Weather and HP :)

[duhawks]

Yeah when I had my headers done I couldnt really feel all that much power but when I got over a 100 mph DAMN!!!! I would run even with cars to about 110 mph and then I would start pulling like I shot it with some NOS.

[rocket5979]

Originally Posted by duhawks

Just checking on everyone over here I have been busy doing some mods to the R8 but my vbox data is all over the board because of the weather here lately. I started doing some digging and thought I would share this with everyone.

Check this link out. I just get all the variables off the weather channel and input them. It will give you relative hp to the current conditions. This is what the dynos use for the SAE correction factor too.

I was un happy with an exhaust install and retune of my car even though my vbox data was a fraction better but more inconsistent. Well I started doing some reseach on weather and engines. Turns out I was losing almost 8% hp due to the hot weather, moisture in the air and the pressure.


Engine Tuning Calculator - using dew point


Hope everyone is doing well. I do miss my m6 The sound of the RPi exhaust was just heaven.

It is called a Density Altitude calculation. The initial reason how the formula came to be is that airplane pilots of long ago realized that for some reason their planes seemed to lose power the higher they went and on real rainy and hot days. This of course was due to the oxygen content being lower by percentage in a given volume of air ingested. Actual elevation, Air Temp, Barometric Pressure, and Humidity (dew point) all affect this.

The SAE correction for dyno's use a standard of a 77°F (25°C) day with 0% humidity and a barometric pressure of 29.234 in-Hg (99 KPa) at sea level elevation as a baseline. If you dyno your engine with higher temps, higher than 0% humidity, lower barometric pressure, or at a higher actual elevation then your power will be reduced below the SAE standard due to environmental conditions and a correction factor % will have to be added. Inversely, the same will go if you encounter conditions on the opposite side of the baseline since then you would have to subtract the % of correction.

These correction factors are used with dyno's and also with 1/4 mile dragstrip times as well.

There is one item which the dyno SAE, STD, DIN, or other correction factors cannot account for. That is spark timing retardation due to knock, which is in turn due to high combustion temps, which are affected by intake air temps. Some vehicles are tuned more closely to the edge of knock so that when they encounter higher temperatures their ECM pulls spark timing which lowers power. Other vehicles aren't tuned as close to that threshold of knock and may not pull as much or even any spark timing when encountering those same hot conditions. So that will be an X factor that the correction factors will never be able to account for since things are different from car to car and day to day. I would advise that you try to do your vbox pulls on days with similar temperatures. Just something to take into account to keep variables to an absolute minimum if you are planning on getting repeatable data.