Here is an old BMW M30 with a BMW Turbo doing the unreal.
It even idles just fine. http://www.viinikellari.com/745/performance.htm
He is the m102 guru who built Tuoma Perfection Turbo Upgrade.
On an engine with 500.000 km +
Fuel: 98 octane unleaded (with lead substitutes)
Ambient temperature: 8 degrees celcius
Turbo boost: 1.1 bar (16 PSI)
Gear: 3rd (40 km/h at 1000 RPM)
RPM range used: From 1600 to 5250 rpm (210 km/h)
The known limitation is the exhaust system. The standard exhaust can not handle all that power so some of it was lost in the pipe due to resistance and back boost. How much was it we don't know exactly, but a good guess is some 40-50 hp (a bit over 10% of total power). We assume that with proper exhaust system these tests might have given some 450 hp at 1.1 bar. New exhaust has already been designed and we know that it can handle min. 500 hp.
We run the engine also at 1.5 bar boost and everything worked well for a very short time we tried it. The turbo, wastegate and chip were able to handle that, but the the fuel system could not.
At ALL power levers we recommend to use
1) A 3 or 4 wire o2 sensor and a mixture monitor such as the HALMETER AFR30 ( http://www.halmeter.com/
2) Cartech Rising Rate Fuel Pressure Regulator ( http://www.cartech.net/
Interesting point is also that the best power and torque are at fairly low rpms. That gives the opportunity to move those up by changing the camshaft to steeper version. That would further increase the max power quite a bit. Torque would go down in low revs, but that does not matter as it is unbelievable high anyway (you will see it in the curves).
Assuming that the 50 hp/0.2 bar ratio is correct all the way from 0.9 bar to 1.5 bar we can estimate the maximum available power from 745 3.4 l engine as follows:
1. Standard engine/exhaust/fuel supply with Motronic chip upgrade and boost control modification
400 hp at 1.1 bar (maximum constant power)
2. Standard engine/fuel supply with chip/wastegate mod and 2.5"exhaust system
450 hp at 1.1 bar with Cartech Rising Rate Fuel Pressure Regulator. (Extra fuel injectors or may be needed for this power)
3. Standard engine with chip/wastegate mod + 2.5" exhaust system + Cartech Rising Rate Fuel Pressure Regulator + add-on fuel injectors
550 hp at 1.5 bar
4. As no3 but with steeper camshaft
600 hp at 1.5 bar
This is 16 psi or 1.1 bar