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      11-01-2010, 02:32 PM   #1
shiv@vishnu
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Post Single turbos at Altitude

I was trying to participate politely in AR's single turbo thread but my posts kept getting deleted.

Here's the skinny on SAE/STD/etc, corrections on turbocharged engines at high altitude: The don't work. They are inaccurate and result in bloated "corrected numbers".

Directly from an engineer at Dynojet:
Quote:
The correction factors that we use in our dynamometer software are not
valid with forced induction applications. The most popular correction
factor, SAE CFJ1349 JUN90 and J1995 JUN95, does not account for the
conditions present in boosted applications. Atmospheric pressure is the
major component of this calculation, and anything that varies from the
standard (29.235 inHg) can easily be corrected for NA applications. When
you are forcing an "artificial atmosphere" into your motor, these
standards go out the window.

Technically any boosted car should be viewed as uncorrected if you want
to compare apples to apples. If we had a correction factor that just
took into account temperature and humidity, that may make things easier
to compare in boosted applications. If you are forcing 1 atmosphere
(14.7 psi) in your motor at 6,000 feet, or 1 atmosphere at 100 feet,
that's really the same difference.................IF you are measuring
manifold ABSOLUTE pressure, it's absolute, don't rely on a standard
boost gauge to give you an absolute value.

Regards,
----------------
Dan Hourigan
So how much does these "Corrections" bloat the HP numbers on a turbo car? The amount of bloat depends on the turbo system itself. If a turbo engine is capable of compensating for the thinner air by spooling harder and generating the same manifold pressure as it would at sea level, ALMOST NONE of this "correction" is needed.

Yes, running a turbo harder (ie, at a higher pressure ratio) does introduce higher intake temps and more exhaust backpressure. Both of which reduce power. However, almost all of the heat generated in the compression stage is removed by a good quality intercooler. So that loss is negligible. So you basically come down to exhaust backpressure increases. A large single turbo operating well within its flow limits will barely suffer from a slightly higher exhaust backpressure level. In fact, the only significant performance degradation will have to do with boost spool-up which will suffer noticeably. As far as power goes, however, the turbo will make roughly the same power as it would at sea level.

In the case of smaller factor twin turbos which are tuned close to their flow limits at sea level, the situation is different. In this case, the turbos aren't capable of compensating for the lower barometric pressure. Which means, at 5600', it doesn't see the same manifold pressure that it would see at sea level. Which means that it does lose considerable power at altitude. Which means that some (but not all) of that correction is suitable.

So applying altitude corrections on turbocharged engines is all flakey stuff. In some cases, the applied correction is just a little inaccurate. In some case, it's a lot inaccurate. Which is why YOU DON'T SHOULDN'T USE IT.

In the case of AR's 486whp dyno run, this number is fabricated by inappropriate dyno software, not by reality. The car actually put down 388whp assuming a 1.25 correction (we can only assume since AR wont disclose the actual correction). And it would put down close to that at sea level running the same absolute boost pressure.

Just my 2c,
Shiv
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      11-01-2010, 02:35 PM   #2
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If this is the case AR should find a dyno thats close to sea level as possible and see what the numbers will show...Thats one way of proving it that their numbers are legit....Plain and simple....Are there places in Colarado that has dynos close to sea level or they need to goto another state for this dyno?
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      11-01-2010, 02:39 PM   #3
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      11-01-2010, 02:43 PM   #4
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I suppose this is why we folk who have FI motors use STD vs SAE correction?
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      11-01-2010, 02:59 PM   #5
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Quote:
Originally Posted by themyst View Post
I suppose this is why we folk who have FI motors use STD vs SAE correction?
Neither STD and SAE corrections are applicable with turbo engines at altitude. They are largely interchangeable since they differ mainly in how they correct for humidity and temp. STD gives a slightly higher (usually 1-2%) number. At high altitude, all corrections should be ignored since they don't apply to turbocharged engines.
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      11-01-2010, 03:17 PM   #6
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No, what he's saying is that boosted cars should not use ANY correction. Uncorrected numbers are the only valid comparison for turbocharged cars. Sadly, there will be *some* altitude discrepancy on smaller turbos, but applying a broad correction (like 1.25... holy crap..) especially on an efficient turbo, would be misleading.
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      11-01-2010, 03:21 PM   #7
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I would have to disagree on some points here...

I live in Chicago and as many of you know Chicago is very close to sea level. We are often within 50 feet above sea level. I drive constantly around here and the vast majority of gas stations provide 93 octane.

So basically my level of measurement is 93 octane, very close to sea level.

My GF is from Denver. So far, since I've owned my 335, we've taken 3 trips to Denver. We've taken 2 more trips there prior to that including a 2-week long vacation around Colorado.

I can tell you from first hand experience that you can DEFINITELY feel a big difference in power due to the higher altitude. Both my 335 and my previous car felt neutered at the higher altitude. My 335 runs stock tune for now.

Also, on one of the trips we drove up to Pikes Peak which is over 14,000 feet in altitude. Let me tell you right away that the car felt significantly underpowered at such altitude.

The turbos may be able to push more air and compensate for the pressure difference, but it seems that you are forgetting that there is less oxygen at higher altitude!

Quote:
Atmospheric pressure and inspired oxygen pressure fall roughly linearly with altitude to be 50% of the sea level value at 5500m and only 30% of the sea level value at 8900m (the height of the summit of Everest). A fall in inspired oxygen pressure reduces the driving pressure for gas exchange in the lungs and in turn produces a cascade of effects right down to the level of the mitochondria, the final destination of the oxygen.

So even IF the turbos and the DME manage to compensate for the pressure drop, they cannot compensate for reduced oxygen content, simply because there are less molecules per unit volume of air!


Source: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1114067/


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Last edited by vasillalov; 11-01-2010 at 03:33 PM.
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      11-01-2010, 03:34 PM   #8
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Quote:
Originally Posted by vasillalov View Post
I would have to disagree on some points here...

I live in Chicago and as many of you know Chicago is very close to sea level. We are often within 50 feet above sea level. I drive constantly around here and the vast majority of gas stations provide 93 octane.

So basically my level of measurement is 93 octane, very close to sea level.

My GF is from Denver. So far, since I've owned my 335, we've taken 3 trips to Denver. We've taken 2 more trips there prior to that including a 2-week long vacation around Colorado.

I can tell you from first hand experience that you can DEFINITELY feel a big difference in power due to the higher altitude. Both my 335 and my previous car felt neutered at the higher altitude. My 335 runs stock tune for now.

Also, on one of the trips we drove up to Pikes Peak which is over 14,000 feet in altitude. Let me tell you right away that the car felt significantly underpowered at such altitude.

The turbos may be able to push more air and compensate for the pressure difference, but it seems that you are forgetting that there is less oxygen at higher altitude!




So even IF the turbos and the DME manage to compensate for the pressure drop, they cannot compensate for reduced oxygen content, simply because there are less molecules per unit volume of air!


Source: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1114067/


Aaaait?!
Did you read his post completely?

quote "
In the case of smaller factor twin turbos which are tuned close to their flow limits at sea level, the situation is different. In this case, the turbos aren't capable of compensating for the lower barometric pressure. Which means, at 5600', it doesn't see the same manifold pressure that it would see at sea level. Which means that it does lose considerable power at altitude. Which means that some (but not all) of that correction is suitable."
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      11-01-2010, 03:34 PM   #9
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Quote:
Originally Posted by vasillalov View Post
I would have to disagree on some points here...

I live in Chicago and as many of you know Chicago is very close to sea level. We are often within 50 feet above sea level. I drive constantly around here and the vast majority of gas stations provide 93 octane.

So basically my level of measurement is 93 octane, very close to sea level.

My GF is from Denver. So far, since I've owned my 335, we've taken 3 trips to Denver. We've taken 2 more trips there prior to that including a 2-week long vacation around Colorado.

I can tell you from first hand experience that you can DEFINITELY feel a big difference in power due to the atmospheric pressure. Both my 335 and my previous car felt neutered at the higher altitude. My 335 runs stock tune for now.

Also, on one of the trips we drove up to Pikes Peak which is over 14,000 feet in altitude. Let me tell you right away that the car felt significantly underpowered at such altitude.

The turbos may be able to push more air and compensate for the pressure difference, but it seems that you are forgetting that there is less oxygen at higher altitude!




So even IF the turbos and the DME manage to compensate for the pressure drop, they cannot compensate for reduced oxygen content, simply because there are less molecules per unit volume of air!


Source: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1114067/


Aaaait?!
Your power loss at 5600' was because the DME doesn't fully compensate for that kind of altitude. If you measure absolute manifold pressure, it will be lower than it would be at sea level. Hence the power loss. Not 25% loss. But some.

At 14,000' above sea level, more of the same. At 24,000', forget about it. At these very high altitudes (10,000' plus), reduced o2 content (%) also comes into play as you mentioned.

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      11-01-2010, 03:36 PM   #10
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So wait, you are saying that bigger turbos can magically enrich air with oxygen?! Really? Perhaps they should be giving big turbos to senior citizens instead of O2 canisters...
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      11-01-2010, 03:39 PM   #11
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Shiv, how does increasing the pressure at the manifold increase the O2 density in the air? No turbo can do that. All the DME and any tune can do is add more boost. Adding more boost won't magically oxygenate the air charge.
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      11-01-2010, 03:42 PM   #12
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Quote:
Originally Posted by vasillalov View Post
So wait, you are saying that bigger turbos can magically enrich air with oxygen?! Really? Perhaps they should be giving big turbos to senior citizens instead of O2 canisters...
::facepalm::

If I even attempt to post in thread I will most likely get banned.
You need to read a book about how turbos work.

Something to think about: If i push 20 psi out the stockers at sea level vs 20psi out of a gt35, which one do you think is going to have a harder time? Got it? Now why do you think its going to have a harder time? Got it?

Big turbos don't enrich air thats not there, however they use it more efficiently than a tiny one.
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      11-01-2010, 03:44 PM   #13
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Quote:
Originally Posted by vasillalov View Post
So wait, you are saying that bigger turbos can magically enrich air with oxygen?! Really? Perhaps they should be giving big turbos to senior citizens instead of O2 canisters...
From someone smarter than I:
Quote:
The partial pressure of oxygen at sea level is 14.7 PSI (pounds per square inch).

At 18,000 feet, the partial pressure of oxygen is half that. And at 36,000 feet, the partial pressure of oxygen is half that again. The decay rate is linear. This holds true until we get to outer space. In outer space, the point is moot.

Air is composed of oxygen (20-percent) and nitrogen (80-percent). Letís not quibble about 1-percent inert gasses. The composition remains the same regardless of altitude or temperature.

David E. Vogel, MSGT, USAF, Retired - Aerospace Physiologist
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      11-01-2010, 03:45 PM   #14
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im prepared for this thread.


yay common sense
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      11-01-2010, 03:48 PM   #15
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Hmm, I drove my 335i from 4,500 ft to sea level several times and could not tell much of a difference. My previous car, an e46 M3, there was huge power gain when I drove down to sea level, felt like someone put a supercharger on it.
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      11-01-2010, 03:48 PM   #16
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Ok I guess I stand corrected: as altitude increases, pressure changes but O2 content in air does not.
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      11-01-2010, 03:49 PM   #17
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The way I understood Shiv's post is that "at the same altitude", say 10000 feet, it is WRONG to use the same correction factor on differently sized turbos. Leaving PSI the same, between a larger and a smaller turbo, correction factors will be different. Correction factor on a smaller turbo that's not as efficient will be larger at higher altitude than for a larger turbo that's more efficient. This is why correction factors aren't portable across different turbo setups, especially at different barometric pressures...how does that sound?
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      11-01-2010, 03:54 PM   #18
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Close, however, once you've been around the block a coupl eof times you simply know not to use correction factors on trubo cars period. All they do is inflate numbers.
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      11-01-2010, 03:55 PM   #19
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Why has everyone, up until today, been reporting STD dyno results? Why not uncorrected???
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      11-01-2010, 04:04 PM   #20
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Quote:
Originally Posted by Clap135 View Post
Close, however, once you've been around the block a coupl eof times you simply know not to use correction factors on trubo cars period. All they do is inflate numbers.
Not true.
One of my dynos in the past showed higher numbers when uncorrected rather than corrected.
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      11-01-2010, 04:04 PM   #21
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Quote:
Originally Posted by dzenno View Post
The way I understood Shiv's post is that "at the same altitude", say 10000 feet, it is WRONG to use the same correction factor on differently sized turbos. Leaving PSI the same, between a larger and a smaller turbo, correction factors will be different. Correction factor on a smaller turbo that's not as efficient will be larger at higher altitude than for a larger turbo that's more efficient. This is why correction factors aren't portable across different turbo setups, especially at different barometric pressures...how does that sound?
Sounds about right. But it basically boils down to what is a correction factor and why should we/shouldn't we use it.

The purpose of a correction factor is just so that the ACTUAL dyno results (what the car actually puts to the ground) can be bumped up or down depending on how good/bad the testing conditions are. If they are very good, the numbers get nudged downwards. If they are very bad, they get nudged upwards. The idea is to provide an ESTIMATE on what the car would make in STANDARD conditions. When conditions aren't too far way from Standard conditions (mild humidity, room temp and at sea level), the corrections can be somewhat reasonable.

Does this estimate really mean anything to your or your car? Nope, not at all. It doesn't reflect what your car is actually making. It doesn't make your car any faster or any slower. All it does is SUGGEST that it could make more/less if conditions were different. In essence, all it does is give you numbers that you can compare to other results taken on other dynos in other days in other conditions.

For the most part, these estimates aren't perfectly accurate because the Dyno software doesn't know that some engines respond to different conditions differently. Things get really crazy when altitude is one of the atmospheric conditions that change. As the software correction for it is COMPLETELY inaccurate for turbo engines.

Last edited by shiv@vishnu; 11-01-2010 at 04:14 PM.
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      11-01-2010, 04:22 PM   #22
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Less oxygen up higher in the atmosphere is because there is less pressure. But once the air is compressed to say 14 psi, the density of oxygen is still the same... Its not like oxygen is more afraid of outer space than nitrogen and clings to the earth. So assuming the turbos can compress the air, the density is the same. yeah, you lose efficiency in the turbo do to working harder, however this is not nearly as big of an effect on a big turbo which they are touting so highly. I'm glad they are showing results, and I highly doubt that they intend to over exaggerate their results as in time we will all know the truth and its much better to UNDERRATE your product than the other way around.
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