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Discussion Starter · #1 ·
i was just wondering if anyone living in some of the higher elevations had installed a boost gauge? couple things i was thinking about, though they might have been discussed at times already.

anyhow, while glancing through the some speed3 stuff i found that on a dyno run, the stock MS3 was showing just over 13psi with their logging equipment at WOT at their 4000' facility. so the stock system seemed to not compensate for the change in altitude? when using an aftermarket coost controller, I BELIEVE (which is what i'm trying to figure out) that they work more on absolute pressure vs relative pressure.

so essentially you want to boost to an absolute pressure of 30.2 (at sea level, you want 15.5psi + 14.7atm) with a boost controller, and you go to a higher elevation....it's still gonna spool the turbo until abolute pressure is 30.2. if atm pressure is 1.8 lower (12.9 as COBB stated at their facility) than sea level, then the turbo would actually be spinning to 17.9psi to hit the boost you want. which is way out of it's efficiency.

now some cars (and my Haltech ECU can be setup that way) will figure out what atm pressure is at startup and adjust things from there. so you are only adding 15.5psi to the atm of 12.9 leaving an absolute pressure of only 28.4....but keeping the turbo well within it's efficiency.

so i guess my question is, have any of you guys looked into this, and possibly has anyone found that the car feels more lively when coming down to lower elevations? i don't have my ecu setup that way currently, and my haltech ecu was reading 1.5psi off of my gauges. so i'd hit my boost gov of the Hatlech at about 13 and change psi rather than 15psi....which sucked.

i guess my worry, is with all this talk of throwing on boost controllers (and i don't know if a MBC would work the same way?) some people at higher altitudes might be putting their little K04's at risk of some serious abuse. but would also account for any big jumps in power as well.

any thoughts?
 

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I'm only at 600 ft. above sea level. I know there are Colorado people that have posted on here. I'm interested to see what they have to say. MrTea, you're hypothesis as correct would rely on the asserted fact that the ECU does not adjust for ATMs, that of which I am unsure.
 

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I would be totally amazed if the ECU did not work off of absolute pressure, because otherwise it would never get the fuel mixture correct.
 

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Discussion Starter · #4 ·
the ecu will work fine however it's designed, that's not my worry. if my Haltech can do it, i'm sure the Mazda can do it 10 times better. if it did work from absolute pressure alone, then people in CO would stand to be killing their turbo's rather quickly i assume?
 

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Hypotheically, it could have some added wear on the turbo as the air coming in to the intake manifold is already much more pressurized by the atmosphere.

I think that the sensors would read the pressure along with the amount of air coming in.
 

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the ecu will work fine however it's designed, that's not my worry. if my Haltech can do it, i'm sure the Mazda can do it 10 times better. if it did work from absolute pressure alone, then people in CO would stand to be killing their turbo's rather quickly i assume?
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30lb absolute is 30lb at sea level or at 10,000 feet. The turbo would have to spin a little faster at altitude, but I would guess there is a margin built into the turbo...the difference couldn't be that great.

I could be wrong, but I have to believe the fuel injection works off of absolute manifold pressure. Contrary to popular belief, there is not less oxygen at altitude. There is just less atmospheric pressure while the percentage of oxygen remains constant. A total pressure in the manifold of 30psi would demand the same fuel flow regardless of altitude. A relative boost of 15.3psi at sea level (14.7+15.3=30) would need more fuel than a relative boost of 15.3 at altitude. You would be rich at altitude of lean at sea level, just like a carburetor without some kind of altitude compensation.

I'm guessing the wastegate opens on absolute pressure, but I don't know this for a fact. If it doesn't, there are power gains waiting waiting for us at altitude with a boost controller.
 
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