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For example, at 85 degrees F, 30.14 Inches Hg (mercury) barometer reading, 40% relative humidity and 5000 feet altitude, the engine only produces about 81.1% of the rated horsepower.
At 8000 ft, your engine has about 2/3 of the power it did at closer to sea level due to the reduced oxygen in the air.
Your car engine is basically a pump that is powered by fuel and air being ignited. With less air/oxygen available at altitude to ignite, your horsepower suffers.
Depending on your gear ratios and speed, you could have manually shifted down to another gear.
This,
Next time try a lower gear... forget over drives. I have also had real good luck with towing switch options engaged climbing through steep hills and mountains. Theses are more offered on truck type vehicles though.
I've driven vehicles at high altitude for over 40 years. The "scratch" calculation is that a non-turbocharged gasoline engine loses about 4% of its power for every 1,000 feet gain in elevation. So, at 10,000 feet (and there are plenty of passes in Colorado that reach or surpass that elevation) you've lost 40% of your engine's power. It comes as a real shock to flatlanders ascending a Colorado mountain pass when their unturbocharged car--even with a V6 or V8--gets unceremoniously passed by one of the latest generation turbodiesel pickups towing a 10,000 pound trailer. At high altitude, turbocharging rules.
Combustion engines lose power at higher altitudes. This is especially true if the engine has no forced induction -- in other words, if it is not turbocharged or supercharged.
Conventional supercharged engines ("conventional" meaning those without variable drive ratios) loose power at altitude at the same rate as normally aspirated engines. This is because they operate at a constant speed relative to engine speed. Since the air going in is compressed by a constant rate relative to engine/supercharger speed, thinner air going in results in a correspondingly lower amount of pressure in the manifold (i.e. boost).
Turbos maintain performance at altitude because turbo speed is not tied to engine speed, but to exhaust flow. The wastegate regulates exhaust flow ergo turbo speed ergo boost. If the air is thinner the wastegate can allow more exhaust gas to pass through the turbo, thereby achieving the same manifold pressure as at sea level. Of course there are limitations. A wastegate cannot divert more than 100% of the exhaust through the turbo. As you continue to ascend higher into thinner, you can eventually reach a point where even 100% of the gas passing through the turbo cannot generate enough compressor speed to compress the thinner air to the same manifold pressure as is achieved at sea level. At that point engine performance starts to drop off the higher you go, just like a normally aspirated engine as it ascends from sea level.
Turbos maintain performance at altitude because turbo speed is not tied to engine speed, but to exhaust flow. The wastegate regulates exhaust flow ergo turbo speed ergo boost. If the air is thinner the wastegate can allow more exhaust gas to pass through the turbo, thereby achieving the same manifold pressure as at sea level. Of course there are limitations. A wastegate cannot divert more than 100% of the exhaust through the turbo. As you continue to ascend higher into thinner, you can eventually reach a point where even 100% of the gas passing through the turbo cannot generate enough compressor speed to compress the thinner air to the same manifold pressure as is achieved at sea level. At that point engine performance starts to drop off the higher you go, just like a normally aspirated engine as it ascends from sea level.
Couple faults in your train of thought.
Engine speed is equal with exhaust flow. RPM's up equal more exhaust. Engine at idle = no boost.
99% of turbocharged vehicles have the compressed air flow thru the carb. There were a few odd turbo conversions in the 70's that the carb was mounted on the inlet side of the turbo.
Modern turbo charged vehicles even have the inner cooler where compressed air is cooled before entering the carb.
Engine speed is equal with exhaust flow. RPM's up equal more exhaust. Engine at idle = no boost.
99% of turbocharged vehicles have the compressed air flow thru the carb. There were a few odd turbo conversions in the 70's that the carb was mounted on the inlet side of the turbo.
Modern turbo charged vehicles even have the inner cooler where compressed air is cooled before entering the carb.
First of all, modern cars don't have carbs any more. They haven't for decades. Second, madpaddy is right -- exhaust flow is not linked to RPMs, or more accurately, they're not directly linked. Exhaust flow is tied to engine load. An engine turning 3,000rpm up a 15% grade is under a lot more load than an engine turning 3,000rpm coming down that same grade. If the engine is turbocharged, the turbo will generate considerable boost going up the hill because of the increased exhaust flow from the engine load; whereas on going down the other side of the hill the manifold pressure will be negative on account of minimal engine load leading to low exhaust flow leading to low compressor RPMs.
I just got back from a trip to Colorado and have a question. While driving west of Colorado Springs my car started losing power. I was going 55 to 60 and ended up barely going 40 to 45. I was at 7000 to 8000 elevation. I turned off the AC thinking that was the problem but no improvement. Had the car checked before and after the trip and the mechanic couldn't find anything wrong with the car.
It was a narrow two lane highway and I was backing up traffic. There were only a few places where I could pull over and let people pass. It was embarassing to say the least. The car is a 4cylinder Chevy Prizm. Usually
I've driven a 8 cylinder in the mountains and never had this problem.
A friend told me I should have downshifted from drive into 2nd but wouldn't that make the car go even slower?
Is there something I could have done differently?
Toyota Corollas (Chevy Prizms) are notoriously bad on hills. They are great cars in relatively flat areas but in the mountains, they are pretty weak.
Engine speed is equal with exhaust flow. RPM's up equal more exhaust. Engine at idle = no boost.
99% of turbocharged vehicles have the compressed air flow thru the carb. There were a few odd turbo conversions in the 70's that the carb was mounted on the inlet side of the turbo.
Modern turbo charged vehicles even have the inner cooler where compressed air is cooled before entering the carb.
Yes, there's a correlation between engine speed and total exhaust flow although it is, as drover mentions, more complex than a direct relationship because of load. Even ignoring load for the moment, however, you've apparently missed the whole point about the wastegate controlling how much of the total engine exhaust gas actually passes through the turbo. At any given rpm, that amount can vary depending on a variety of factors, none the least of which is ambient air density.
At sea level, given a certain engine speed and load, the wastegate may be 50% open to achieve the targeted manifold pressure. At the same engine speed and load, but at 5000 feet of altitude, the wastegate may have to be only 20% open (i.e. 80% of the exhaust gas going through the turbo), driving the compressor faster so that the thinner air can be compressed to the targeted manifold pressure.
A dirty air filter could restrict air flow enough to cause a problem. I had a similar problem with my central and after installing a new filter the power came back to normal.
Even super charged dragsters make less Hp the higher the altitude is. Look at where the records are broken ;mostly at low altitude.With less oxygen means that with same equipped engine it just doesn't make the same HP.
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