Maybe if you read all of his first post you would see that g tech isnt the same as a dyno, and really how could it be

They follow the same principle. A dyno measures how fast the wheels can turn a known weight and translates that into HP. The GTech, I would assume, uses an accelerometer to see how fast you accelerate your car, based on its weight.

Like dynos, there are differences between them, such as the difference between Dynojets and Mustang dynos. And the fact that GTech numbers aren't SAE corrected. The readings are off by about 28% to what a normal Tib dyno should be... which is too large of a margin for it to be close. Either the GTech is off horribly with its HP function (Its quarter mile times aren't off by much, +/0.3 sec usually, sometimes better) or the car is f0x0red.

Friend of mine has one... I'll use it after school and see what it gives me. Even if does give bad readings, at least it shows you how the mods are improving your numbers.

why would you think he would need a rebuild, like he said you can only compare a g tech hp rating to another g tech hp rating. You dont really know how accurate it is untill you do it on a dyno and a g tech

Off-topic like hell, but whatever. He even calls them dyno runs in his post... they can't be that far off from actual whp numbers.

Like I said, I'll make a run with one on my car tomorrow to see how it compares on my car to his. I know my car is actually at higher compression than Webtech's standards, and is overall in perfect shape... just flipped 14k miles.

Cool, post them up after you do it im interested as to how they compare.

if the numbers are off by THAT much, you don't really know how the mods are improving your numbers unless you know the comparison between 1 GTech HP and 1 Dyno HP.
is it linear? exponential? until the ratio is certain, knowing that you improved 20 GTech HP is pretty much useless.

Okay, let me clear up the confusion:

Comparing Gtech to Gtech will give you the same gain as comparing the same type dyno to the same type dyno. Just like using different Dynos does you no good. The gtech changes are linear as long as you do them in the same location (no change of grade/slope) and similar conditions (temp/humidty) and you haven't changed anything else on the car.

I did put the explanation in the very first post, but I'll repeat it here to make it clear.

<div class='quotetop'>QUOTE </div><div class='quotemain'>Gtech data:

The gtech is different than a Dyno in that it measure net horsepower rather than wheel horsepower. This means that air resitance (~10hp at 60mph) and rolling resistance/etc (~15hp @ 60mph) are shown in the result (~25hp loss). It's not meaningful to compare gtech numbers to a dyno. It is important to compare them to other gtech numbers.</div>

It's impossible to figure out wheel horsepower with a gtech (though you can do a lot of tests to get close) but comparing gdyno to gdyno is very very useful. In fact you can change the aerodynamics of the car and do two gdynos before and after and see the "net" difference.

The 95ghp (gtech horsepower) + 25hp losses puts gives 120 whp which is right where it should be. After the catback the 101ghp + 25 hp losses is 126whp.


I also ran the gtech in my friend's race prepped Mustang GT. We pulled off the gdyno and he compared it to the dyno he ran on a standard dyno. The gdyno curve followed the dyno curve, same slopes changes, dips and everything (he leans out a bit at 4k) except that it was about 35hp lower across the board.

:blink: Odd... made a run this morning (60ish degrees, slightly humid) and it said 114hp off the GTech. Ahh well, if my car is ~140whp as measured on the standard dyno than I'll take it. tongue.gif

Did you have the correct weight in it? Every 100lbs off reads about 3-4hp diff on the gtech. (I know because I ran my car standard, then again after I put 120lbs of stuff in the trunk) laugh.gif

60F will help a lot too. All my runs were done when it was 85F with about 10% humidity.

Again, the main point of the gtech is to check gains from mods. If you do the run the same way in the same location with the same conditions, it's really quite accurate. Out of the 15 or so dyno runs I've done they vary +/- 1 hp.

The new Gtech are also really really nice in that you don't have to do a 1/4 mile run, just a 2nd gear pull which means you don't have to go above 65ish, rather than 90ish laugh.gif

I used the same weight you did, assuming your not anoemic my times should be right. If I put in more weight than the car actually is/was, than my times would be slower. Ahh well. tongue.gif