here's my theory of it. clearly all remained equal. There is one weakness in HPT up to the current release and its the wastegate PID. Aint none. I mentioned in another post that the engine ecu also has predictive responses for self protection. I qualify this that I am just a novice but, pretty astute and I won't put my self out there w/o at least some logic that seems to hold water.
https://en.wikipedia.org/wiki/Boost_controller
"The basic algorithm sometimes involves the EMS (engine management system) "learning" how quickly the turbocharger can spool and how quickly the boost pressure increases..." blah blah....
"Stepper motors allow fine control of airflow based on position and speed of the motor, but may have low total airflow capability. Some systems use a solenoid in conjunction with a stepper motor, with the stepper motor allowing fine control and the solenoid coarse control." etc...etc...
"Since less positive pressure can be present at the wastegate actuator as desired boost is approached the wastegate remains closer to a completely closed state. This keeps exhaust gas routed through the turbine and increases energy transferred to the wheels of the turbocharger." Ok OK OK...
TADA!-
"As overboost reaches the programmable maximum, the EMS begins to decrease the bleed rate through the control solenoid to raise boost pressure as seen at the wastegate actuator diaphragm so the wastegate opens enough to limit boost to the maximum configured level of over-boost."
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I believe the ECU also measures (or Calculates) spool rate. if it clocked over the limit in the ecu, then the ecu was keeping the wastegate open. I see this with the lower cylinder air mass in the logs. Overboost (spool rate) was triggering the wastegate since the turbine was faster than allowed with the free flowing exhaust. Also I could tell just by listening that there was no really good turbo "sound".
Now with just a little extra back pressure it came back to normal power, good spool, whine, power, BOL woosh.
By ONLY adding a straight pipe muffler before the Y pipe, in the tunnel.
Refute, Rebut and Reject as you will. But I was There!
I guess the only logical thing to do is jail break overboost protection, but this marks my stopping point.
Also keep in mind this was with a tuned ECU that is already demanding torque and thus boost at higher levels. So untuned ECUs probably still have a higher margin for overboost and so they would/may not see this issue. Unless some one tried straight pipes. ?
Anyways that's my essay.
W./