Originally Posted by jfitzpat

I suspect that my forum days here are now severely numbered. I've been making someone a bit aggravated and I think that my pointing out that he had confused an analog input with an analog output was the final straw.

Originally Posted by jfitzpat

It should be clear by now that I am a huge fan of street/track tuning. But I still think it is important to understand the areas where a dyno is really the right tool.

I think coolguycooz is dead on in mentioning P and T. A dyno has dramatically few variables and is in a better position ot measure the ones remaining. If you look in another thread where I posted two different power calcuations my first point is easy to see. My first calculation is not really all that simple, the 'slope' function called does a spline, but while it can provide a surprisingly close measurement to a dyno - it under reports with a track log. Once the car is moving, aerodynamics have to be accounted for. Again, while the second, much longer, calculation that I provided can produce values quite close to a dyno - there are way more variables involved. Variables that are hard to control and precisely monitor.

Similiarly, getting good results out of DLL or my LogWorks calcuation highlights the second advantage that a dyno generally has. If you are taking RPM from an ECU via MUT, there is rounding (RPM is reported as a value from 0-255). Since the readings are course, the data has to be smoothed to get even a reasonably accurate slope measurement. The way most dynos control load (and monitor RPM) are both more precise, leading to more accurate calculations.

From a tuning perspective it is important to understand that, as much as we want to know an exact HP number - absolute readings are not what is truly important. It is the consistancy and repeatability that is truly important. When you are making tuning tweaks and testing them, you really want to know if the gain or loss of an HP or two is real, or just the side effect of one of the many variables beyond your control.

Again, I am a huge proponent of street/track tuning - I'm just not ready to call dynos obsolete yet!

-jjf

P.S. To Malibu Jake - you'll find some gear calculations similiar to what you are talking about on our forum. There is a user who has been getting some very good results in this area and posting his work.

Regarding taking GPS velocity or other speed inputs for P/T - good luck, but be forewarned that other folks have had some difficulty. It comes down to the courseness issue I mentioned above. A GPS is typically updating somewhere between 1 and 10 Hz (1-4 is typical), and each sample is typically +/- 3 to 10 meters. This makes for an even courser reading than ECU RPM.

P.P.S. I'd love to actually discuss this area in detail. Since I've tried experimenting with low cost accellerometers myself - but I suspect that my forum days here are now severely numbered. I've been making someone a bit aggravated and I think that my pointing out that he had confused an analog input with an analog output was the final straw. Still, feel free to hit me up offline - some of the GPS stuff I've done combines inertial data with GPS data and you might be able to take it a step farther.