I am once again confused about how the STi7/8 ecu handles altitude changes as regards boost control.

If I run 1.2bar relative boost pressure at 4000rpm at sea level (i.e. 2.2bar absolute) what will the car boost at -0.1atm below sea level pressure (1600m up)? Does the car just run the same absolute boost pressure of 2.2 bar (i.e. 1.3bar at 4000rpm) or does the ECU maintain the relative pressure?

rupert

..... have no idea on how the stock ECU compensate for that, IIRC it has a solenoid to switch from engine pressure reading to atmospheric pressure reading.

On a side note for alititude boost should decrease, at 1000 meters (~3280 ft.) above sea level ..... it should lower 0.1bar, and the higher you go this difference increases so for example here in Peru when you go to 4000 meters (~13123 ft.) we get almost 0.5bar less that you would get at sea level. Therefore I would expect to get a tad higher boost if your barometric pressure is below 100Kpa.

Carlos H.

Hi Carlos

I understand that the atm pressure decreases with altitude, but surely the ECU of the car is trying to acheive a certain boost target based on the desired boost programmed into the boost map? The question is, does the ECU try to achieve a relative boost pressure or an absolute boost pressure? If the ECU trys to achieve an absolute boost pressure ( I think the STi7/8 works this way ) then the car will have higher and higher relative boost at increasing altitude.

What will this do to the fueling and timing :-( .

rupert

It will try to deliver the target boost.

So yes, at 2000m your 1.2bar is actually a PR of 2.4 / 2.5................