This is really simple.......
All Pressure is....Is a Measurement of resistance!!!!!!!!!!!Here is what you need to look at......
The basic fact remains that you have to have restriction to make pressure!!!!!!
It is also possible to have better then 100VE in competition engines ....
Nascar is slightly over 100% And Formula 1 is way over 100%!!!!
Increasing the flow rate of a engine causes it to move air more freely!
When you more as much air as we are with Seb's engine we are off the charts on either of those GT28RS Maps.
If you do the math you will realize we are moving 42 LBS per minute of air and that is simply way more then the compressor map shows or was designed for!!!!!! This is why you can not get the turbo to spin harder to make more pressure because your simply beyond the choke point of this little turbo with the crazy power it is making and IMO happily at a lower boost then imaginable.....
It is intirely possible with a more restrictive engine that these turbos can easily hit 28 PSI.
Obviously if you have stock manifolds and stock cams and valves on a Z engine it will make more boost (And less Power)
Again I make 25 PSI with mine with larger valves , But stock Cams.
Here is the math to the air flow Seb's engine is moving to reach the power level it is at...... The formula off Garrett's site: 
Where:
· Wa = Airflowactual (lb/min)
· HP = Horsepower Target (flywheel)
· = Air/Fuel Ratio
· = Brake Specific Fuel Consumption ( ) ÷ 60 (to convert from hours to minutes)
So if Seb's car makes 669 RWHP we can say he probably has a 15% driveline loss, so that makes it close to 769 flywheel hp. 769*12*.55/60=84lb/min divide this figure by 2 since we are splitting the motor and using 2 turbos. We get 42lb/min.
As you can see we are way off the turbo Map!!!!
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