying your vehicle, you should always go back to the same dyno for comparison.

Most publications list the “crank horsepower”, which is the horsepower put out at the crankshaft, with no transmission, etc... connected to the crankshaft.

Most dynos measure “wheel horsepower”, which is the power delivered through the wheels (front, rear or all wheels); this power is what accelerates the vehicle forward. Consider all the mechanical components between the engine crankshaft and the wheels, as well as the friction (rolling resistance) between the rubber tires and the surface of the dyno roller, and it is no surprise that dynos measure a lower HP figure (after all, they are measuring power at a different place.) Some dynos have “tweaks” and adjustments that raise the measured wheel HP figure based on a number of factors, bringing the delivered number more in line with the manufacturer’s crank HP figure.

As for the Gtech, it will read even lower than a dyno, because of additional sources of power loss that affect a moving vehicle. One of the largest culprits is aerodynamic drag. Some other factors include road surface irregularities, environmental conditions such as wind and humidity, etc...

[HUMMERcustoms.com/TAZ]

Thanks Ken
Big help!!
TAZ