Turbos at high altitude


#1

I was considering buying a 2005 Saab 9-3. In addition to being told Saabs have poor electrical systems, I also learned the 4 cyl turbos have difficulty at high altitude. I live at 7700 ft asl (2300m).



Can anyone tell more more about this? Would it only be Saab 4 cyl turbos that have a problem, or all? What about 6 cyl turbos?


#2

I have no idea why someone would tell you a turbocharged car has difficulty due to altitude.

Turbocharging helps an engine that is being operated at high altitudes.
This is why you see turbochargers and superchargers used on many aircraft; to cram that additional air into the intake.
The Aspen Colorado police dept. has used turbocharged SAABs for years and I think they are roughly 8500 feet above sea level.


#3

Yup. Turbos were originally developed for piston engine aircraft to prevent loss of power at higher altitudes.


#4

As already said, turbos are great at high altitudes.


#5

Excuse my ignorance. I was wondering if automotive turbochargers will open the waste gate at a set absolute manifold pressure or work on a pressure differential between the manifold pressure and atmospheric. Just curious.


#6

Turbo’s are superior to natural aspirated motors in the power aspect.


#7

Researcher, My understanding is that the waste gate opens at an certain differential in presure between the intake manifold and the outside air. If so, then the waste gate will open prematurely at high altitude since the outside air pressure is low.
The fix for this would be to increase the pressure before the waste gate opens by a couple of PSI.(depending on the altitude)


#8

all turbos run off of is your exhaust, and a few details left out, but youll be fine


#9

You might want to choose a more successful make and model. The electrical is just the most consistently unreliable part of a Saab. It has been rated poorly for some time now. The rest of the reliability fluctuates. The body is also foolish looking. People will always be asking you what year car it is. If you want to buy a car to show that you think you have money, get the Audi. Their reliability is consistently average. One Audi rates much like another Audi. Or get the right Volvo. Usually, people will buy one of these three makes because they heard that they were “good”.


#10

The Saabs problems are not limited to high altitude…

We hear a lot of Saab stories here…


#11

SAABs are not so bad. As an ex-SAAB tech I like them and my current SAAB Turbo (paid 20 bucks for it almost 2 years ago) has 210k on it now. I’ve got a ways to go to catch up with these guys.

http://www.saabnet.com/tsn/faq/miles/All.html


#12

Are you talking about the atmospheric pressure correction? Some ECU have such a function, some don’t. I’ve never driven a 2005 Saab 9-3 at the high altitude like that so can’t comment on that. I don’t think the cylinder count makes any difference.

As already mentioned before, altitude saps the power, no exceptions. However, increasing the boost pressure is not that easy since the compressor/turbine have its own characteristiscs(operational range), some works best at 1.1-1.4 bar, some at 2.5-3.0 bar so it has to be flexible(wide range) to do so otherwise the efficiency drops dramatically when it exceeds a certain point. Also, it would require modified fuel pumps, hose/connectors, hose clamps, exausts, charge air coolers for operating at higher pressure ratio than usual. Again, no ideas what kind of ECU the Saab have but it is possible that it might not have been designed to do well at high altitude.


#13

The 2003/2004 Saab 9-3 was a disaster. They corrected the issues in the recent ones. They tend to have more electrical problems than other cars.