ipozestu

iTrader: (18)

Every time I go to Tahoe, I get the boost withdrawl syndrone. I push maybe 10-11lbs. Would a manual boost controller hurt anything in this case if I were to turn to boost back up to 14lbs or would increasing boost manually at elevation have to same effects as increasing boost at sea level? What's the deal here?

BoxerRumble

iTrader: (7)

I think this was covered way back then. From what I know, since the elevation is a lot higher..the air is thinner. It's like if you tried to boil water, it would take longer. Since air is thinner, you need more air in the engine, so when the turbo compresses the air, it needs more than usual to make the same amount at sea level. I'm just talking outta my *** right now, someone correct me, but this is how I see it is. Of course, I have no idea what im talking about =D

HomerJay

iTrader: (3)

No boiling water takes less time and lower temps becuase of reduced air pressure.

edit: Even if you increase boost all the way to 14psi's you aren't going to make the same HP as sea level since there is less oxygen. You're better off remapping ecu for those conditions. This will probably make you run a little rich, since more fuel will be used to compensate for the lack of oxygen.

mattsn0w

iTrader: (23)

I would say don't **** with it. I think it is safe to say it happens on all of our cars.

MVWRX

iTrader: (1)

...yeah, things take longer to get cooked in boiling water at elevation but it takes shorter to get the water to boil...

bluwrxwgn

iTrader: (3)

I have always noticed this at elevation. The turbo just takes forever to spool because the air is thinner, but when it does it comes on like a ton of bricks.

Bismarck

iTrader: (3)

This is incorrect. If you remap the ECU for a lower air pressure, the ECU should be using LESS fuel. The reason you are losing power is because the mixture is too rich already - more fuel will NOT be added to compensate for a lack of oxygen, in fact quite the opposite should occur. To generate equivalent power with less oxygen, you need LESS fuel. The engine must be leaned out in order to perform at altitude near what it does at sea level. This is exactly why air-cooled (or more appropriately fuel-cooled) reciprocating engines in aircraft have a mixture control. The mixture can be leaned out as altitude increases, air pressure drops and there is less oxygen available for combustion.

To more appropriately address the topic of this thread - that being lower boost levels at altitude - simply put, the air is less dense at higher altitudes than it is at sea level. Therefore, the compressor has less material to work with and subsequently produces less compressed air, i.e. lower boost pressure. Modern electronic fuel injection systems normally are capable of compensating for this on normally aspirated motors. They simply lean out the mixture as the air pressure decreases. However, unless you have a variable blade pitch on your turbocharger compressor wheel, it will not perform the same at altitude as it does at sea level. It is a fixed mechanical device that has no way of adjusting itself to changes in ambient temperature or pressure.

As to the question of the manual boost controller... As I said, if you spin the turbo faster (i.e. keep the wastegate closed longer) you can probably achieve more boost. However, you'll need to readjust it before descending to lower altitudes, otherwise you're going to overboost when the air gets more dense. I'd wager that a stock car would still achieve stock boost levels, as the ECU would be in control of the boost control solenoid and automatically keep the wastegate shut longer to maintain normal driving status. But seeing as I have no real-world experience with driving a stock WRX at altitude, that's just speculation on my part.


-Bis

ipozestu

iTrader: (18)

Bis that is along the lines I was getting at. By forcing the waste gate closed longer I would be able to increase boost, in turn I would be requiring the turbo to compensate, forcing more rpm. Would it be correct to say that a turbo at altitude manually controlled to 14lbs would have to spin the same rpm as a turbo at sea level manully controlled to 18-19lbs? How much boost is the Stocker good for? Boost limitations are related to turbo RPM limitations, Correct?

scottzg

I dont have a turbo sube, but i believe that the ecu checks the pressure sensor on startup to see what ambient air pressure is. When you drive up the hill, it can't check ambient pressure, so you lose your boost. So, if you turn the car of and on (you could do it while rolling) it will recheck ambient pressure.

MVWRX

iTrader: (1)

Don't turn your car off and on while rolling, please. Not only is it illegal, but it makes the brakes work weird, there's no power steering, and you don't have the ability to accelerate to avoid another car or something.

ipozestu

iTrader: (18)

Wrong!!!! This is not the case. The ECU really doesn't care about barometric pressure. This is a question about possibly damaging the turbo due to excessive RPM form manually controlling boost to 14psi at 6200 ft. Ya see without manually controlling the boost on a stock turbo you get about 10 or 11lbs at 6200 ft. If you were to manually increase boost to 14 psi @ 6200 ft would this be the same as manually increasing boost to 18-19lbs @ sea level. When I say same I am speaking of conditions.

ipozestu

iTrader: (18)

Did you really think I'd turn my car off and on while I was driving???? LOL

Bismarck

iTrader: (3)

You're on the right track. The turbocharger actually doesn't "compensate" per se, it merely spins faster as less exhaust gas is being diverted through the wastegate. Without more data (air pressures are the varying altitudes, compressor wheel maps, etc), it's tough to make a call on what the equivalents would be. I DO know that leaving it set where you're seeing 14psi @ 6200 and driving back down to sea level would probably be rather detrimental to the life of your motor. I believe the stock turbo is good for about 16 or 17 psi before it starts getting too far outside its efficiency range to be of any use, but don't quote me on that.

Heh now you're getting a little outside my area of expertise. My knowledge of turbochargers and how it all works gets into that "knows enough to be dangerous" range here. As I understand it, boost limitations are a factor of many different things, from compressor wheel geometry to maximum turbine RPM to pressure and flow rates.

I do want to address a point mentioned above about pressure readings. As far as I can tell, there are 2 sensors that the WRX has to get an idea of what the outside air looks like - MAF and MAP. Between these two sensors, that's how the ECU determines how much fuel to use in the mixture to maintain the proper AFR. There is no "ambient air pressure sensor" or anything like that. All the calculations are based on data from these two sensors, although I have no clue what forumlae or algorithms are used internally to generate the appropriate responses.


-Bis

Bismarck

iTrader: (3)

BTW, you might want to drop by one of the Midwest / Colorado forums here or on Nasioc and ask them about this issue and what can be done about it. The CO guys and girls spend their entire lives at 5000 feet, so they'll probably have better real-world information than I do.


-Bis

scottzg

right. what im saying is that if you turn on your car at 6200 feet, you should get full boost, as the ecu will have seen the barometric pressure and compensated.

Of course, since i dont have a wrx, im totally talking out of my ear.