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It has been a few weeks since the AP stage one tune has set it. I took a reading the other day and in both 4th 5 th and 6th I hit 17.0...HOWEVER this was up in the mountains near stanley where the alt was probably about 4500 and up, and the temp outside was a chilly 40 degrees. How does temp and alt affect boost and A/F ratios? Higher alt richens you up right?
 

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The ECU adjusts for all the parameters, including AFR's, but at some point the turbo won't hold target boost. I think I've seen guys in Colorado say that altitude is somewhere near 6.5K elevation. Regardless, you loose power as you go due to the drop in ambient pressure, though not as bad that suffered by NA cars.
 

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IDAHOSTI said:
It has been a few weeks since the AP stage one tune has set it. I took a reading the other day and in both 4th 5 th and 6th I hit 17.0...HOWEVER this was up in the mountains near stanley where the alt was probably about 4500 and up, and the temp outside was a chilly 40 degrees. How does temp and alt affect boost and A/F ratios? Higher alt richens you up right?
Actually in my experience the oppositte is usually true but it all depends on how the car is tuned and I don't have any first hand experience with Cobbs maps with the Access* products.

It usually leans out actually. The reason is the higher you go up the less air you are pumping through the engine since you are losing atmospheric pressure the higher you go up. Typically it's about 1.1psi loss of atmospheric pressure for every 2000ft you go up. So at 4500ft you are probably seeing around 14.7 - 2.5 = 12.2psi atmosperhic. So even if your turbo is able to hit the same target boost levels at higher altitude (which can happen in the midrange but is VERY rare the closer you get to redline) then you are flowing less air through the engine. This less airflow is also compacted by the fact you are spinning your turbo harder to get that same boost (or less boost even - higher PRs) = higher turbine RPMs = higher EGBP = less airflow through the engine.

So the ECU is seeing less air flowing past the MAF = lower load point which typcially means more aggressive timing and leaner afrs but this is where it varies to the tune the tuner puts on the car.

Overall this is a bit of a high overview semi-simplification and there are quite a bit of variables involved. The easist thing to do is get yourself a wideband. Hook it up at sea level and then do some driving. Then go up to 4500ft and do the same type of driving and see what you see. I remember when I used to live in Colorado Springs (6000ft asl) and was tuning my Link ECU on my 02 WRX with a wideband I would drive up to Pikes Peak (14,000+ ft asl) to tune out the lower load ranges (idle and part throttle mostly). It was a lot of fun and a very good learning experience. I suggest you try it if you have the means ;).

One nice easy general rule-of-thumb I learned with my WRX going from Pikes Peak down to sea level is as the higher you go the harder it is to get the car to detonate since you just don't have the air to create the boost pressure. At 6000ft asl on my 02 WRX with the Link and/or UTEC I could get away with 12.5:1 afrs, 16psi relative boost, and pretty aggressive timing on a 18G turbo. But at sea level running even 10.5:1 afrs, 16psi and conservative timing in Phoenix I would knock a bit.

hth a little.
 

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Interesting, and I wonder if your AFR change is due to the Link's inability to compensate. The reason I ask is I've thrown on a wideband where I live (4K elevation) and the AFR's are the same (measuring variability excluded) as they were at the tuner's shop (roughly sea-level) - and this is at 24.5psi of boost both places (GT30). It certainly makes less power though, for the reason both of us have explained. I haven't logged timing or other values, however, so you may dead right in that regard.

One question: is the gas in Colorado different from AZ? 10.5:1 AFR seems awfully rich to knock with conservative timing unless you're putting 91 thru it, and you weren't before.
 

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Flycaster said:
One question: is the gas in Colorado different from AZ? 10.5:1 AFR seems awfully rich to knock with conservative timing unless you're putting 91 thru it, and you weren't before.
I am not sure. I know when I was in Phoenix the Mobil1 91 octane was much more knock prone than the Chevron 91 octane.

Here in Colorado I usually (luckily) have lived close to one of the FEW stations that sell 93 octane.

With the Link I was actually able to see what load cell I was in and at sea level i could/would hit load points that I just could not hit at higher altitude therefore I couldn't tune for those load zones. And even when I could the tune was different enough given the different operation of the turbo (different PRs). And I am talking smaller turbos like the VF22 and TD05H-18G compared to a nice GT30 setup (assuming EWG) which has a lot more 'reserve' on the compressor map for different PRs and different elevations ;).
 
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