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Old 04-29-2009, 01:30 PM   #1
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Turbo-charged power loss at elevation?

My buddy Bob and I were talking about the effects of turbocharged cars and the loss of hp at elevation. He is big DSM guy and has had the same argument on the DSM forums.

He knows the math and pressure differences much better than me. What I know is its hard to make power at 6000'.

Here is his explanation and you can a lot is going on that most people do not realize or think about.

Stock viggen dyno plot in Sae and the same plot in uncorrected, page 3.

John
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Old 04-29-2009, 02:29 PM   #2
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T7 cars correct for altitude...up to 15k feet. My Viggen put down the same power in Boulder (uncorrected) as it does in Boston (also uncorrected). I would never want to have a "max effort" T7 car at sea level and then drive it up into the mountains - I don't want it lean out and ping itself to death....

Based off of your arguement that you still need to "correct" for a T7 car - I should have never gotten rid of my 2nd Viggen - in stock form it was putting down 280 something HP at the wheels when the numbers were "corrected" - just imagine if I had put a tune on it. Hell - even my V70R puts down 433 HP at sea level and 433 HP in Denver (uncorrected)...or should I say 550ish corrected HP and run around on the Volvo R forums claiming to have over 550 HP just off of bolt ons and a tune? - I'd get rediculed.

My Hirsch tune puts more power down then your tunes you rave about with less boost - and I know that I'm not running "max out" (I did a lot of logging on the passes to make sure I wouldn't blow a motor). The guys that I know that are running Maptun, SQR, and Nordic in Colorado aren't running "max out" with their turbos at mile high......and when they have dyno'd them at mile high and in Chicago or else where at lower elevations their uncorrected numbers are +/- 1% And many of them have logged data going over the passes to make sure they are ok.

The question is - how will your tunes stand up over time with them being so "maxxed out"? Are your tunes safe for every day driving?

Even the EVO/STi tuner on Arapahoe Drive in Boulder won't give you a "corrected" dyno with a turbo car unless you ask for your numbers to be "corrected" - the STi/EVO crowd don't compare their tuning numbers at altitude with "corrected" numbers.....

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Old 04-29-2009, 02:35 PM   #3
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My buddy Bob and I were talking about the effects of turbocharged cars and the loss of hp at elevation. He is big DSM guy and has had the same argument on the DSM forums.

He knows the math and pressure differences much better than me. What I know is its hard to make power at 6000'.

Here is his explanation and you can a lot is going on that most people do not realize or think about.
Buddy Bobs comment are pretty much valid as written and think majority who have looked into how a turbo works are familiar what these issues.
However the mail pretty much concentrates on what happends when you in term of flow get near to the right edge on the map and as I tried to write to you in the other topic that there arent too many who would run a car "maxed" in rpm area where the turbo spools and in rpm area which follows there after and end before the flow ruled by HW begins to fall.
This naturally causes a problem how to apply the CF when the need for it is greatly dependant on the "margin", just like buddy bob wrote "The difference is when a car ISN'T max effort....you can turn up the boost and flow the same at elevation ...."

Other topic is also how many can outflow their compressor in real life? Sure its easy to be done with unit like 15T, but once in the region of 28, 71 etc other issues come into play and engine "refuses" to swallow to air thus you yank up the boost.

So in shortness the CF is and will always be a guess if not tested and applied case by case manner. I think we all can agree that it harder to make power if air is thinner just as the case is if the ambient temp is much hotter, nothing abnormal in that.
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Old 04-29-2009, 02:42 PM   #4
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T7 cars correct for altitude...up to 15k feet. My Viggen put down the same power in Boulder (uncorrected) as it does in Boston (also uncorrected). I would never want to have a "max effort" T7 car at sea level and then drive it up into the mountains - I don't want it lean out and ping itself to death....

Based off of your arguement that you still need to "correct" for a T7 car - I should have never gotten rid of my 2nd Viggen - in stock form it was putting down 280 something HP at the wheels when the numbers were "corrected" - just imagine if I had put a tune on it. Hell - even my V70R puts down 433 HP at sea level and 433 HP in Denver (uncorrected)...or should I say 550ish corrected HP and run around on the Volvo R forums claiming to have over 550 HP just off of bolt ons and a tune? - I'd get rediculed.

My Hirsch tune puts more power down then your tunes you rave about with less boost - and I know that I'm not running "max out" (I did a lot of logging on the passes to make sure I wouldn't blow a motor). The guys that I know that are running Maptun, SQR, and Nordic in Colorado aren't running "max out" with their turbos at mile high......and when they have dyno'd them at mile high and in Chicago or else where at lower elevations their uncorrected numbers are +/- 1% And many of them have logged data going over the passes to make sure they are ok.

The question is - how will your tunes stand up over time with them being so "maxxed out"? Are your tunes safe for every day driving?

Even the EVO/STi tuner on Arapahoe Drive in Boulder won't give you a "corrected" dyno with a turbo car unless you ask for your numbers to be "corrected" - the STi/EVO crowd don't compare their tuning numbers at altitude with "corrected" numbers.....
Read the information again, it will correct if you have some power/efficiency left in the car, a stg 3-4 is maxed out

It has nothing to do with my tunes or anyone elses, it has everything to do with is there any reserve left

If you made the same power in uncorrected, it means you did not have your system close to being maxed out. There is only 20% in reserve from a stock set-up. Post your dyno slips and this will be evident. I have pleanty of dynos that prove the opposite of what you are saying. Two of them are the tuners you stated

Read the information again!

John
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Old 04-29-2009, 02:44 PM   #5
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Buddy Bobs comment are pretty much valid as written and think majority who have looked into how a turbo works are familiar what these issues.
However the mail pretty much concentrates on what happends when you in term of flow get near to the right edge on the map and as I tried to write to you in the other topic that there arent too many who would run a car "maxed" in rpm area where the turbo spools and in rpm area which follows there after and end before the flow ruled by HW begins to fall.
This naturally causes a problem how to apply the CF when the need for it is greatly dependant on the "margin", just like buddy bob wrote "The difference is when a car ISN'T max effort....you can turn up the boost and flow the same at elevation ...."

Other topic is also how many can outflow their compressor in real life? Sure its easy to be done with unit like 15T, but once in the region of 28, 71 etc other issues come into play and engine "refuses" to swallow to air thus you yank up the boost.

So in shortness the CF is and will always be a guess if not tested and applied case by case manner. I think we all can agree that it harder to make power if air is thinner just as the case is if the ambient temp is much hotter, nothing abnormal in that.
Right, its what I have said many times, a stock t7 viggen will make more boost and make more power. If that same car is a stg 3 or 4, there is very little left to give and it will lose power. The norm for a 300bhp car seems to be right around 40whp. Its not an exact number, but close,

John
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Old 04-29-2009, 02:57 PM   #6
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John please read my post again and dont read from between the lines "things" what are not written in that post.
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Old 04-29-2009, 03:11 PM   #7
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I am just going to say, yes, its not an exact number and yes, there can be some differences and it all depends on how much reserve you have. I know some tuners are pretty close and some leave a little more on the table. That will directly effect what is lost. I will go along with you on that.

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Old 04-29-2009, 05:02 PM   #8
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Here are a couple things I thought of as I read through this.

#1 All horsepower numbers that are "uncorrected" are useless numbers and can not be compared to other "uncorrected" numbers.

There are many parameters that need to be taken into account when an operator wants to ensure good repeatable numbers no matter if the car is at 0 ft or 6000 ft. The difference in Barometric Pressure, Relative Humidity, and Temperature alone can greatly vary the CALCULATED horsepower number. That is why CF formulas were developed so you could get "corrected" numbers that could be compared between other numbers no matter what the location or environment the test was conducted in. Much less on top of that if you want to compare those numbers the same CF formula must be used. IIRC all Superflow dynos (unless programmed other wise) utilize their own in house designed CF formula while Mustangs use a SAE formula (J1995 IIRC). The reason why many people like the uncorrected numbers is because a guy at sea level with very few modifications could have the same horsepower as a guy that had poured a lot of work into their engine at high altitude.

#2 A stock T7 car will make more boost but not to make more power. Just enough to make what it's supposed to per the conditions the car is in.

A stock T7 engine will flow as much air as it can to try to make the power it is programmed to make. That is why people who put boost gauges on their stock T7 cars get all fired up that when they were in the mountains their car was running 13 psi of boost but at sea level may only be running 7 psi. So lets say its a 9-5 Arc programmed to make 220 Hp it will run as much boost is needed to allow the engine to make it's 220 Hp at sea level or at altitude. It won't make more power.
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Old 04-30-2009, 08:01 AM   #9
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I see you have a good understanding of how it works and why I only use the sae to compare changes on the same dyno with the same car.

The write-up re-states what I have been saying for years and what you said, a t7 car will increase boost/airmass to try and maintain the same power at eleveation. They have say 20% in reserve. When you have a stg 3-4 tune made, it eats up that reserve in varying degrees, many are eating up most of it and some leave a little on the table, say 5%.

You bring that same car up to elevation at 6000', where I am, it will either have little to no reserve left and lose a good little chunch of power or may lose a little less if there is 5% left on the table with the sea-level tune.

Its really very simple, we know the stock 15t is efficient to right around say 18-20psi, if you have a stg 4 at sea-level with 20psi, there is no room to come up to elevation and make more boost, its that simple, the margin of dimininshing returns is present. It does not help much to push the stock 15t to 25psi.

So, the theory applies to t7 cars, t8 cars or whatever, the closer to being maxed out you are, the more hp you will lose at elevation.

John
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Old 04-30-2009, 12:59 PM   #10
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Its really very simple, we know the stock 15t is efficient to right around say 18-20psi, if you have a stg 4 at sea-level with 20psi, there is no room to come up to elevation and make more boost, its that simple, the margin of dimininshing returns is present. It does not help much to push the stock 15t to 25psi.

So, the theory applies to t7 cars, t8 cars or whatever, the closer to being maxed out you are, the more hp you will lose at elevation.

John
I recall you quoted you have 200 dynosheets from your tunes or something like that, so could you post stage III uncorr dyno reusults from denver or other hihger altidue places? I asked from them in the other tread but you skipped that question.

Anyhow do I remeber wrong but wasnt the saab 9-5 aero lauched at a ski resort in Us. at roughly 9000ft and the measurement from there met the sea level figures. That would mean based on billy bobs comments that there would be indeed 30% in reserve and as we know 230*1.3 = 300bhp which can be achieved at sea level with the 15T.

And again we all know that its harder to make bhp when it hot or air is thin compared thicker and colder, but trying to make rule of thumb rules to "explain" it all goes no where and like said what is in reserve is greatly dependant on the revs at stake.
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Old 04-30-2009, 07:21 PM   #11
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I agree that at a higher altitude the air is much thinner than at sea level meaning that less air gets slammed into the turbo, but that thinner air also causes a greater pressure differential between the gasses in the exhaust and the ambient air, which means the exhaust will flow out faster. Thats one of the biggest reasons airplanes started using turbos way back when they were first created; the higher they went, the greater the pressure differential so the turbo could make up for the loss due to thin air since the turbo would be running more efficient.

That said I don't know just how much of a benefit that pressure differential serves but I do doubt that it entirely makes up for the absence of thicker air being slammed into the engine.

my 2c
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Old 04-30-2009, 08:42 PM   #12
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The write-up re-states what I have been saying for years and what you said, a t7 car will increase boost/airmass to try and maintain the same power at eleveation.
That's a typo right?
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Old 05-01-2009, 07:29 AM   #13
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I agree that at a higher altitude the air is much thinner than at sea level meaning that less air gets slammed into the turbo, but that thinner air also causes a greater pressure differential between the gasses in the exhaust and the ambient air, which means the exhaust will flow out faster. Thats one of the biggest reasons airplanes started using turbos way back when they were first created; the higher they went, the greater the pressure differential so the turbo could make up for the loss due to thin air since the turbo would be running more efficient.

That said I don't know just how much of a benefit that pressure differential serves but I do doubt that it entirely makes up for the absence of thicker air being slammed into the engine.

my 2c
Well, sure, its like Eric said, you might want to listen to people that live at high elevation before people that just use numbers to calculate loss. When you read Bob's write-up about all the effects of heat and density loss with the turbo and the ic, etc, it becomes a lot easier to understand what we are up against when trying to make power at elevation.

I have done a lot of racing up here and it always is the same story with the guys that live here and talk about it. When you first move up here you are blown away at the effects

It should be interesting at this year's SOC,

John
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Old 05-01-2009, 07:37 AM   #14
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I recall you quoted you have 200 dynosheets from your tunes or something like that, so could you post stage III uncorr dyno reusults from denver or other hihger altidue places? I asked from them in the other tread but you skipped that question.

Anyhow do I remeber wrong but wasnt the saab 9-5 aero lauched at a ski resort in Us. at roughly 9000ft and the measurement from there met the sea level figures. That would mean based on billy bobs comments that there would be indeed 30% in reserve and as we know 230*1.3 = 300bhp which can be achieved at sea level with the 15T.

And again we all know that its harder to make bhp when it hot or air is thin compared thicker and colder, but trying to make rule of thumb rules to "explain" it all goes no where and like said what is in reserve is greatly dependant on the revs at stake.

I think its amusing that you are hanging onto that last little bit of "window" of difference. Its not really that hard to get close, I do have some dynos, but I said I have near 200 tunes out there now, only maybe 10-15 dyno sheets.

Just think of the turbo 15T, most tuners put the efficiency of the turbo right around 20psi, right? So, if you have a stg 3+ and you are making good power at 20psi at sea-level, where is that turbo going to go to make the extra power? You know better than me exactly how it works, but we both know that same turbo that is near its efficeny limit cannot go to 25-27psi and make up for the power

I have seen stock viggens make 15psi here in Denver to maintain the same 230bhp that the car made at sea-level at 8psi. That is a 7psi increase to maintain the power. You cannot go from 20psi to 27psi and still be efficient, you lose power.

Say you have a mild stg 3 that runs 15-16psi, then you have a little room, I will give you that.

The bottom line is the closer you are to efficiency limit, the close you are to maxing out your turbo and the more hp you will lose. This is all without even considering the loss in octane in fuel or the ic effects or the heat dissipation of the headers and turbine.

John
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Old 05-01-2009, 07:43 AM   #15
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I always understood Viggen literature to mean, the cars were capable of producing UPTO 20.3lbs of boost. Meaning, my car does not produce 20.3lbs of boost, it is at sea level. It is all about target airmass, and that might equate to a healthy Viggen dyno of say 210whp on an average sea-level Dynojet. BUT at higher evelvations, T7 will adapt by increasing boost UPTO 20.3psi to achieve that SAME target airmass and should make that same 210whp.

Now, what was said does make sense. That this happens because the stock turbo is not maxed out and has the room to compensate. But if its a modified car, say stage 4 and running a completely stock turbo, it might not be able to compensate in the same way because it does not have the room without operating out of its efficiency range. I cannot say for sure, but one would think that in that situation there COULD be a difference in sea level and high elevation dyno numbers. The size of that difference is even more debatable.
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Old 05-01-2009, 08:12 AM   #16
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I think that is the best explanation I have heard yet about your persistence to this point.

It does make sense so long as tunes at sea-level really are up in the 95% efficiency range as you posted. That would be tough to corroborate I bet.

But how do you explain your point with a t5 car then?
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Old 05-01-2009, 08:44 AM   #17
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I think its amusing that you are hanging onto that last little bit of "window" of difference.
I think it's amusing that you presume to be "amused" by anything that Vigge writes. I think the fact that you actually chose to use the word "amusing" is also amusing.

It's also amusing that you're so terribly arrogant while at the same time turn to write-ups by others, humanization of inanimate objects, and analogies, to explain something that shouldn't be a problem to explain and support, when considered correctly, because the effects of elevation are real. Everyone knows that they are.

Do you notice a trend in the people that you think are constantly "slamming" you? The people who you say are "slamming" and "smearing" you all have something in common. You're too busy exploding and going into attack mode whenever anyone writes anything that isn't a glowing review of your work, but honestly, you might do yourself a favor if you'd stop and consider that maybe you're wrong about some things that are pretty fundamental.

Do you think all these math/science/engineer type people that are 'bothering' you would continue to "slam" and "smear" you if you started making posts that were correct and true?

Is this a typo or not?
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The write-up re-states what I have been saying for years and what you said, a t7 car will increase boost/airmass to try and maintain the same power at eleveation.
Also, still waiting for those non-torque monster T7 dynos that you promised.
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Old 05-01-2009, 08:48 AM   #18
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Old 05-01-2009, 08:52 AM   #19
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Comparing T5 to T7 is like comparing apples to oranges in my opinion.

With T7 employing a MAF and MAP sensor that ECM is able to "know" exactly how much air is coming into the engine and can account for changes in air density much more effectively.

T5 using a MAP sensor only is a like a great big educated guess when it comes to air density. Hell, I've heard of some cars (not-saab) that are running the same speed density system getting very wigged out all due to the fact the volumetric efficiency of the engine was changed. This can be done by something as simple as changing cams. But the ECM has no way of measuring and accounting for the change so the ECM can't operate as effectively as it did when it was stock.

Think T7 knows how much air is coming in while T5 looks at baro. press., MAP, and IAT and guesses how much air is coming in.
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Old 05-01-2009, 08:52 AM   #20
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you're an engineer aren't you?
Who's that, me or John?

I am. JZW told me that he was once, but I don't know that to be true. His profile says "Facilities Specialist".

Ask Vigge what he does for a living.
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