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I can offer feedback based on tuning 8 to 17 Z cars at a time, in many different locations, with the same type of dyno (Dynojet).
Most locations have been at moderate elevation, and the results have been similar, for similar modifications to the cars. The differences in similar set up's that did occur in moderate locations could be logically traced to differences in compression and cam timing.
The results I found to be out of the normal from group tuning sessions were results in higher elevation locations. The most extreme results were in the highest elevation location, Denver Colorado (OVER 5000 FT).
If you take the corrected power results the dyno offered at face value, you would have to say that Turbo Z cars simply love clean mountain air and they make more power at higher altitude.
Since we know engines make more power with more air, it is more logical to draw a conclusion that the dyno correction software for altitude, at least for forced induction engines, seems to be a little giving.
My *guess* is the Dyno software was written for normally aspirated engines. A NA drops significant power at higher altitude, what the software suggests would make sense for NA’s.
Turbo cars are laggier in high altitude, but the turbo can still produce similar boost pressures, the percentage loss under boost does not seem as significant as the correction software suggests.
Dynojet software allows you to look at a few different industry correction factors, as well as uncorrected numbers. The industry correction factors are supposed to offer similar results in any conditions based on formulas from a given reference condition, the uncorrected numbers are the results in the actual conditions.The STD reference is:
Air Temperature: 60F
Absolute Pressure: 29.92 inches Hg
Relative Humidity: 0% THE SAE reference is:
Air Temperature: 77F
Absolute Pressure: 29.23 inches Hg
Relative Humidity: 0% On a moderate day here in California where our shop is located, the correction factors are close and it is common to see the uncorrected numbers the same as the STD numbers. The SAE number on a moderate day corrects down 1 or 2%. When it is really hot, I have seen the correction factor go up as much as 5% on either STD or SAE, when it is extremely cold out, the STD and SAE numbers correct down from the uncorrected number. In Denver, the correction factors were adding about 10 to 12%.
All the corrected numbers were high compared to tuning similar set ups in other locations that were not at Denver’s altitude.
If I use average numbers that I typically see for set ups tested close to sea level, my best guess is the dyno software is giving about 4 to 5% higher corrected numbers at Denver’s altitude than we typically see for the same set ups near sea level.
The reality is the cars were really making 10 to 12% less uncorrected in the conditions they were tested in. Another interesting tuning trip was Delaware, they have amazing air in that area and it was very cold, the dyno was correcting down, the uncorrected numbers were very high because the conditions were so good.
The cars were really making much higher power than the corrected numbers, racing results from places like English Town prove that those type of conditions do allow engines to produce more power.
For me, a dyno is a tuning tool to allow us to extract the most power from a set up safely. It also allows you to measure gains when testing parts on the same dyno in the same locations.
The correction factors are supposed to allow the same car to show the same result where ever it is tested. In my experience the correction factors are the most skewed in higher altitudes on turbo cars.
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