May seems to be a stupid thing at the first glance, but 2 days ago I was beside the sea. I noticed better overall function of the engine + more horses and vice versa at the 3000 meters above the sea (mountains), and the prove to this word is vacuum gauge reading (20@idle beside the beach and 15 at high altitude)
I figured it as having much more O2 at the sea level and less in high altitude, have you experience this incident by your self?

I have. Think 3k feet is bad? Try 6k+ ft. Try running (physically, not in your car) at a high elevation, and then again at a lower elevation. Easier to breathe at a lower one, right? That's because there IS more O2 at sea level (that's why when ppl climb everest & other high mountains, they take oxygen with them). Same goes for your vehicle. I noticed a BIG difference when I took my 04 silverado from about 6,000 feet down to about 700 feet.
If you pay attention, you'll also notice that gasoline is of a lower octane at a higher elevation.
I was told by someone (can't remember what forum it was though) after I gave them my barometric pressure and a couple other things that I was losing approximately 22.24% hp VS being at sea level (if they did the math right). I've heard that a N/A car would lose anywhere between 15-18% of it's power, and FI cars would lose anywhere between 8-13%.

Can't wait to go back to Ohio, where's there's more oxygen to = more power (for my car AND me) !!!

It's not just more oxygen - it's more air, period. Compression goes up, fuel burns better, yada yada. I just rebuilt a 355 for my '99 Suburban. Home is about 3300 ft and I can pass with ease, most times without dropping out of overdrive. I took it to the Rocky Mountains a couple of weeks ago, it wheezed like an old smoker at 9000+ feet. There just ain't anything to breathe in and compress at that altitude. That's part of why they're going to turbos on the newer 4-cycle snowmobile engines, engines at altitude need help.

BoTy - I've heard that compression drops off about a point at a high elevation (such as 6k feet) before. I still don't understand this...

Mechanical compression doesnt change but cylinder pressure does. If there is less air there to start with, when you compress it to 10:1, it's still going to be less total pressure.
My home track is at 3300ft elevation but because of our weather, the track air can be measure by a combination of air temp, barometric pressure and humidity. Typically we are at 5500ft in the summer

Think of it this way. These #'s are only SWAG's BTW. (scientific wild ass guesses) At sea level there are X # of oxygen molecules per cubic foot, say 100 for a nice round #. These are packed tightly together at sea level. At 6K altitude there might be only 75 molecules per cubic foot of space. They begin to spread out and the density decreases as you go higher in altitude.
For a given compression car at sea level you are getting the full 100 molecules at the max density. At 6K you'll only be getting 75. Thus, theoretically, you'll only get 75% efficiency. That is my oversimplified explanation.

Got it. Thanks for putting it in laymen's terms.

77LT1 is right on the money with his explanation except is not just the oxygen that goes down at higher altitude. All of the different gases that make up the air we breathe become less dense at high altitude.
Oxy is just the only one we care about for the engines.

.All of the different gases that make up the air we breathe become less dense at high altitude.


It's because the higher up you go, the closer to outerspace you are.:cool:

Yeah, and according to Einstein's Theory of Special Relativity, at higher altitude you're actually going faster relative to those at lower altitude due to the increased speed of Earth's rotation. ;)

Actually, this topic really interests me as my Camaro never gets below 6500 ft, so it's really interesting tuning it for the altitude. Keep the ideas and theories coming!

That's part of why they're going to turbos on the newer 4-cycle snowmobile engines, engines at altitude need help.

Thats not entirely true. There aren't any turbos on any OEM mountain sleds. The main reason people put turbos on their mountain sleds is because of the insane power potential. We're talking 350+hp with 30psi boost or more in a 1000cc, 600lb sled. 400hp with nitrous.

OEM's do have turbo sleds but their not on their dedicated mountain sleds that spend most of their time at altitude. That may change in the near future though as turbo 4 strokes are becoming very popular.

3000 meters above the sea (mountains)
Thats a lot of difference in altitude, would feel that for sure, but its just the difference in air density.

Very Nice Ideas, all, But so far I underestand the Fuel Injection Cars and those with high CR (10:1 or so) can run much better then for example (stock 350 smoger)... at 9000 Feet, I lose more than %25 of the power.
And in my opinion, the quality of the engine function at the sea level, can not be obtained with regular tuning (for example carb tuning) at 6000 Feet.
I am still dreaming of the VAC reading I got at the sea level (20 INS/HG) and now it's 16 INS/HG @ 4000 feet

Thats a lot of difference in altitude, would feel that for sure, but its just the difference in air density.

And at the sea level, when the Mechanical CR is for example 8.5:1, you really get that CR but may be it gets 8:1 in 4-5KF :(

interesting thread

just going from ft stockton (2975ft) to san angelo(about 1/2 of that) is about .2-.3 difference in times. and from ft. stockton to houston(about 10ft above sea level) is about .5-.6 difference. like yanking a couple of plug wires. you pick which ones.

can run about 1/2 point more compression here (mabye a tad more) on the pump premium of 91 octane that's available here,, compared to 93 octane in houston. just my experiences.

also,, the more power you make at sea level,, the more power you loose as you go up in altitude.

^^yeah...now imagine the difference I feel going from 6,000 feet to around 700-800ish. :mad:

Oh well, I only have another 11 months in my enlistment in the USAF. I can't WAIT to get back to Ohio!!!

It's funny...when the 267 I had in my camaro was stock (while in Ohio), it felt as strong (maybe more) as it did here in Cheyenne when I had a 4BL and an intake.

Mwilson, I've started threads about elevation changes (maybe not on THIS site) before but they usually don't get alot of responses.

I remember going up into the sierra nevadas and when I got up pretty high I passed 2 or 3 stalled cars. Even the car I was driving (88 5.0 mustang) was acting up a little. It was tuned for sea level operation.

I felt stupid, in 9000 feet since there was no power for the 350 engine to run in 3rd gear and other modern cars were crossing me as if I was driving a 40s car:mad: . Gonna do sth!!! Any solution you guys know?