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On 20 Nov 2004 at 9:06, Toby Erkson wrote: > > Jim Adney wrote: > > >On 19 Nov 2004 at 17:13, Toby Erkson wrote: > >>Jim Adney wrote: > >Most of this sounds fine. I'd want to know more about the G-Tech just to know > >how sensitive it is to interpretation. Does it record a digitized record of the > >run so that you're not left to choose a max meter position? If so, one thing > >that might be wrong about this would be the fact that the test was not "Blind." > >Not being blind makes any test more likely to turn out the way the tester wants > >it to. > > > >Another might be the fact that this car was rather new to you, and the > >synthetic runs were done after you had some practice. Most people will show > >some improvement with practice at things like this, especially if they get to > >look at the results each time. > Good point. However, I was doing 0-60 testing before the hp testing and > had practiced 1/4-mile launches so I was already familiar with the car. > A slight burn-out gave me the best launch and lowest 1/4-mile time. For > the hp testing this isn't required, you just gotta get moving. Having some practice ahead of this testing certainly makes the results more reliable. The lack of a blind, or double blind, test, remains a problem, but this is a problem to do well. > >How do you get from acceleration to HP? > Hey, I'm not the one working in the physics dept! :-) Here's the > product listing from their web site, my unit is the GTechPro which is no > longer available: http://www.gtechpro.com/prod.html > Here is the location for the user guides. To see mine, click on the > "U.S. mode user guide" at the very bottom "Gtech Pro User Guides". It > even includes accuracy ;-) http://www.gtechprosupport.com/support/ There should be a number of ways to approach it, but the manual doesn't spell out their method. They ask you to input the car's weight. They state that they integrate the acceleration [twice] to get distance, so I would guess that they integrate it once to get speed. Once they get speed as a function of time, it's fairly simple to derive HP, but integrating magnifies errors in the original acceleration data. It seems odd that they give the accuracy of the HP measurement as 3 HP, while the acceleration error is only .02 G. Did the final numbers come out in any particular agreement with the Jetta's published HP? Even though the absolute numbers might be off, taking a difference measurement, like you did, should be more reliable. All in all, it looks like a pretty interesting instrument. Did you bring it with you to Parma? -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~