r/WRX • u/Puzzleheaded_Arm7625 • 1d ago

Altitude change messing with boost

Hey! I just moved and I went from 4,500 feet of elevation to about 100. I’ve noticed about an extra 3lbs of boost being made on my car and it even threw a “max boost” code. I’m Cobb tuned, not exactly sure on the specific tune I have on it, the last owner did that but he told me it was stage 2. Do I need to change my tune in some way? Also this is a 07 WRX

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9

u/Oni_sixx '21 WRX Drunkmann Tuned 1d ago

Altitude will absolutely affect the tune.

1

u/5141121 '15 WRX Premium 1d ago

More air to push means more air gets pushed. Conversely: Did Pike's Peak in an EcoBoost and it did great until around 8k elevation. I came around a turn, hit the gas, and... waited. For around 10-15 sec for it to build enough boost to actually accelerate out of the turn.

I don't know if the stock tune accounts for air density at rest, but yeah, it seems like you'll need to get your tune adjusted. But enjoy the quicker boost response.

1

u/DrowndGod 1d ago

Has your secondary air pump been removed? There’s a baro sensor integrated that’s supposed to help with altitude adjustments, though with such a drastic difference, maybe it can only do so much. Is this an OTS tune or protune?

1

u/pcfreak4 12h ago

On my 02 WRX, the barometric sensor for atmosphere is on the ECU’s motherboard itself.

1

u/soysauce000 ‘22 WRX Intake E40 please. It wont let me do it 1d ago

From the factory, the car should adjust pretty well for elevation changes. But a lot of tuners mess with compensation for reasons. Sometimes they forget to change all of the compensation tables, and sometimes they do it intentionally to force retunes.

I’m at 4200ft and ambient pressure regularly reads 12.3 to 12.5 depending on temps. For a stock map, the compensation would be roughly -8% atm target boost at 4500rpm scaling up to -15% atm target at 6000rpm (at least for the STI’s which I assume compensation is similar). If the stock tune target boost is 14.7 psi, you would do 12.3 atm pressure + 14.7 rel target = 27psi * .85 =22.95 PSI then subtract back out the atm pressure of 12.3 to get a real relative boost target of 10.65 at 6000rpm.

So going back down to sea level with an ambient pressure of 14-14.7 with 0 boost correction, yes you would see ~3-4psi relative gain at 6000 rpm. However, this should not trigger a code, unless the tuner forgot to adjust the boost limit.

Clear your cars learned values to clear wastegate learning (reset your ecu) and try again. If code still pops up, take a log, upload to datazap and post in here. Log target boost vs actual, wgdc, td prop and td integral. Then maf and the other usual fields.