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Old 12-30-2001, 11:16 AM   #1
Drjosh
Scooby Newbie
 
Member#: 8226
Join Date: Jul 2001
Location: Denver
Vehicle:
2002 WRX sedan
Midnight black pearl

Default Temp/altitude and boost

My newbie-level understanding (all other things equal) is:

Higher altitude = lower boost
Colder temp = higher boost

How do these variables interact?

Us Rocky Mountain guys have to deal with both daily, and the extremes of both everytime we drive to the moutains (Denver is 5280 ft, to go skiing you have to go through Eisenhower tunnel ~ 11,000 ft).

I'm just worried about overboosting in cold temps, as has been reported recently.

P.S. I have a longer post in the Rocky Mountain Forum on this same topic directed at local folks.
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Old 12-30-2001, 04:46 PM   #2
nmyeti
Scooby Specialist
 
Member#: 4980
Join Date: Mar 2001
Location: Albuquerque, NM USA
Default Re: Temp/altitude and boost

Quote:
Originally posted by Drjosh
My newbie-level understanding (all other things equal) is:

Higher altitude = lower boost
Colder temp = higher boost

How do these variables interact?

Us Rocky Mountain guys have to deal with both daily, and the extremes of both everytime we drive to the moutains (Denver is 5280 ft, to go skiing you have to go through Eisenhower tunnel ~ 11,000 ft).

I'm just worried about overboosting in cold temps, as has been reported recently.

P.S. I have a longer post in the Rocky Mountain Forum on this same topic directed at local folks.
I have recently had the blessing/curse of taking my WRX from my home in Albuquerque, NM (5200 feet) to visit my in-laws in Kansas City, MO (like 800 feet?) and made the following observations...

When i left my turboxs MBC was set for about 1.25-1.3 bar for our altitude. When i got to Kansas city, the very first time i jumped on the gas, i pegged my 1.5 bar boost gauge!

Turned it down to 1.3 bar or so, and when i got back up to albuquerque, it was closer to 1.1-1.2 bar of boost.

The car drives MUCH better at sea level than it ever did up here in albuquerque. In fact i have pretty much been depressed with the way it drives ever since i got back up here because its just so much slower both on boost and off.

In KC i would get 1 bar of boost by about 3500rpms, in ABQ its closer to 4500rpms before i get that kind of boost. In KC, the car would drive quite happy at 55-60mph in 5th gear and accelerate well i if i rolled on the gas. In albuquerque, 55-60mph is 4th gear duty because there is no low end torque in that rev range up here.

All the way around the car was better down there... its sad really, but i am sure going to a sea level track when its time to run again. Enough of this lousy 5200 feet crap.

-Nathan
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Old 12-30-2001, 05:28 PM   #3
StefWRX
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Member#: 12828
Join Date: Nov 2001
Vehicle:
2002 WRX
WRC Blue Pearl

Default

Well first off, the higher the altitude, the less dense the air is outside. Less air outside means less air in the engine= less power. As far as heat is concerned, same thing applies, as heat rises, air density decreases. Try running your car in July like you run in Nov/Dec. You will notice the car is much more sluggish in the summer. The same theories apply to tubros/intercoolers/etc. The more efficient the turbo, the more air it can force into the engine without creating HEAT. Also, the more air you can cool through your intercooler will result in more power because cool air is more dense, and the more air you can cram in the cylinders (with the right amount of fuel), the more power the engine will make. Timing and fuel mixtures come in to play too, but you get the general idea.

Stefan
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Old 12-30-2001, 10:50 PM   #4
tdman77
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Member#: 9832
Join Date: Aug 2001
Chapter/Region: South East
Location: Orlando, FL
Vehicle:
2022 WRX
Magnetite Gray

Default

When I dynoed my car last month at TurboXs the boost was set to 15.6psi. Now that the weather has gotten colder I see my boost creeping to 16-16.5psi. The other day (20deg F) I saw a spike of 19psi but did not get an overboost CEL. Reset the computer anyways and now the car seems to have settled down with boost running around 16psi.

Oh yeah I have a unichip.
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Old 12-31-2001, 12:11 PM   #5
Drjosh
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Member#: 8226
Join Date: Jul 2001
Location: Denver
Vehicle:
2002 WRX sedan
Midnight black pearl

Default Bueller, Bueller....

Bump. Anyone else have thoughts about this?
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