High Altitude-Effect on Operation

[Spector]

I have always heard that when driving a car at high altitudes there may be a performance difference or some adjustments may be needed to compensate for the altitude, octane of gas etc.

My daughter is driving out to CO to work at a National Park this sumemr with an altitute of 10,000 feet.

Advice, comments. She drives a 4 cyl Ford Zetec engine?
Thanks

 

[DEWFPO]

"I have always heard that when driving a car at high altitudes there may be a performance difference"

There IS a difference, and it is noticeable. There's approx. 3.0 - 3.7% less oxygen (depending on data source)in air for every 1 thousand feet you move up in elevation.

I live in CO at an elevation of 7,200 feet. So all our non turbocharged vehicles put out ~27% less HP and TQ at this altitude. At 10,000 feet it's VERY noticeable.

On the positive side, you get better fuel economy since the ECM leans out the mixture to adjust for the lower air mass.

We still have RU, MU & PU gasoline but they are lower octane since higher altitude requires lower Octane, less air density, less compression, less octane required. (e.g. premium in CO is 91 octane, vs. 93 in 'lower' states.

Your daughter's car will need no adjustments since all important things (fuel mixture, timing) are computer controlled.

If she has never driven in mountain areas, please educate her on the benefit of using lower gears when ascending & (especially) decending steep mountain grades to maintain a safe speed and control without having to ride/burn up the brakes as so many do on the down grades. The shift lever is there to be used, especially in the high country.

The western approach to the Eisenhower Tunnel on I-70 is approx. 6-7 miles of constant 7% grade. It tops out at over 10,000 feet. This puts a strain on the vehicle and the driver to maintain a safe driving position.

Also reinforce the lower power aspect so she doesn't pull into the left lane to pass a truck on the grade in front of a faster moving vehicle thinking she has the power to safely pass when all that happens is she sits there, her car makes more noise, uses more fuel and she's now blocked the left lane and pissed off everyone behind her. People ("flatlanders" I call them) try to do it all the time and create "putz" blocks.

When moving upgrade, momentum is everthing if you don't have an abundance of power, so planning ahead is critical.

Also recommend she NOT use the cruise control in the mountains. She needs to maintain control of her vehicle, not the vehicle control her.

Oh, and RPM is your friend.

Hope this helps.

DEWFPO

[ March 21, 2004, 06:31 PM: Message edited by: DEWFPO ]

 

[TC]

"My daughter is driving out to CO to work at a National Park this summer with an altitute of 10,000 feet...advice, comments."

Absolutely got some advice for her: Enjoy the view -- at 10,000 feet, it's gonna be gorgeous!

DEWFPO got it right -- any newer car with electronic fuel injection is pre-programmed to address everything including altitude, temperature, humidity (I think), etc. You're correct in that the old days, cars with carburetors had jets of various sizes (inside the carb) which worked best in certain size combinations. Drastically changing altitudes (such as driving a "desert" car up into the mountains) put that jet optimization temporarily out-of-whack until a desert altitude was returned to. Same for the car set to "high altitude" carb spec's driven down into the low altitudes. Racers such as myself would often go jet experimenting for other reasons as well.

This has nothing to do with altitudes, but I'd simply suggest that she change any fluids/filters/belts and tunes it up as appropriate before heading off into the woods. The car's "black box" will take care of the altitude.

(I pulled this off the internet): "Holley carbs are calibrated for sea level operation and an inlet air temperature of 70 degrees Fahrenheit. Once you know the correct stock jetting for your particular Holley carb, you can determine whether you live or race at an altitude above sea level. For every 2000 foot increase in altitude, you can reduce the jet size by one size. If you had a carb which has a stock jet size of 80 and you live or race at 2000 feet above sea level, then you would use a #79 Holley jet in the carb. Similarly, a change in the carb's inlet air temperature may require a change in the jet size from the stock calibration. Many racers go a step further by combining all of the weather varibles, temperature, barometric pressure, dewpoint and humidity with the altitude of the track they are racing at to determine the "density altitude". This is a "corrected" altitude above sea level. From there they can determine whether a jet change is necessary to maintain performance or whether to change their "dial in" (if they are bracket drag racers)." http://www.mortec.com/carbtip1.htm

 

[MNgopher]

Excellent summary of High Altitude affects. I was a Colorado resident for five years, and everything is on the money.

One of my favorite stories is when I drove my car out there. We had been cruising along I-80 into Cheyenne, Wyoming (somewhere over 6000 ft) and my car (an 89 Chevy Cavalier with a 95 hp 2.0l 4cyl and a 3-speed automatic) was doing just fine cruising along at 65-70mph (speed limit was 65 then). IF anyone knows what the exit from westbound I-80 to southbound I-25 looks like, its an uphill cloverleaf that leads to a fairly long uphill grade on I-25 to Colorado.

I went up the cloverleaf, and gave her more gas, and more gas, and floored it. My sister looks at me and says - you going to accelerate? TO which I replied, well, its floored! I went up the hill at a screaming 50 mph. Such fun!

After a while, I was able to coax acceptable driving out of the Cavalier, and it really was all about momentum! Long mountain grades were not my friend!

 

[Spector]

Thank you very very much. Very helpful hints and suggestions. Sounds like we need to feed the mice in that 4 cyl well before attacking any hills.

 

[TC]

One more idea...

Since the air is thin at such elevations, the engine will be relatively "starved" for air. Therefore I'd make sure the air filter is relatively clean. If it's perhaps within 10K miles of scheduled replacement, I'd go ahead and change it now.

 

[Asinine]

Also, moltov cotails tossed out the window may not burn as hot as they would at sea level... just in case she was going to do some fire bombing.

 

[TC]

Actually, the air density at 12,500 ft elevation might typically be only 70% of sea level, depending on several variables. Which means you've lost 30% of oxygen for the engine's combustion process...which is why cars move like snails through Sierra Nevada mountain passes...which is why kites won't always fly well at high elevations...which is why aircraft manufacturers detail special "high altitude" take-off procedures...and which is why semi-clogged automotive air filters are a problem in high-altitude Colorado National Parks.

None of which I'd presume someone going by "Asinine" would ever know.

 

[Drew99GT]

Yea, usually for most stock F-bodies/Mustangs V8s for example, they lose around 1 second in the quarter mile at Bandimere In Denver, which is around 5800 feet. Stock C5s are usually running low 14s, high 13s, barely breaking 100 mph in the quarter mile, but at sea level, their in the 12s at 110mph on average, so altitude does play a huge factor in performance. Advice for the Zetec? Well, you could drop in a 302 like Muscle Mustangs and Fast Fords magazine did to a ZX3 Focus

 

[Drew99GT]

Oh, one other thing that non-high altitude residents find out the hard way. There is less air for EVERYTHING, including ambient air to effectively cool the engine. Cars tend to run hotter here in the hot summer time because the density altitude can go past 12,000 feet when actual altitdue is 6,000 feet! So, you've got the pedal to the floor trying to get up a hill because your motor is making only 80% power, which heats the motor up a lot, but there is less air to cool the engine coolent through the radiator. So, keep an eye on those temps when your heading into the hills. May want to do a complete cooling system check for piece of mind and advice her to keep an eye on the temp gauge.