I've been doing some tune work on a manual 6-speed 2013 Corvette Grand Sport with BTR blower cam, headers, ~90 lb/hr FIC injectors, and Procharger P1SC. This car is making good power until a point between 5,300 to 5,800 rpm where there is a step drop in power, airflow, injector pulse width, and injector duty cycle. Roughly a 100 rwhp drop that maintains through the rest of the pull. This power drop has been consistent on 5 or 6 dyno pulls.
From my data log I do not see any change in throttle pedal position or voltage, ignition timing stays 17? advance, none of the torque management pids show any sign of activity, and AFR is steady between 11.7 to 12.0. I can correlate the drop in power on the dyno graph with a drop in MAF, MAP (unfortunately this car still has the stock 1bar MAP but reads up to 120 KPa) injector duty cycle, injector pulse width, and can see RPM curve flatten out.
Observations during testing:
- Car has a twin disk clutch and there does not appear to be any sign of clutch slip (no RPM spike)
- No sign of throttle blade position change during the pull
- Blow-off valve appears to close and stay closed during the pull
- No obvious sign of belt slip like dust or excess belt heat
- Boost gauge rises to a peak of 5 or 6 psig then drops when power drops
- I do not know what spark plugs are used or what the gap is
- I do not know if the crank pulley was pinned - need to verify that
Anybody want to take a crack at trouble shooting this power drop? I feel like it is definitely airflow related, and then fuel flow (injector pulse and duty cycle) drop as a result of less airflow. But what is the root cause?
Clyde