Shep 1.8T

however, the reality is the kits on the market are pushing the turbos flow capability to near the limit already. Coupled with a MAF who's values are scaled around sea level figures as well as an altitude sensor that reduces fuel use to compensate for less air = same/negligble difference to the losses on NA cars at the same altitude.

Sure you can theoretically tune/etc around it. However, telling the guy who is buying an off the shelf kit tuned at sea level that he is only going to see a 3~5 % loss is simply not accurate.

Not only that but I don't know of any kit on any market that isn't pushing the envolope in terms of using almost all the flow capacity of the turbo, otherwise what would be the point?

ULTRA4

You can have 3-5% variance between cars alone.

downindenver

1) thinner atmosphere = lower atmospheric pressure (this the basic principle used for altimeters in airplanes)

2) turbos/superchargers produce positive pressure. They keep producing pressure to an specified PSI (depending on the limiting device - software, wastegate spring, etc). Additional pressure is bled off.

A turbo is less effective at altitude, meaning it takes more time to reach the same PSI. At a given PSI, you'll get the same density regardless -- unless you think the air is fundamentally a different physical composition (other than pressure) at sea level vs altitude. But in the end, if you reach the max boost (say, 1 ATM or 14.7 PSI) you're pushing the same amount of air regardless of altitude. Thus the use of turbos in airplanes.

There *are* two ways to measure boost -- absolute and relative. Not sure what's used on most cars...anyone? With absolute, you'll never see any 'peak' power loss. With relative, you will, but it still won't be as bad as a N/A car.

Don't believe me? Talk to borg warner...<ul><li><a href="http://www.turbodriven.com/en/turbofacts/advantages.asp">Borg Warner - Read 4th bullet</a></li></ul>

ULTRA4

as well as conditions, a generalization or average of tuning if you will. There are a decent amount of adjustments that can be made to account for individual car/condition idiosyncrasies within the limits of said kit. A properly tuned and even stock car WILL adjust to barometric pressure differences based on MAP readings. This will result in an increase in boost or decrease in fuel to achieve the proper A/F and Torque output. If this were not the case airplanes would still be N/A to reduce the number of moving parts and increase reliability. If you do not agree it is your right and I will allow you to be just that. Merry Christmas...J/K.

Shep 1.8T

right, but not a 12 to 17 % variance, which is my point.

ULTRA4

in the form of actual versus requested boost in millibars. You have to subtract an atmosphere from the readings to realize the amount of boost. In order to find the relative amount you would need a bar reading at different alt which is not static given atmospheric conditions.

Shep 1.8T

prior to 00 model year there is no MAP sensor, and no requested versus actual for boost.

ULTRA4

All are acceptable variances but they add up when you compare numbers vs numbers between cars at different times and places. CAPS cannot even be compared unless they are done same time same place. The only true comparison is if these are done(dyno/CAPS) at the same place or dyno and conditions on the same vehicle.

ULTRA4

The car in question is a B6

Shep 1.8T

if that was the case there would be no reason to have a larger turbo at all.

You can get a K04 and run it at 14 psi all day long, and you can get a GT28RS and run it at the identical psi and get a TON more power.

It's not all about psi, it's about volume.

Borg warners statement is true, given that thier speaking in absolute terms, and that there is room for you to move up in pressure without moving into some very poor effiency islands. Given thier K03 @ 10 psi this is very feasable. At this altitude the request boost may be closer to 13 or more to compensate for altitude.

However not every car, (not even every audi) deals in absolute terms, the older cars deal in relative terms, like my 97.

What I want you to quantify if you're not seeing but a negligble amount of pressure is different MAF readings, dyno numbers, and slower track times. That's all hard, real life data to examine, much less explain.