DynoJet vs Mustang
08-15-2003, 10:55 AM
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DynoJet vs Mustang I saw a post here that said the Mustang is an eddy current dyno and the Dynojet is inertial. I asked what an "inertial dyno" was but got no answer.
Eddy current I understand. Torque is measured directly and hp computed from rpm taken from the engine or even the roller if corrected.
I must guess at inertial. I think it means the roller is a large mass that is accelerated by the car. The rpm of the roller is measured and acceleration calculated from the rate of change of the rpm. In other words, rpm is differentiated to get acceleration. This is would explain why you have to heavily filter the results on a Dynojet - digital differentiation is inherently noisy. Then you can compute force from F=MA, and knowing tire size get axle torque. Using rpm gathered as above, you can compute hp. Danged if that isn't the way a G-Tech works, except that they measure acceleration directly and get rpm from noise on the battery voltage.
Based on this, I think I would prefer to dyno on a Mustang.
Comments? What do I misunderstand?
Eddy current I understand. Torque is measured directly and hp computed from rpm taken from the engine or even the roller if corrected.
I must guess at inertial. I think it means the roller is a large mass that is accelerated by the car. The rpm of the roller is measured and acceleration calculated from the rate of change of the rpm. In other words, rpm is differentiated to get acceleration. This is would explain why you have to heavily filter the results on a Dynojet - digital differentiation is inherently noisy. Then you can compute force from F=MA, and knowing tire size get axle torque. Using rpm gathered as above, you can compute hp. Danged if that isn't the way a G-Tech works, except that they measure acceleration directly and get rpm from noise on the battery voltage.
Based on this, I think I would prefer to dyno on a Mustang.
Comments? What do I misunderstand?
08-16-2003, 04:56 AM
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Re: DynoJet vs Mustang Sounds about right to me, but I still wouldn't consider a G-Tech to be as accurate as a Dynojet. A G-Tech can be very picky as far as how it is set up and calibrated from what I've heard. Not only that but I've heard some crazy hp #s when put with mods from G-Techs... some you'd have to wonder if they dumped some nitro in the tank to arrive at their "dyno" numbers. 
08-16-2003, 12:04 PM
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Re: DynoJet vs Mustang
Sounds about right to me, but I still wouldn't consider a G-Tech to be as accurate as a Dynojet. A G-Tech can be very picky as far as how it is set up and calibrated from what I've heard. Not only that but I've heard some crazy hp #s when put with mods from G-Techs... some you'd have to wonder if they dumped some nitro in the tank to arrive at their "dyno" numbers.
In the end, mph at the strip is the real indicator of hp, but, being in the business of data acquisition and analysis (I do the software for a line of instruments used in the steel & iron industries to determine the properties of molten metal) I was a bit taken back when I realized how they (Dynojet) must be doing it. Plenty of room for error, as evidenced by other posts where it showed 25 ftlb high for A4s with one release of the software. But, if the code is correct, it works. I've used the technique with simulations several times.
