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I'm at 4900 ft. - close to the Cobb Tuning shop altitude.

Does anyone have any experience w/ Cobb's Stage2 93 HWG map for 2.0L WRXs (the one for 'people who have trouble reaching target boost')?.

Posting here because I'm guessing the altitude plays into the max boost levels. And because no one ever posts here, so I figured what the heck...

P.S. yes I've searched
 

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I live at 3500 and get up to 5000 regularly. I'm very interested in whether any better information gets posted here, but my understanding is that you don't want to trick the car into running normal boost levels. The ECU lowers target boost (independant of the map) for a reason, I just never really got why. Most maps I've seen discussed that are tuned specifically to high elevations have less boost as well. Mayhaps it is because your turbo has to work harder to move enough of the thin air to hit the target?? :confused:
 

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Maybe it's because the ECU has to take in more air to achieve that same level of boost (since the air is less dense at the higher altitude). And it can't safely accommodate the higher air ratio w/ stock fuel delivery (?) Although, the air is thinner, so wouldn't the MAF sensor figure that out? :sadwave:
 

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I just re-read the end of your post and realized you came to the same conclusion about the thinner air making the turbo work harder... That definitely seems like the most logical explanation at this point.

Seems like somebody somewhere has to have addressed this. Maybe I'll search NastySock.
 

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Maybe it's because the ECU has to take in more air to achieve that same level of boost (since the air is less dense at the higher altitude). And it can't safely accommodate the higher air ratio w/ stock fuel delivery (?) Although, the air is thinner, so wouldn't the MAF sensor figure that out? :sadwave:
I forget how pressure is sensed, but yes, it does, and many people say you can run lower octane as well. So my thoughts lean toward the turbo itself getting too hot. :confused:
 

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Ev8siv3 had real bad problems trying to get his map to work up here in SLC. The problem is ubundant again know that the weather has changed. I need to seek help once again because my KC is going all over the place and I am over boosting again.

Have you tryed to adjust (tighten) your Waste Gate arm at all? What happens is the stock WG system sucks and gets maxed out way to easily. I don't know if you can adjust the arm with a cobb map though:confused:
 

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Ev8siv3 had real bad problems trying to get his map to work up here in SLC. The problem is ubundant again know that the weather has changed. I need to seek help once again because my KC is going all over the place and I am over boosting again.

Have you tryed to adjust (tighten) your Waste Gate arm at all? What happens is the stock WG system sucks and gets maxed out way to easily. I don't know if you can adjust the arm with a cobb map though:confused:
I'm having a real hard time following which of your cars is doing what. Are you saying that either you or your buddy are overboosting because of elevation? Or did you pinch your wastegate arm down to achieve target boost even though your ECU is supposed to be pulling boost for your elevation?

The cobb map HWG is for high waste gate or something, and it increases boost when below their target IIRC. The boost will overshoot briefly, but that isn't the issue. Manually adjusting the wastegate to force higher boost than what is mapped for - that is the map value minus the correction employed by the ECU for the elevation - is not sounding like a good idea to me. IIRC you loose around a pound per 3500' or something in that general range. I can't see arbitrarily undoing this correction as a good idea.
 

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I'm having a real hard time following which of your cars is doing what. Are you saying that either you or your buddy are over boosting because of elevation? Or did you pinch your waste gate arm down to achieve target boost even though your ECU is supposed to be pulling boost for your elevation?

The Cobb map HWG is for high waste gate or something, and it increases boost when below their target IIRC. The boost will overshoot briefly, but that isn't the issue. Manually adjusting the wastegate to force higher boost than what is mapped for - that is the map value minus the correction employed by the ECU for the elevation - is not sounding like a good idea to me. IIRC you loose around a pound per 3500' or something in that general range. I can't see arbitrarily undoing this correction as a good idea.
That's not what I meant. I think cobb and enginuity use different lingo to describe the Waste Gate function of the ECU.

I was wondering if buy tightening the WG arm he could achieve the target boost with more easy. I didn't mean to go out of the maps range, rather help the WG achieve the boost it is trying to make. The problem isn't that the air is too thin and the turbo cannot make the boost. It is that the Boost Control system on the car maxes it self out because it is restrictive. That is why people use a GM BCS because it is a much more effective system of controlling the boost.
 

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Cobb is located in Utah, so I would imagine they have maps for High Altitude conditions. Give them a call.
 

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That's not what I meant. I think cobb and enginuity use different lingo to describe the Waste Gate function of the ECU.

I was wondering if buy tightening the WG arm he could achieve the target boost with more easy. I didn't mean to go out of the maps range, rather help the WG achieve the boost it is trying to make. The problem isn't that the air is too thin and the turbo cannot make the boost. It is that the Boost Control system on the car maxes it self out because it is restrictive. That is why people use a GM BCS because it is a much more effective system of controlling the boost.
OK, I'm just trying to get to the nub of this simply because I want to understand what is really going on.

I thought the GM BCS was to help with the normal overshoot, undershoot, then stabilize that people get. My point is that the map's range is tempered by the ECU, so you will not see what is published as normal boost target as you get into higher elevations. E.g. I hit 15.3 with the normal 93 octane stage II Cobb map, not the 16.5 or whatever is the actual target. This is due to the ECU corrections pulling boost. I still think this is because the turbo has to work harder to hit the boost target (which yes it can do). So when people say the stock turbo is maxed out at ..., you have to subtract the correction for altitude. The restriction in the BCS leads to overboosting in later models (boost creep), so I don't see how it will cause underboosting. Cranking down the arm or changing the pill are ways to achieve target boost if your not hitting it at sea level IMHO, but you are basically boycotting the system as I understand it. If this is incorrect than I am anxious to hear the real story.
 

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From what I understand and seen is that the stock BCS is crap. I don't know how to explain it but I'll try. The system is holding the boost it by keeping the WG closed. As the boost increases the amount of work the BCS does to keep the waste gate closed does as well. At a certain point (psi) the BCS is doing all the work it can and still not hitting it's target boost. It maxes the system out. Ev8siv3 saw this on my car and said that it was the altitude. With the after market BCS the system does not have to work nearly as hard to make the same boost and controls it better.
 

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Ok, here is the backup:

http://forums.nasioc.com/forums/archive/index.php/t-1222856.html

"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."


http://forums.nasioc.com/forums/archive/index.php/t-145736.html

"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..."



http://bbs.legacycentral.org/viewtopic.php?p=178751&sid=5292ab72b8a0a3a9615bb6c769a9fbf7

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

http://forums.openecu.org/viewtopic.php?p=7624&sid=697c962ca9ca51b2d54c93b0068aa0cf

"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."


Ok, so lets make a high elevation map - but why. To target higher boost than we should be? The pressure compensation table is already doing its job basically correctly. To set a lower boost target - again, the pressure compensation table is already doing its job basically correctly.

Here is the only why I can think of "Wastegate Duty Cycle Barometric Compensation (%, 6 load x 4 rpm)": Seems like the only thing to optimize. It is listed as available to adjust with a protuner, but not modified in any maps I have seen: It certainly isn't part of any OTS maps I have heard of.


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)."
 

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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).

http://www.clubwrx.net/forums/showthread.php?t=16993

(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

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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!!!

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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.
 

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Wow that's a lot of good info; especially in the linked thread - I'll wade through it in the next couple days. Thanks for digging that up. :thumbup:
 
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Wow that's a lot of good info; especially in the linked thread - I'll wade through it in the next couple days. Thanks for digging that up. :thumbup:
Hey wait3, if you're still around... any feedback on what you ended up doing? I'm at about 6000-7000ft and thinking about running the Cobb HWG map because with the regular Stage 1 I'm only getting like 12psi...
I will be moving back down to Denver (5000+ft) here soon though...
 
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