| Author |
Message |
Kevin Marcus (Rumordude)
Junior Member
Username: Rumordude
Post Number: 83
Registered: 9-2001
| | Posted on Tuesday, October 29, 2002 - 9:16 am: | |
I have a gtech pro and it is pretty neato, especially at the track or at a nice onramp. but i would only get one if you do a lot of tuning of sorts or have a lot of different cars to play with. |
James Selevan (Jselevan)
Junior Member
Username: Jselevan
Post Number: 189
Registered: 6-2002
| | Posted on Tuesday, October 29, 2002 - 12:44 am: | |
Hans - your are correct in citing Newton's equation F=ma, but it is a little more complicated than that. Power is measured in Watts, or Newton-meters per second. Force is measured in Newtons. Thus, one must normalize to time to arrive at force.
1 horsepower = .746 kiloWatts. Thus, if all we know is acceleration (sensed by the accelerometer) and mass, then we obtain Newtons. Newtons must now be converted to horsepower by dividing by time (to arrive at speed - distance over time). I assume the time is that measured between samples of acceleration.
This site helps explains things. http://www.howstuffworks.com/fpte5.htm
Jim S. |
Jeffrey Caspar (Jcaspar1)
New member
Username: Jcaspar1
Post Number: 37
Registered: 5-2002
| | Posted on Monday, October 28, 2002 - 11:44 pm: | |
I have one of the original units and have used it at the dragstrip. The 1/4 mile ET is pretty accurate. The MPH reads actual MPH where the track averages over the 20' so the G-Tech would read 123 where the track said 118. I find it hard to use on the street as you need a completely flat , straight strech of road where you can run.
The HP number was very close: It showed me 414RWHP which correlates pretty well with my previous dyno results of 422 RWHP SAE. The only information you need to enter is the vehicle weight. It gets no info from the cigarette lighter other than power. It measures your maximum acceleration rate and uses this to estimate HP. Similar to formulas such as this: http://www.prestage.com/carmath/calc_HP_fromETandWeight.asp
Fun, but not a must have. |
BretM (Bretm)
Advanced Member
Username: Bretm
Post Number: 2811
Registered: 2-2001
| | Posted on Monday, October 28, 2002 - 8:33 pm: | |
Wouldn't gearing affect it. I could have a 1000hp engine with a 2:1 first gear and 3.0 rear that would take an aweful long time to get up to high rpms and hence speed, at the same time I could have a 100HP engine with a 4:1 first and a 4.88 rear that would wind up and accelerate faster than hell. Plus what happens when you can't engage that 1000hp engine with those gear ratios without ripping apart the clutch, so you side step it and get wicked wheel spin. I still find this HP measuring to be a little iffy. Granted I have exaggerated here, but the difference between the stock 4.06 rear in the US 8 QV and swapping it to a 4.88 would certainly make it accelerate quicker. I'm under the impression that nothing has to be entered, but it would seem to me you'd need first gear ratio, second gear ratio, weight, rear end ratio, tire diameter, and 0 wheelspin (could be accomplished by not starting from a standstill presumably). In their ad it says that it gets all the information it needs from the cigarette lighter, lol. |
Hans E. Hansen (4re_gt4)
Member
Username: 4re_gt4
Post Number: 343
Registered: 4-2002
| | Posted on Monday, October 28, 2002 - 7:27 pm: | |
The HP measurement is a very simple calculation needing only one more input: weight (or more technically - mass) To accelerate a given mass at a certain rate needs a specific amount of HP. Basic junior high physics. The only fly in the ointment is frictional losses, in particular aerodynamic. As speed increases, more HP is used just pushing the car against the wind and not used for acceleration - which the G-Tech measures. Frictional losses tend to be relatively constant, although they do also increase somewhat with speed. So, although HP can be calculated with this device, it is not the total wheel HP as would be measured with a chassis dyno. |
BretM (Bretm)
Advanced Member
Username: Bretm
Post Number: 2807
Registered: 2-2001
| | Posted on Monday, October 28, 2002 - 6:52 pm: | |
I can see how it can measure g forces and therefore acceleration, etc but how does the new one measure HP? I seem to remember seeing an ad that claimed this, it seems to me that you would have to enter quite a bit of information for this thing to turn it into HP numbers, and even then I can't see it being really that accurate. I have every once in awhile thought about getting one, but I think the borrowing idea might be better, although it might be cool to have. |
David Jones (Dave)
Member
Username: Dave
Post Number: 390
Registered: 4-2001
| | Posted on Monday, October 28, 2002 - 6:33 pm: | |
I have a G-Tech pro, but the last time I used it, it laughed at me and told me my car was slow, so I put it in the corner of the garage with all the other useless crap I have purchased over the years that I don't use any more. |
Aaron Williams (Aawil)
New member
Username: Aawil
Post Number: 13
Registered: 8-2002
| | Posted on Monday, October 28, 2002 - 3:20 pm: | |
I had a g-tech pro for a while but found the leveling annoying so I sold it and got the tazzo.
It mounts sturdy and has dual accelorometers so there's no leveling. The competition g-tech looks interesting but I don't use it often enough to justify the cost. Here's the tazzo site....
www.tazzo.com
|
Randy (Schatten)
Member
Username: Schatten
Post Number: 435
Registered: 4-2001
| | Posted on Monday, October 28, 2002 - 2:59 pm: | |
original unit - yes. I borrowed one from a friend for a while. Fun for a few jolts of accelleration off the line. Accurate - quite so. I'm curious to see the GTECH Competition unit.
Worth the money? Not really. I'd recommend borrowing one from someone for a week and that's probably all you want, unless you are doing modifications to a particular car that you want to test for drag racing/g-loads on a normal basis. |
Lou B (Toby91)
Junior Member
Username: Toby91
Post Number: 93
Registered: 4-2001
| | Posted on Monday, October 28, 2002 - 12:23 pm: | |
Any experience with the original unit or the latest "Competition" unit? Worth the bucks? |