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To turbo or not for Colorado elevation?


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17 replies to this topic

#1 Beowulf

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Posted 15 June 2005 - 10:13 PM

I am brand new to Subarus. My parents are looking to get an Outback wagon. Should they get the 3.0 or the 2.5 turbo for driving around the mountains of Colorado?

#2 SilverSubie

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Posted 15 June 2005 - 10:23 PM

Just IMHO... No replacement for displacement. Less wear and tear on the motor and less potential problems, though, turbos have come a long way in terms of effeciency and reliability.


Follow up question. Does anyone know if putting a turbo timer in voids any of the factory warranty?

#3 Blue84Hatch

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Posted 15 June 2005 - 10:29 PM

Yo go with the turbo. I live in New Mexico and go snowboarding a lot in the winter in CO and cruise all over Colorado. Over mountain passes and on the highways. I have a Forester XT, which has the a 2.5 turbo and it screams. I think the Forester was actually designed for the mountains. It runs great in all elevations. Of course it does have a STI setup now, but before I put that on it it was still a hell of a Subaru. I would go with the turbo for sure. Especially in CO.

Peace

#4 Brumby Boy

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Posted 16 June 2005 - 04:06 AM

No coment on what car to buy as i live in the sunny tropics of Queensland Australia, but...

Follow up question. Does anyone know if putting a turbo timer in voids any of the factory warranty?


I dont belive so but just check with your dealer.

#5 Sweet82

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Posted 16 June 2005 - 10:36 AM

I'm not really sure it would matter based on elevation, the car should be set up to run at it's point of sale and the computer should compensate for everything else.

I'd say it's probably just a simple matter of personal preference... :rolleyes:

Oh ya, WELCOME TO THE BOARD!

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82 SubaruHummer--will be spending it's golden years at 8000 to 9500 ft.
01 Forester--runs between 4500 - 8000 ft regularly.

#6 DerFahrer

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Posted 16 June 2005 - 11:20 AM

You have the right idea, you're asking the question based on the elevation where you live.

Turbo cars do very well in high elevations because the lower pressure that results is irrelevant. The engine is force-fed by the turbo and doesn't have to rely on only its vacuum to gather air from the outside.

Take an N/A car up to a high elevation and take the same car in a turbo variant with it. You will notice how the N/A car begins to run out of breath and the turbo car seems unaffected.

Do realize that turbo cars require more maintenance as suggested, and that a turbo engine will almost always have a dead spot where the turbo isn't spooling fast enough to provide any power boost.

But I do actually think if a car is to stay in a high-elevation area, that the engine will benefit and even last longer if it has the benefit of forced induction.

#7 Beowulf

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Posted 16 June 2005 - 01:35 PM

I definetly agree that turbos on the 2.5 is the way to go if you live at elevation. BUT, with the 3.0 being a little bigger displacement I was wondering how it might do at say 10,000 feet. Normally N/A's will loose around 15% or more because of the elevation. Turbos don't loose nearly that much. I need to go test drive both a 2.5 turbo and the 3.0 for them at 6K plus elevation. If I get a chance to do that I'll report back and let you know how it goes.

#8 hklaine

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Posted 16 June 2005 - 03:25 PM

Turbo cars do very well in high elevations because the lower pressure that results is irrelevant. The engine is force-fed by the turbo and doesn't have to rely on only its vacuum to gather air from the outside.


The turbo helps increase the pressure, but this increase is relative. It is relative to the pressure around the turbo. The post-turbo pressure is not an absolute pressure independent of its surroundings.

There was a bit of a similar discussion some time ago here.
Physics can be a real bi$%h when it comes to performance.

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#9 DerFahrer

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Posted 17 June 2005 - 12:11 AM

The turbo helps increase the pressure, but this increase is relative. It is relative to the pressure around the turbo. The post-turbo pressure is not an absolute pressure independent of its surroundings.


You are correct. But we're only talking a mile up. I would think the post-turbo pressure would be negligibly affected.

#10 Hondasucks

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Posted 17 June 2005 - 12:58 AM

yeah get the turbo, my fiancee's Impreza runs out of breath going over the summit but my turbowagon does just fine :D

#11 Scoobaroo

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Posted 17 June 2005 - 09:38 AM

I definetly agree that turbos on the 2.5 is the way to go if you live at elevation. BUT, with the 3.0 being a little bigger displacement I was wondering how it might do at say 10,000 feet. Normally N/A's will loose around



Regardless of displacement, an NA engine will produce around 3% less HP for every 1000 ft. rise in elevation from seal level. Fuel injected engines can compensate somewhat by leaning the fuel mixture and advancing ignition timing, but the HP loss is due to a loss in real barometric pressure ( the amount of natural air pressure waiting on the opposite side of the throttle plate.) and air density.

There is a curve to the HP loss. under 4,000 ft. or so, the loss may not even be noticable (seat of the pants) once the computer has compensated for the lower air density. At 10,000+ ft, the loss in air density becomes exponentially greater. At thest elevations, you've most likely lost around 35-40% of HP.

Air temperature and humidity are factors also.

#12 hklaine

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Posted 17 June 2005 - 12:27 PM

You are correct. But we're only talking a mile up. I would think the post-turbo pressure would be negligibly affected.


I would guess at a mile up you would lose +/- 3 psi. There are plenty of calculations you can do for this, but I am just guessing from what I remember to be correct. :-\

-Heikki

Edit:Pressure at 1 mi. is ~83% of the pressure at sea level for those interested in the numbers...

1.00 ATM = 14.69595 psi
0.83 ATM = 12.19764 psi


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#13 Beowulf

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Posted 17 June 2005 - 01:54 PM

At loosing 30-40% at full elevation here I think it would behouve them to get the 2.5 turbo. The 3.0 would only drop to 175 to 150 hp at 10,000 feet, BUT that might be too much of a drop. I don't want them later wishing they had bought the turbo. Thank you everyone for your help and input.

If you ever need advice on Jeeps or Volvo's hopefully I can give some help back.

#14 Beowulf

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Posted 17 June 2005 - 01:56 PM

One last question.


Hondasucks,

What engine does your fiancee's Impreza have?

#15 DerFahrer

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Posted 18 June 2005 - 02:46 AM

I would guess at a mile up you would lose +/- 3 psi. There are plenty of calculations you can do for this, but I am just guessing from what I remember to be correct. :-\


That much huh? I didn't think it would be that drastic...

#16 BeefaRu

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Posted 18 June 2005 - 10:10 AM

Regardless of displacement, an NA engine will produce around 3% less HP for every 1000 ft. rise in elevation from seal level. Fuel injected engines can compensate somewhat by leaning the fuel mixture and advancing ignition timing, but the HP loss is due to a loss in real barometric pressure ( the amount of natural air pressure waiting on the opposite side of the throttle plate.) and air density.

There is a curve to the HP loss. under 4,000 ft. or so, the loss may not even be noticable (seat of the pants) once the computer has compensated for the lower air density. At 10,000+ ft, the loss in air density becomes exponentially greater. At thest elevations, you've most likely lost around 35-40% of HP.

Air temperature and humidity are factors also.

So THATS why my EJ22 loses so much oomph the last mile before Eisenhower tunnel in Co. --E

#17 Scottbaru

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Posted 18 June 2005 - 10:35 AM

B!

We need a flipoff button on this forum...

#18 Scottbaru

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Posted 18 June 2005 - 11:08 AM

First, you should be talking them into an FZJ80! What kind of son are you?? Otherwise, I like the turbo, not sure about the 2.5liter. Do a search on headgaskets, here or any Subaru forum. Search used Subarus online, and note how many need engines or have new engines. My neighbors have an '04 L.L.Bean Limited Outback wagon with the 3.0l, sweet car. They've had trouble with the brake rotors, bad alloy according to the service bulletin he found online.




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