Drewster67

Come Labor Day Weekend - Im taking the track shark up to St Johns AZ for the 5th Annual St Johns Grand Prix. This will be the first year my shark will taste the track. (other years ran mustangs)

Question: St Johns Elevation sits at 5,736 Ft while Phoenix (Airport) sits around 1,132 Ft.

Do I make any kind of MAF adjustments to compensate for the altitude? Or Just leave it alone and it'll adjust itself?.

TIA

mark kibort

thats its job, mass flow meter! it does it thing on its own, and so does the AFM beautifully. (the afm was tested up to 10,000feet with good accuracy by bosche, yet the EPA wanted even better emissions control, so they added a barometric sensor for fine tuning) less molecules of air that pass over the hot wire, the less its cooled and the fuel is provided proportionately and accordingly.

plan on being down 20% on HP. 60-100mph tests with the holbert cars initial street run over the boarder of nevada and over the sierras, proved to be in the 11 second range. at sacramento, it was near 7 seconds and i was very excited!!!!

MK

Ketchmi

You can figure on about 3.1% of power loss per 1000' of elevation. It really sucks the life right out of a performance (or tow) vehicle. After tuning my 86.5' at this altitude then taking it down to Devek Days a couple of years ago, I didn't want to come back up in altitude. I had traction problems at sea level that I never had up here!

If you are running an adjustable fuel pressure regulator, you might want to pull some fuel out of it. You may hit the bottom of the adjustable range for the MAF and run rich as hell.

Normy

Altitude correction: 1 inch of manifold pressure per thousand feet. Since the atmosphere at sea level on a standard day is 14.7 psi, and this works out to 29.92 inches of mercury....you can say that you lose about 0.5 psi per thousand feet.

I've heard that you lose about 3% horsepower per thousand feet of pressure altitude.

Alas...there are other variables: Temperature plays a big roll as well. There is a thing known as "density altitude". The international standard atmosphere is a scientific definition that means a body of air at 29.92 inches of mercury pressure and 59 degrees fahrenheit. I suspect that "corrected" dyno charts are actually raw data increased or decreased a fixed amount based upon the current density altitude. For example, a 90 degree day in Fort Lauderdale, which is typically 13 feet above the ocean, at 29.92 inches of mercury may correspond to a 59 degree day at 1000 feet above sea level in the standard atmosphere.

I own a special calculator that is built for aviation use, and it has the ability to calculate density altitude. We use density altitude for our performance calculations; we need to know how our aircraft will perform, since it kind of sucks when you run off the end of the runway with passengers on board ...

N!