Tazicon

iTrader: (1)

So I had the car in a place that is a mile high, and I was shocked how much performance I lost. I knew altitude affected cars but I thought on newer cars the computer compensated fairly well for the lack of air. I guess thats why my friends who live at 5,000' go with Turbos and Superchargers. Anyone else notice this? It was a pretty drastic change.

anomalocaris

Simple physics. One formula for calculating power loss at altitude is:

(elevation x 0.03 x hp@sea level)/1000

For the G37/IPL at 5280 feet the approximate loss is 55 horsepower. Yes, you'd notice that.

BTW all engines lose power at altitude, even FI cars. It's all about the available oxygen...



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tejasg37x

Try driving at 9,000 ft and see how it is...I did that last week.

JSolo

iTrader: (14)

Years ago, I drove (the camaro) from chicago to phoenix. I remember going through denver and other areas in co. In order to keep the car at 55 mph, I had to be at ~3K-3500 rpm in 4th gear. Now keep in mind, near sea level, the car easily did 80 in 6th gear at 1800 rpm (5.7L v8). On the otoh, when I was down south last summer near the smokies, I had no trouble keeping the bike (09 fz1, with intake/exhaust mods) at 60-70 at normal engine speeds. The power/weight ratio comes in play big time at higher elevations.

TVPostSound

iTrader: (9)

Yes, they compensate for the lack of air/oxygen by leaning the fuel to match the magic 14.7:1 ratio. Not for power.

Less air and fuel = Less power.

Legz

iTrader: (1)

@ 4300 ft alti, 0-60 measured at 6.2sec w/ gtech, vs 5.2 of motortrends

anomalocaris

Using the NHRA's altrude correction factor, you multiply your ET at sea level by 1.063 to see how you'd run at Denver. So an ET of 13.5 at sea level becomes a 14.4 in Denver.




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trcb777

All engines lose power as altitude increases but in a N/A engine the effects will be much more. The percentage of oxygen, nitrogen, carbon dioxide or other gasses that makes up air is the same at any altitude. The pressure is getting less and less the higher you go up. If you can increase that pressure with a turbo you will not lose performance nearly as fast as you would in a n/a engine. I've flown single engine n/a airplanes and turbo airplanes, the turbo aircraft have a much higher service ceiling.




BTW all engines lose power at altitude, even FI cars. It's all about the available oxygen...



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anomalocaris

FI engines lose about half the power that a NA engine does at altitude. Again, NHRA correction tables say to use half the NA correction factor for FI engines.

It is not the percentage of oxygen in the air that matters, rather it is the mass of available oxygen, which is less the higher you go, less the hotter it is, and less the higher the humidity is. A really really hot, wet day at sea level can be as bad as thousands of feet of altitude.


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trcb777

which is called density altitude. A hot, humid summer day in Florida at sea level could have a density altitude of 2000 ft above sea level. So the engine performs like its at 2000 ft. Not really a problem in a car but could be a problem for takeoff performance in a airplane. Now it really could be a problem on a hot, humid day in Denver. Thats why Denver's runways are like 3 miles long.