Mad Dart Wrote:The second map is better, more efficient in the 79% efficiency range. With room to increase the pressure and airflow and still be in the sweet spot of that map.
In my case, using the 318 of the OP, the first one is a better choice. Why? because of the different pressure ratio created by higher altitude, that i live at.
Even thought the turbo is often called a altitude compensater it still will affect your choice on a turbo.
If you input 11.8 (average air pressure were i live) in place of the standard 14.696. you will see that it changes the maps. Causes the GT4508R to be running close to the 72% line and never make it into the sweet spot. Were as the GT4292R comes up the 78% line and then runs straight across the sweet spot or best afficany(sp) line.