Dyno Numbers

[batlbrandon]

I have been debating on whether or not to post this or not because I know someone is going to get all uber butt hurt and cause a flame fest. Then someone else will chime in with some regurgitated "scientific" explanation. But whatever, I gotta get this off my chest.This only pertains to the shops using a DynoJet dyno. I know nothing about the Dyno Dynamics or Mustangs, or (ugh) Dyno Pack.Other than what style they are and that they all claim to be the most accurate.

Dyno numbers, what are you really making. There seems to be some debate about what numbers you get from different shops. First of all setting up your software is the NUMBER 1 most important thing that needs to be done. That means telling your dyno where you are in space. IE: We are at approximately 1050 ft here in Atlanta so keeping your software at 0 altitude or 5280 ft above will drastically alter your numbers. If you are at sea level your number would be lower than here, or if you are in Denver then your number would be higher. Also having the correct ambient air temp is essential. If you're taking air temp from the engine bay or anywhere that is hotter than your actual intake air temp then your whp number will be higher. Barometric pressure and humidity play into this equation as well. It all has to do with air density. The more dense the air is the more power you should be making.

Correction Factor (CF). This is the formula that the software uses to calculate your hp number.
-SAE is the industry standard. This is the CF that DynoJet recommends. This is the formula auto makers use to maintain a standard throughout the world because what a car makes in detroit is not what it makes in Japan. SAE gets called "The old way" but was updated in 2004 to take into account mechanical friction.
-STD is in fact the "old" SAE and does not take into account power loss due to mechanical friction, thus providing a higher end number.
-EEC is a formula they use in Japan and Parts of Europe. Although not at the manufactures. Also yields a higher hp number than SAE.
-DIN is a formula used in Germany, again not by the manufactures. Also yields a higher hp number than SAE.
-Uncorrected is power you are really making on that specific day due to the temperature, humidity and pressure on that day.

Sometimes these numbers vary greatly between CF's. Especially when comparing Uncorrected to the others. Usually (based on our own observations) SAE, EEC, and DIN are all very close. I would say within tenths to 1 hp. The uncorrected numbers do get closer to the corrected based on the Alt, Temp, Humidity, and Baro being close to that which is used in the CF formulas.

There is also the smoothing function which makes your graph lines nice and smooth with the higher the number used. Smoothing at 0 will yield a slightly higher hp number based on spikes in the graph. These spikes are generally small when a good tune has been performed, so if your tune is off then your graph line will be a series of peaks and valleys. It will look like a seismograph rather than a dyno chart! I haven't seen too many shops turn the smoothing down because it basically makes the tune look poor even when it may not be.

Lastly I think that a customer should be there when the final numbers are being put down. I know that schedules conflict and it is not possible all the time to be there when your car is being tuned. But I have seen plenty of cars come through here that had dyno charts claiming one number and then we put it on the dyno and it makes considerably less with no changes being made. This has absolutely nothing to do with the dyno but more the shop operating it. It also has led to the debate about which shop makes more power, or who is the better tuner? If everyone is using the same standard then at least you know that your chart is not being manipulated to benefit the shops image. It does the customer no good to have a fluffed up dyno chart and get spanked by a car with supposedly less or equal power.

Please feel free to comment, or add insight. I will try to respond to intelligent feedback. I am just trying to educate everyone that may not understand what it all means when you get a dyno chart. Or why some people see me ask about this chart or that chart being posted in a non SAE CF.