[///AFRO]

Guys, I'm new here. Sorry if this is a repost. How come turbo's work harder and better in higher elevation. Is this true???

[Revlis]

Not true... While turbo's do eliminate much the power losses associated with elevation, (Roughly 3% per 1000') they do not start to work "Better" than they do at Sea level.

However they DO work better than any NA motor at elevation because of they do not rely on 14.7PSI to fill the cylinders.

As for Turbo's working harder? Not sure what you mean, accept that a clever engine management system would be holding the waste gate closed a little longer to achieve the same amount of cylinder pressure as it would at sea level. But the Turbo's are not going to be working harder themselves.

At least I'm pretty sure.

[///AFRO]

Originally Posted by Revlis

Not true... While turbo's do eliminate much the power losses associated with elevation, (Roughly 3% per 1000') they do not start to work "Better" than they do at Sea level.

However they DO work better than any NA motor at elevation because of they do not rely on 14.7PSI to fill the cylinders.

As for Turbo's working harder? Not sure what you mean, accept that a clever engine management system would be holding the waste gate closed a little longer to achieve the same amount of cylinder pressure as it would at sea level. But the Turbo's are not going to be working harder themselves.

At least I'm pretty sure.

Thanks alot Revils. I got what I needed.

[chbrules]

Forced induction works worse at higher elevations (unless they're some new special setup BMW has to variable adjust them). The reason being that the air molecules are more spaced out, less pressure, which means it's harder to get the same amount of pressure into the combustion chamber. You will most likely see a visible decrease in performance if you go 4000ft+ above sea level.

[xraymd]

Although as air density decreases, the turbo can spin faster as it encounters less resistance. Not enough to completely offset the change in elevation, but it does better than NA or supercharging. A supercharger is mechanically linked to the motor and therefore can't simply increase RPM's as air pressure decreases.

[Terry335]

Has anyone measured the boost at altitude to determine how the factory "overboost" system actually works?

[Insider]

Originally Posted by chbrules

Forced induction works worse at higher elevations (unless they're some new special setup BMW has to variable adjust them). The reason being that the air molecules are more spaced out, less pressure, which means it's harder to get the same amount of pressure into the combustion chamber. You will most likely see a visible decrease in performance if you go 4000ft+ above sea level.

Lots of wrong information above. The 335i can boost something like an additional 3psi of manifold boost to help compensate for elevation. At 4,500 ft you are losing about 2.2 psi of air pressure. So the 335i will have no problem compensating at that elevation. In other word, at 4,500 ft a normally aspirated car will lose 15% of its power, the 335i only a few percent.

[Terry335]

Originally Posted by Insider

Lots of wrong information above. The 335i can boost something like an additional 3psi of manifold boost to help compensate for elevation. At 4,500 ft you are losing about 2.2 psi of air pressure. So the 335i will have no problem compensating at that elevation. In other word, at 4,500 ft a normally aspirated car will lose 15% of its power, the 335i only a few percent.

I've heard people quote that .2bar number, but have you verified it with a boost gauge? Stock boost at sea level is around 8psi. Are people at 4,500 ft seeing 10.2psi?

[///AFRO]

thanx guys

[Insider]

Originally Posted by Terry335

I've heard people quote that .2bar number, but have you verified it with a boost gauge? Stock boost at sea level is around 8psi. Are people at 4,500 ft seeing 10.2psi?

I don't have my 335 yet, so I don't know. I think Shiv has some experience with it, however.

[jworms]

Originally Posted by Revlis

Not true... While turbo's do eliminate much the power losses associated with elevation, (Roughly 3% per 1000') they do not start to work "Better" than they do at Sea level.

However they DO work better than any NA motor at elevation because of they do not rely on 14.7PSI to fill the cylinders.

As for Turbo's working harder? Not sure what you mean, accept that a clever engine management system would be holding the waste gate closed a little longer to achieve the same amount of cylinder pressure as it would at sea level. But the Turbo's are not going to be working harder themselves.

At least I'm pretty sure.

right, except that the turbos do have to work harder to produce the extra boost necessary to compensate for the elevation. if the turbos max out at a certain PSI but the wastegate is staying closed beyond that point the turbos could blow from being overworked.

Originally Posted by Insider

Lots of wrong information above. The 335i can boost something like an additional 3psi of manifold boost to help compensate for elevation. At 4,500 ft you are losing about 2.2 psi of air pressure. So the 335i will have no problem compensating at that elevation. In other word, at 4,500 ft a normally aspirated car will lose 15% of its power, the 335i only a few percent.

the turbos will still make the same amount of boost at elevation it will just take longer to get there. because of this a turbo system will not lose any power as long as the turbos can handle the extra work. other than that, the only way i can see a turbo setup losing power at elevation is from the extra heat caused by the turbos having to work harder

[jworms]

Originally Posted by Terry335

I've heard people quote that .2bar number, but have you verified it with a boost gauge? Stock boost at sea level is around 8psi. Are people at 4,500 ft seeing 10.2psi?

it should be the same amount of boost. the wastegate is still going to open when it sees 8psi. that buffer of .2bar is probably what the stock turbos can handle before becoming inefficient/blowing.

[bilworth]

Udo Lindner was quoted in Eurotuner Magazine:
"We have two Mitsubishi turbos running at 0.6bar (8.8psi). These can boost to 0.8bar to compensate for altitude using the two electronically-controlled wastegates." Linder is the coupe's powertrain manager according to the article.

[mesier1111]

Originally Posted by Terry335

I've heard people quote that .2bar number, but have you verified it with a boost gauge? Stock boost at sea level is around 8psi. Are people at 4,500 ft seeing 10.2psi?

Originally Posted by bilworth

Udo Lindner was quoted in Eurotuner Magazine:
"We have two Mitsubishi turbos running at 0.6bar (8.8psi). These can boost to 0.8bar to compensate for altitude using the two electronically-controlled wastegates." Linder is the coupe's powertrain manager according to the article.

can we say.....

[Terry335]

Originally Posted by mesier1111

can we say.....

It would be nice if someone could verify on a boost gauge. I guess I'll have to do it myself.

[jworms]

Originally Posted by bilworth

Udo Lindner was quoted in Eurotuner Magazine:
"We have two Mitsubishi turbos running at 0.6bar (8.8psi). These can boost to 0.8bar to compensate for altitude using the two electronically-controlled wastegates." Linder is the coupe's powertrain manager according to the article.

i take that to mean that the turbos have the ability to run at +0.8 bar to achieve the same stock boost at higher elevation that they would get with sea level. if the elevation was high enough that 0.8bar wasn't enough to compensate for the air density loss then you would get less than stock boost or even much worse, blown turbos.

[bilworth]

Originally Posted by jworms

i take that to mean that the turbos have the ability to run at +0.8 bar to achieve the same stock boost at higher elevation that they would get with sea level. if the elevation was high enough that 0.8bar wasn't enough to compensate for the air density loss then you would get less than stock boost or even much worse, blown turbos.

The way I read the article, the engine will increase boost up to the 0.8 Bar and then the boost/HP will begin to fall off. I think it will hold sea level HP up to about 6000' msl if my calculations are correct. That's assuming standard temperature etc. It would be interesting to see what a gauge would read though.

[jworms]

Originally Posted by bilworth

The way I read the article, the engine will increase boost up to the 0.8 Bar and then the boost/HP will begin to fall off. I think it will hold sea level HP up to about 6000' msl if my calculations are correct. That's assuming standard temperature etc. It would be interesting to see what a gauge would read though.

it's pretty simple, if the boost level is more than what it makes at sea level you will make more power than what you would at sea level. the engine doesn't know/care that you are running at higher elevation, all it knows is that it needs to make boost until the wastegate opens (which is whatever the stock boost level is). the elevation just means that the turbos have to push more less dense air to make the same amount of boost, but they will eventually make that same amount of boost (as long as they can do so).

1 bar at sea level is not = to 1.8 bar at high elevation
it's like asking what's heavier, a pound of feathers or a pound of gold?

if the car actually produces more boost at high elevation then somebody should make a drag strip at the top of a mountain because your car will have more power than it would at sea level

[Insider]

Originally Posted by jworms

it's pretty simple, if the boost level is more than what it makes at sea level you will make more power than what you would at sea level. the engine doesn't know/care that you are running at higher elevation, all it knows is that it needs to make boost until the wastegate opens (which is whatever the stock boost level is). the elevation just means that the turbos have to push more less dense air to make the same amount of boost, but they will eventually make that same amount of boost (as long as they can do so).

1 bar at sea level is not = to 1.8 bar at high elevation
it's like asking what's heavier, a pound of feathers or a pound of gold?

if the car actually produces more boost at high elevation then somebody should make a drag strip at the top of a mountain because your car will have more power than it would at sea level

What matters is what the total absolute pressure is. Atmosphere pressure plus what ever boost the turbos make. For example, at sea level the pressure is 14.7 psi. At 4,500 ft it is about 12.5 psi. At sea level the car makes 8.5psi (manifold pressure) plus 14.7 psi atmosphere pressure for a total absolute pressure of 23.2 psi. At 4,500 ft the manifold pressure should increase to 10.7 psi. Plus 12.5 atmosphere pressure would equal the same absolute pressure of 23.2. The computer is going to try to get to the absolute pressure. So the car would make more boost (10.7 manifold pressure versus 8.5) but make the same power since there is less atmospheric pressure to begin with at high elevations

[jworms]

Originally Posted by Insider

What matters is what the total absolute pressure is. Atmosphere pressure plus what ever boost the turbos make. For example, at sea level the pressure is 14.7 psi. At 4,500 ft it is about 12.5 psi. At sea level the car makes 8.5psi (manifold pressure) plus 14.7 psi atmosphere pressure for a total absolute pressure of 23.2 psi. At 4,500 ft the manifold pressure should increase to 10.7 psi. Plus 12.5 atmosphere pressure would equal the same absolute pressure of 23.2. The computer is going to try to get to the absolute pressure. So the car would make more boost (10.7 manifold pressure versus 8.5) but make the same power since there is less atmospheric pressure to begin with at high elevations

absolute pressure is not an accurate way of measuring boost as you have proven by mentioning the different atmospheric pressures at different elevations. the car is going to make that 1 atmosphere of pressure no matter what, even without the turbos. this is why N/A and S/C cars are hurt so much by high elevation...their manifold pressure is actually lessening because of it. boost is everything after that 1 atmosphere. the wastegate will stay closed until the preset boost is achieved (8.5psi) no matter what. once the turbos achieve 8.5psi the wastegate will open. that's the beauty of a turbo setup, they create their own atmosphere. why would manifold pressure increase with a turbo setup at higher elevation if the wastegate is opening at the same time (psi) it would at sea level?

y'know, we might be agreeing on the same thing because i'm still a little confused by what you wrote

here's something i found after a very brief search. not very technical but it seems to regurgitate what i've been saying (2nd letter on there): http://www.roadandtrack.com/article....rticle_id=5030

[bilworth]

I thought the computer looks at the absolute manifold pressure for reference.
In this case: 1.0 BAR (14.7 psi) + 0.6 BAR (8.8 psi) = 23.5 psi. So, the computer will try to maintain 23.5 psi. As the elevation increases, the 14.7 part of the equation decreases so the 8.8 part has to increase to maintain the 23.5 psi. The computer does this by regulating the wastegate up to a maximum of 0.8 BAR (11.8 psi). So, that means it should be able to maintain the 23.5 psi up to an elevation where the atmospheric pressure equals 11.7 psi (11.7 + 11.8 = 23.5). That elevation is approximately 6000' msl on a day when standard temperature and pressure prevail. Am I wrong?

[Insider]

Originally Posted by jworms

absolute pressure is not an accurate way of measuring boost as you have proven by mentioning the different atmospheric pressures at different elevations. the car is going to make that 1 atmosphere of pressure no matter what, even without the turbos. this is why N/A and S/C cars are hurt so much by high elevation...their manifold pressure is actually lessening because of it. boost is everything after that 1 atmosphere. the wastegate will stay closed until the preset boost is achieved (8.5psi) no matter what. once the turbos achieve 8.5psi the wastegate will open. that's the beauty of a turbo setup, they create their own atmosphere. why would manifold pressure increase with a turbo setup at higher elevation if the wastegate is opening at the same time (psi) it would at sea level?

y'know, we might be agreeing on the same thing because i'm still a little confused by what you wrote

here's something i found after a very brief search. not very technical but it seems to regurgitate what i've been saying (2nd letter on there): http://www.roadandtrack.com/article....rticle_id=5030

My understanding is that there is an extra 3psi of boost available in the manifold to compensate at higher elevations. So the ECU will measure absolute boost pressure, and it will try to reach the absolute number. Therefore, the manifold pressure will be higher at elevation because that's what it takes to reach the same absolute pressure that the car has at sea level.