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05-24-2000, 10:10 AM | #1 |
Scooby Newbie
Member#: 1528
Join Date: May 2000
Location: Lakewood, CO
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Effects of altitude?
Just a few quick thoughts...
I recently moved from CA (sea level) to Denver (mile high). Here are some questions that have popped into my head... I new to this kind of stuff, so forgive me if these don't make sense. 1. I've heard that each 1,000ft decreases performance by 3%, so 5200'= -15% power? 2. The air is not as dense in altitude, but does the %02 content remain constant? If not, does the car lose more power due to less oxygen or is that what the 02 sensor is supposed to calculate? 3. I recently took a trip up to the mountains (I think I might have been the "highest" RS in the world briefly at 14,000'+) and noticed that the car used less gas. Is that a function of the less dense air? BTW, the car had NO power climbing those high hills! 4. If I go w/ forced induction and tune it to Denver air, do I have to worry when I drive the car to lower altitudes? Thanks for any light you guys can shed on these Q's. Stephen
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05-24-2000, 01:03 PM | #2 |
Scooby Guru
Member#: 935
Join Date: Feb 2000
Chapter/Region:
MWSOC
Location: ಠ_ಠ Chicago
Vehicle:Will Woollard Fan Club |
In colorado they also sell lower octane gas. Regular is 85 because of the altitude.
Did you drive up Pikes Peak or Mount Evans? Those are the only fourteeners I know you get to the top of in a Subaru. |
05-24-2000, 01:21 PM | #3 |
Scooby Newbie
Member#: 625
Join Date: Dec 1999
Chapter/Region:
TXIC
Location: Austin, TX
Vehicle:2005 STi WRB/Gold |
Hey Ender, welcome to Colorado. If you are interested, here's the site to get on the Colorado club mailing list. There's lots of events on the calendar there both track days and autocrosses.
http://www.egroups.com/group/SPCR |
05-24-2000, 01:57 PM | #4 |
Scooby Newbie
Member#: 1528
Join Date: May 2000
Location: Lakewood, CO
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Thanks El Kabong. I'm joining the mlist now!
Regarding octane in gas... why would you need lower octane for less dense air? I thought octane is anti-knock rating, which shouldn't be affected by air density? Stephen |
05-24-2000, 02:22 PM | #5 |
Scooby Specialist
Member#: 252
Join Date: Sep 1999
Location: San Antonio, TX
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Ender, I posted on the general topics board that we have an autoX this weekend. If you have time to go down to C. Springs on Sun come meet a few of us!!!
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05-24-2000, 02:49 PM | #6 |
Scooby Newbie
Member#: 1249
Join Date: Apr 2000
Chapter/Region:
MAIC
Location: Chester County, PA
Vehicle:2000 OBS White |
Someone please correct the parts I get wrong. From my very limited understanding and experience:
The Subie's have a knock sensor and something called something like an Automatic Ingition Retard. The gist being that when knocking is sensed, like when climbing a hill, the ignition is retarded to eliminate the knock. This also reduces power, which might be what you are experiencing. My OBS couldn't climb hills worth a darn until I switched from 89 to 93 octane. Not a problem since. Anyhow, might be worth trying higher octane to see if it helps. DuneHopper |
05-24-2000, 09:53 PM | #7 |
Scooby Newbie
Member#: 1528
Join Date: May 2000
Location: Lakewood, CO
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what about the effects of running sc/tc at differing altitudes?
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05-24-2000, 10:31 PM | #8 |
Moderator Member#: 922
Join Date: Feb 2000
Chapter/Region:
MWSOC
Location: Schaumburg, IL
Vehicle:16 WRX (white) 04 FXT (red) |
If you tune it at one altitude it'll either go lean or rich depending on which altitude you go to. Go higher and it'll run richer, go lower and it'll run leaner (and cause detonation, I might add).
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05-24-2000, 11:39 PM | #9 |
over boosted again
Moderator Member#: 1458
Join Date: May 2000
Chapter/Region:
RMIC
Location: Colorado Springs CO USA
Vehicle:2017 WRX Limited 15 Forester XT, 21 Ascent |
Going lower and causing detonation is why the Rimmer S/C is rummored to be 8psi for Colorado and 5.5psi for sea-level. Anyone know if that is true?
Also, I figure a stock RS in Denver/Colorado Springs will do about a 16.8 qtr mile at 80mph, due to the altitude (using NHRA adjustment tables). I'm sure mine is now back to full power with the mods I've done. Larry |
05-25-2000, 12:33 AM | #10 |
Scooby Newbie
Member#: 75
Join Date: Jul 1999
Location: Farmington,CT,USA
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Stephen,
Its really the air density that matters. The density can be found by the Perfect Gas Law. The following link has a post by me that explains this a bit. http://www.i-club.com/ubb-files/Foru...ML/001551.html Basically, higher altitude means lower pressure, lower pressure means lower density. However, this can be offset some by the typically cooler temperatures at higher elevations. Cooler air higher density. Here's some basic altitude vs pressure info.. This does not account for pressure flucuations associated weather fronts and the like (i.e. high & low pressure areas) Altitude-----Pressure in ft-------lb/sq ft -5000--------2528 0------------2117 5000---------1761 10000--------1456 15000--------1195 20000--------973 25000--------786 30000--------630 35000--------499 40000--------393 [This message has been edited by Scooter (edited May 24, 2000).] |
05-25-2000, 12:35 AM | #11 |
Scooby Specialist
Member#: 52
Join Date: Jun 1999
Location: Naperville, IL
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Here is some intersting info http://www.gnttype.org/techarea/misc/altitude.html
It shows the conversion factors to convert 1/4 mile times an trap speeds to sea level and should give you an idea of the magnitude of change to expect. |
05-25-2000, 08:37 AM | #12 |
Scooby Specialist
Member#: 252
Join Date: Sep 1999
Location: San Antonio, TX
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From the results they got last night, at 6000 ft above sea level a stock car (2.2L at that) runs an 18 sec 1/4. Mark (w/slush box) running ~14psi only ran a 14.69. Damn this altitude!!!
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