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This is a discussion on High Altitude Tuning within the High Altitude Tuning forums, part of the Engine Modifications category; I have an 09 Rex and was really disappointed with Cobb Stage1 91 Oct. The car felt very unresponsive... Perrin ...

  1. #61
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    I have an 09 Rex and was really disappointed with Cobb Stage1 91 Oct. The car felt very unresponsive... Perrin is sending me their brand new Stage1 today; I m very curious what they did on theirs.

    -WK


    Quote Originally Posted by 4x4speed View Post
    I have a 08 WRX and i want to go to stage one. I live in colorado, just really wondering how 08 WRX's have been doing on stage one in Colorado, i asked perrin since i am interested in buying the AC from them since i would get their stage 1 for free. Perrin said that they are in hard works on a High altitude map.

    So how does cobb's and Perrin's stage one does in colorado/high altitude?

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  3. #62
    Admiral Ackbar the 1st mycologist's Avatar
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    Some info I have gathered on High Elevation Tuning:

    2006 WRX Target Boost and Altitude [Archive] - NASIOC

    "06rexwagon03-16-2007, 11:57 AM
    Depending on barometric pressure, you will only see a fraction of what the targets are. I am at the same elevation as you, and with our barometric pressure, the ECU automatically targets ~12% reduction in boost, so about .88*15.6=13.8. You can target a higher boost to make it hit 15.6, but tightening your wastegate arm isn't the answer. The ECU WANTS to hit a reduced boost target and will do whatever it can to do it, including lowering your wastegate duty cycles depending on the turbo dynamics tables. All that being said, your car is doing what is supposed to do."


    Atmospheric pressure at altitude and boost compensation? [Archive] - NASIOC

    "Dis-regarding efficiency and temps., I could up the boost more than at sea-level to compensate for the reduction of ~2psi in ambient pressure. BUT, the stock TD04 turbo is not the ideal partner for this excercise as it's already too small.

    Stock boost pressure appears to be similar to sea-level dweller's reports. ~13-14psi max. So, I would say that the stock ECU does compensate (somewhat) for altitude.

    The problem arrives (I think) when you start at, say, 6000ft and then drive up the nearest mountain at, say, 14000ft. If you're using the stock ECU boost control, the system will not choke and your max boost pressure will be ~11psi.

    If, however, you use some other method (TXS Unichip ABC, MBC, EBC, etc). then you will very likely cause a CEL for overboost... I don't really know why, but it happens to me and others I know wih WRX's..."



    legacycentral bbs :: View topic - Higher elevation, same boost level

    Note this is a legacy, and it seems the turbo has more of a buffer based on the discussion.

    openecu.org • View topic - Barometric compensation adjusted to climate

    "I believe on Subarus there is no direct barometric pressure to timing correction. IAT, yes. Baro compensates against boost limit as well. "



    "MAF – Mass Air Flow ‘’‘– The MAF consists of a conglomeration of many different sensors that when put together in an electrical equation, is “fairly” accurate. The next section of this guide focuses on just the principals of MAF Sensor principals. This is a rather important part to any DSM/Subaru auto for proper fuel burn. They are; Barometric Pressure Sensor (integral part of the MAF) – This sensor measures atmospheric pressure, density and for elevation."




    Some have messed with the barometric pressure compensation map in Evo's. "The Barometric Pressure Compensation map is used to keep the cars fuel AFR is properly maintained by measuring air pressure and density. Adjusting this map has no keen advantage over performance, and is usually adjusted to geographical location based on elevation (USDM/JDM/EDM)."

    Oh and if the OP ever comes back - look for the pirates sig, they understand what is going on at high elevation much better than us (/thread).

    Diminishing Boost at High Altitude - ClubWRX Forum - Subaru Impreza WRX and STi Community and Forums

    (a high elevation specific post)
    "The low rpm behavior of a turbo as far as boost onset is greatly affected by how the boost controller is set. If I knew I was not going to get into a prolonged high boost situation in a higher gear. I could make the stock turbo hit so hard if almost felt like N2O.

    In situations like rallyx you can get away with that because your never on the loud peddle for more than a couple seconds at a time. ON the street that same boost controller setting would result in severe overboost, so the stock boost controller could very well be a limiting factor for him."


    "limits of turbo

    --------------------------------------------------------------------------------

    I tried some expeiments when I first got my WRX and found that even if I crank the boost controller to a ridiculous number the turbo will run out of breath at very high altitude.

    With an EBC set for very high boost I could not reach 1 kg/cm^2 boost at 13,600 ft altitude. The pressure ratio is just too high for the turbo, you push it way out of its effeciency range and it becomes a circular feed back.

    Hot air out of turbo, reduces mass flow even though your holding boost. Lower mass flow means less exhaust gas mass flow, less power to drive turbo.

    At the same time, as you climb the inlet pressure on the compressor keeps falling so to hold the same boost the turbo has to actually operate at a higher pressure ratio. Which requires more power from the hot side tubine.

    At some point you either bump into the max rpm of the compressor, or the max flow limit. Your moving a lot of volume but it is hot and not much actual mass, so after intercooling, less boost.


    Anyway thats my experience.

    Larry

    boost is good -- but!!!

    --------------------------------------------------------------------------------

    There are two things I think that you need to realize about altitude effects and turbos.

    First the turbo doesn't know what altitude it is at or what engine it is connected to. All it knows is the density of the gas at its inlet, and the pressure ratio you are asking it to work at, and indirectly it knows the engine size because the engine can only accept so much flow at a given rpm with a given engine displacement.

    Second is that the engines actual power output is a function of the absolute manifold pressure not the boost. You have to remember to consider the effect of the drop in local air pressure too.

    What that means for us is that the stock WRX 2 liter at about 4500 - 5000 rpm wants to accept the right amount of flow to put the stock turbo in the sweet spot of its compressor map. At these mid range rpms you can successfully use all the pressure capability of the turbo. If you ask it to, it can deliver almost 26 psi boost at sea level at this rpm point. Thats a pressure ratio of just short of 2.8:1. Here at altitude you run the same pressure ratio and because the inlet pressure is lower you only get a fraction of that boost.

    For example the standard pressure here at 6000 ft altitude is 11.78 psi, so that same 2.78 :1 pressure ratio gives a boost of 20.9 psi, but because the local actual air pressure is only 11.78 psi the total absolute pressure in the manifold is 32.7 psi, compared to the absolute manifold pressure of 40.8 psi at sea level. To get an absolute manifold pressure of 32.7 at sea level you only need to run a 2.22:1 pressure ratio (which means cooler out let temps) or a boost of 17.9 psi.

    This is why you can never (practically speaking) completely negate altitude effects. If you try by running higher boost your running the turbo at a higher pressure ratio and it will almost always produce less actual mass flow.

    Due to the higher pressure ratios you need to run at altitude, turbos have to spin faster to make the boost, so lag is worse (takes longer to spin up the turbo to the higher rpm).

    I have run pretty high boost on the stock turbo up here (18.5 psi peak) to get the max out of the stock configuration. But this is only useful in the lower 2/3rds of the rpm range.

    I know that the high rpm end of the power band is pretty useless as the turbo just can't produce enough flow at that pressure ratio. I counter that by using an agressive waste gate duty cycle on my boost controller to get boost just as fast as I can and seldom take the engine past about 6000 rpm.

    Larry"

    Note that is for a 2l.
    Last edited by mycologist; 01-27-2009 at 12:06 PM.
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  4. #63
    Wrinklechops
    And I was so excited to put this Cobb AP stage 1 on my '05 WRX and tackle the back and forth drive from Denver to say, Avon....the I-70 mountain passes drive I call it... And I was thinking the AP giving me 25 more hp and torque and raising my boost that I'd be flying up the mountains...but I am afraid my engine is going to get starved for oxygen more than it already does at 12,000ft lol

  5. #64
    UnBanned Sinister's Avatar
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    Quote Originally Posted by mycologist View Post
    Some info I have gathered on High Elevation Tuning
    I really wish you would've reposted this in the thread about me getting tuned! It's interesting information!
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    Quote Originally Posted by lundholm08 View Post
    And I was so excited to put this Cobb AP stage 1 on my '05 WRX and tackle the back and forth drive from Denver to say, Avon....the I-70 mountain passes drive I call it... And I was thinking the AP giving me 25 more hp and torque and raising my boost that I'd be flying up the mountains...but I am afraid my engine is going to get starved for oxygen more than it already does at 12,000ft lol
    You're fine. You may not get the gains you'd like, but you never will here at altitude. You'll be safe though! And like I said, any time you'd like, I'm up for a drive, so you can see if what I've done, is what you'd like to do.

    First off, COBB is in salt lake city, so their maps are safe at altitude.

    2ndly, your engine uses the MAP sensor to be able to determine barometric pressure. Since you are getting the COBB OTS map for Stage one, you'll be fine, and the ECU will make compensations. If you were tuned and had a bad tuner that doesn't know about barometric compensations, then you'd have a pretty big problem. That's one thing that happened to me with my first protune. The guy didn't adj for baro compensations, and I drove from here in colorado down to california, and I was hitting boost cut like it was cool. Now with my new map, the tuner set up the compensations so I could "travel from death valley to the top of mt evans safely" (his words exactly)
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    Quote Originally Posted by Sinister View Post
    I really wish you would've reposted this in the thread about me getting tuned! It's interesting information!

    Thanks. I was afriad that would be a bit too much to repost though. I'm at 3500' and head above 5K' often, so I have looked into it a bit.
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  8. #67
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    Quote Originally Posted by mycologist View Post
    Thanks. I was afriad that would be a bit too much to repost though. I'm at 3500' and head above 5K' often, so I have looked into it a bit.
    I really wish I could quote exactly what my tuner explained to me... It was a lot of information, but he showed me the barometric tables that he was adjusting, and explained why turbo-charged engines are more efficient than N/A at altitude, but the turbo it's self becomes less efficient.

    It was interesting info, but sitting in the back seat for a 3hr tuning session, you learn a lot, and remember a little!
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  9. #68
    Wrinklechops
    Quote Originally Posted by MountainMotor View Post
    Anyone up here @ 8150 with me?


    Me, in Avon you have boost issues too? Someone told me boost diminishes approx 1psi for every 3500ft so that's like a 2.31 drop for us!

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    Quote Originally Posted by lundholm08 View Post
    Me, in Avon you have boost issues too? Someone told me boost diminishes approx 1psi for every 3500ft so that's like a 2.31 drop for us!
    I was just going to direct you here ...
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    Quote Originally Posted by lundholm08 View Post
    Me, in Avon you have boost issues too? Someone told me boost diminishes approx 1psi for every 3500ft so that's like a 2.31 drop for us!

    That was off the top of my head. Here is the source, the car discussed is Cobb stage II -

    2006 WRX Target Boost and Altitude [Archive] - NASIOC
    "Airboy03-16-2007, 01:30 PM
    The atmospheric pressure compensation for the '06 WRX is ~-13% at 12.2psi (5000ft). However, this value is applied to the boost target in absolute pressure. So, Boost target of 15psi gauge is actually stored in the ECU as 29.7psi (actual unit is mmHg but anyways). At 5000ft elevation, the target becomes 25.9psi MAP. Subtracting atmospheric pressure of 12.2psi and you get 13.7psi gauge pressure.

    http://img301.imageshack.us/img301/2...nsationrn2.jpg
    "
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  12. #71
    Wrinklechops
    Quote Originally Posted by mycologist View Post
    That was off the top of my head. Here is the source, the car discussed is Cobb stage II -

    2006 WRX Target Boost and Altitude [Archive] - NASIOC
    "Airboy03-16-2007, 01:30 PM
    The atmospheric pressure compensation for the '06 WRX is ~-13% at 12.2psi (5000ft). However, this value is applied to the boost target in absolute pressure. So, Boost target of 15psi gauge is actually stored in the ECU as 29.7psi (actual unit is mmHg but anyways). At 5000ft elevation, the target becomes 25.9psi MAP. Subtracting atmospheric pressure of 12.2psi and you get 13.7psi gauge pressure.

    http://img301.imageshack.us/img301/2...nsationrn2.jpg
    "
    So, in laymans terms, if my target boost was 16.5 (+/- .7) according to Cobb, and I was hitting 13.64, 13.93... but the target boost should really be around 14-ish at 8000ft elevation, I am actually on target?! Good news...maybe....lol

  13. #72
    Wrinklechops
    Quote Originally Posted by wrx686 View Post
    Yeah its really High. I have already tried it but nothing changed. oh well

    Does anyone live at or around this altitude?

    I know this is ancient, but I like at 8000ft also, here in Avon. I just flashed to Stage 2 and can only hit upwards of 13.64psi. I'm going to try the HWG map as well.

  14. #73
    Admiral Ackbar the 1st mycologist's Avatar
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    Quote Originally Posted by lundholm08 View Post
    So, in laymans terms, if my target boost was 16.5 (+/- .7) according to Cobb, and I was hitting 13.64, 13.93... but the target boost should really be around 14-ish at 8000ft elevation, I am actually on target?! Good news...maybe....lol
    Atmospheric pressure at 8000' is 10.9, or around 21% reduction

    16.5psi guage + 14.7 (atmospheric at sea level) = 31.2 MAP

    31.2 * .79 = 24.6 MAP

    24.6 - 10.9 = 13.7 gauge

    You are hitting your boost target so just quit worrying about it until you can get a high elevation tune.
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    "The stitch is lost unless the thread is knotted." - Italian proverb

  15. #74
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    Quote Originally Posted by lundholm08 View Post
    So, in laymans terms, if my target boost was 16.5 (+/- .7) according to Cobb, and I was hitting 13.64, 13.93... but the target boost should really be around 14-ish at 8000ft elevation, I am actually on target?! Good news...maybe....lol
    It can be compensated for with a tune. Well... somewhat.

    The barometric pressure, combined with the pressure of the turbo, minus the pressure loss between the turbo and the intake manifold... that right there is the number that matters. The manifold pressure is directly related to how much air and fuel is injected into the chambers.

    But at the same time, we also can't achieve as much boost because the turbo has to work harder to create higher pressures. The higher the barometric pressure (atmospheric pressure...) the easier it is for the turbo to compress into useable output. That's because gaseous pressure isn't linear.

    So, because of the above 2 statements... we experience pressure loss at altitude, and we aren't able to produce the same amount of power as lower altitudes at the same boost.

    So we can crank up the boost, but that doesn't mean that it'll be efficient enough to produce as much power as was possible at lower boost levels.





    On a side not, I'm not doing much during the days this weekend... I may be working around the house, but feel free to give me a ring, I'll let you ride around in my car to see if it's the same sounds you're hearing. I'm guessing that the "whining" you're hearing is the impact of air on the impeller wheel.
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  16. #75
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    Seems to be a big problem up here in the C-O.lol.I just came from texas and my 04 WRX is sucking.It's like my car don't even want to move on go.Anyways should i get a tune? How much we looking at.I had one guy say about 500.Would it be worth it cause im here only for a few years so im looking at possible benefits when returning to lower altitudes or if i would have to re-tune there also.Any other suggestions?

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