Performance at high altitude

[humfrz]

Originally Posted by funwheeldrive

I was under the impression that turbocharged cars have notably less power loss at high altitudes in relation to NA?

At the same boost, the difference may proportional (relatively speaking).




humfrz

[Allch Chcar]

The air resistance is lower so it's not as bad. Plus it lowers the needed octane in fuel. Fill up with 91 in the flatlands and you'll be running closer to what you would if you had 93. I've driven mine over 5k feet elevation and still had plenty of power.

[humfrz]

Originally Posted by Allch Chcar

The air resistance is lower so it's not as bad. Plus it lowers the needed octane in fuel. Fill up with 91 in the flatlands and you'll be running closer to what you would if you had 93. I've driven mine over 5k feet elevation and still had plenty of power.

Oh, ....... I don't believe that the difference in air density, is going to make a significant difference in air resistance ....... at the speeds you would travel at, driving at the higher altitudes ........


humfrz

[Ganthrithor]

https://en.wikipedia.org/wiki/Density_altitude

Increased temperature and decreased atmospheric pressure (as well as increased humidity, although it has a ~much~ smaller effect than the other two) both decrease engine performance. Unless you've got an engine that has arbitrary power limitations at lower altitudes (you don't), you're going to see significant power losses are you increase your operating density altitude.

Atmospheric pressure decreases with increasing altitude. It also varies with the weather (this is what you're hearing about when you hear people mention barometric pressure changes or high- or low-pressure weather systems coming into your area). More pressure = happier engine.

Temperature has a huge impact on engine performance because it affects the density of air. Hotter air = less dense. Colder air = more dense = happy engine.

Imagine one of your cylinders being like a soda bottle. If you fill that bottle with dense air (like you'd find at low altitude on a cold day) lets say you've put 100 air molecules into it (obviously this is a gross exaggeration as literally several more air molecules than that will fit in a bottle, but hey). If you fill that same bottle with air up on some 7000' mountain peak on a summer day when it's 95F out, that bottle might instead contain 70 molecules of air, because air molecules at that altitude are more spread out. Sadly for you, your cylinder volumes are fixed, so fewer air molecules per unit of volume = fewer air molecules going into your cylinders. Each bit of fuel you put into your engine requires a bit of air to mix with it so it can burn properly (again not accurate numbers, but bear with us), and if there are fewer air bits, you can't efficiently burn as much fuel. The electronics will automatically squirt less fuel into the cylinders to compensate for the reduction in available air (so the mix of fuel and air stays efficient), but less burning stuff = less shoving of pistons = less power.

Lower air density also has a negative impact on engine cooling, since less dense air is not as effective at removing heat than dense air. Operating temperatures tend to increase as the air gets less dense, which I assume in modern cars means they probably have to de-tune the engine more for adequate knock-protection.

Basically your engine performance is gonna get fucked from every angle. Even turbocharged cars lose significant chunks of performance at high altitude. I can tell you from experience that the 86 feels noticeably slower up at 12,000', even on a cold day. Up at 14,000', even my turbocharged GTI was super sluggish. I drove my BRZ at or above 5,000' (most of the fun driving was at 7-10k) for the first few months I owned it and it felt noticeably punchier down at sea level when I moved. When I go back up to 6,000' on weekend drives here in SoCal, the car always feels slow on uphill bits at high altitude.

You could add FI to increase power and make the car feel as powerful --or more-- than a stock car would down at sea level on a standard day. Just don't forget to find a way to keep it all cool somehow.

[Allch Chcar]

Originally Posted by humfrz

Oh, ....... I don't believe that the difference in air density, is going to make a significant difference in air resistance ....... at the speeds you would travel at, driving at the higher altitudes ........


humfrz

At the speeds I drive it does.

[humfrz]

Originally Posted by Allch Chcar

At the speeds I drive it does.

...... ol Allch Chcar ....... driving at altitude .........

humfrz

[Allch Chcar]

Originally Posted by humfrz

...... ol Allch Chcar ....... driving at altitude .........

humfrz

A BRZ will fly given the right conditions.

[humfrz]

Originally Posted by Allch Chcar

A BRZ will fly given the right conditions.

Well, your BRZ might fly ........ but, I couldn't get my FR-S to lift off.....

(maybe I needed a bigger wing .....??)


humfrz

[Tcoat]

Originally Posted by humfrz

Well, your BRZ might fly ........ but, I couldn't get my FR-S to lift off.....

(maybe I needed a bigger wing .....??)


humfrz

[Spuds]

Originally Posted by funwheeldrive

I was under the impression that turbocharged cars have notably less power loss at high altitudes in relation to NA?

A turbo system is usually artificially limited to a specific pressure after the compressor. While there is a physical maximum pressure difference between ambient and manifold pressures for any given setup you don't reach that until very high altitudes. At a high altitudes, all the compressor has to do is spin faster to make the same boost.

Turbochargers were originally developed to allow WW2-era aircraft to perform better at altitude.

[Spuds]

Originally Posted by Tcoat

Technically falling with style, but I'll let it slide...

[Teseo]

Originally Posted by Spuds

Technically falling with style, but I'll let it slide...

Buzz lightyear, damn im getting old