So, I know that the factory ECU and GMS1 tunes supposedly "learn down" when you modify these cars, however I believe that at high altitude that is not the case.

Case in point -- Bandimere in Denver, CO is 5800ft above sea level and usually has a D/A of 7000-8000ft. However, there have been multiple cases of stock/GMS1 Cobalts running high 13 to low 14 second ETs with trap speeds @101-103 mph. Some have even modified their cars and are getting into the mid-13s and mid-100mph traps without any tuning.

Why do I think that the ECU isn't learning down? We all know the ECU architechture is designed around supplying the driver with the desired torque value up to a given point of timing and boost pressure, etc. At high altitude, it will always reach that threshold or limit before the car makes the desired power output.

So based off of that theory, anything someone does to make the delivery of that 20psi (stock tune) or 23psi (GMS1) more efficient (ie exhaust, intake, intercooler, etc) would actually improve the performance of the car and not cap it like the learn down feature does at lower altitude.

Has anyone here that lives at high altitude noticed anything to further substantiate this theory? I'm planning on doing a catless dp, intercooler, and charge pipes without any additional tuning late this summer and I'm going to see if my times improve.

I just know this - these cars f*ckin RUN at altitude. I know that turbo cars don't lose as much efficiency at altitude as N/A, but having the driver desired torque ECU architechture really makes a big difference. I've beaten countless F-Bodies and Mustangs. In fact I actually haven't lost to one yet. I've raced 2 new Camaros, both SS, and I was able to slowly pull away from each of them.

 

stock tune is 15 psi usually, and altitude wouldnt shut off any learn down, ur numbers ur getting are the same as any other stock cobalt. because ur so high up the computer is adjusting, i guess hitting the 20 psi ur talking about to keep the car at 260hp, 260tq.

 

The "learn down" feature is the same thing that's keeping your car boosting 20PSI at high altitude to try and make stock power.

You loose approximately 1PSI of atmospheric pressure for every 1000ft in elevation you climb over sea level. At sea level the car only needs to boost 14-15PSI to make stock power and any aftermarket parts that would increase power (without a tune) would eventually be corrected for over time. The 1/4 times you mentioned are right in line with what a bone stock TC would run at sea level.

At your altitude and above the car doesn't hit it's desired maximums so aftermarket parts only help get you there and aren't compensated for. That doesn't mean the system isn't there or is disabled though, it just takes more to make up for the lack of ambient atmospheric pressure and get to the power level someone at sea level would have.

 

Yeah....

 

This is exactly right.. a friend of mine just bought an SS in AZ and he said down there it only boosted about 13-14 then came up here to SL,UT (about 4500 feet) and boosted about 17-18 because the computer was compensating.

I am tuned, but even while running the stock tune (switchable) I hit as high as 20 sometimes..

 

When I was stock I'd hit 18-20 psi all the time. In fact I was convinced I had GMS1 and went around this forum parading the fact I got stock price on my car. I eventually learned its my altitude and learn down was actually learning up to keep my car at 260/260. So technically we still have learn down.

But I see your point, a friend of mine fully bolted stock tune just hit 13.6. I'm fully bolted and tuned and can't get in the 13s. Obviously I suck at launching but aside from that I can see your logic