1220hp E40 5400rpm 130hp power loss! Pleas help

[nvr2fst]

Hi Everyone,
I have this nagging dip in power with my TT corvette. The car makes great power, runs great (minus feeling the dip at WOT) I've tried a million different things to fix the problem but I simply can't find where the problem lives.
First I'll explain what I've tried:
timing adjustment (higher and lower) in this spot. No change
fuel adjustments (leaner and richer) current AFR 11.65. No change
I tune the car myself but I've had 3 other tuners look at the logs and current tune and we can't find an error.
Different intakes. No change
Different exhaust manifolds. No change
Measured back pressure (pre and post turbos) all within reason.
Information:
It looses 100whp and 130ft lbs of tq
It is always at the same RPM.
It did it with my old 408 and different cam/heads
Currently still does it with my 426lsx
Boost is solid (no dips or spikes)
Zero spark knock
AFR is solid
The dip only noticeable above 1000hp.
I'm running the stock E40 ECU. I think I'm one of the few and maybe the highest with this 1 off GM computer. Maybe it's a problem but we can't find it?
Any thoughts?

1200hp dip.jpg

[mowton]

Don't see anything glaring......Dyno issue?

Ed M

[nvr2fst]

Don't see anything glaring......Dyno issue?

Ed M

I don't think so. You can hear it and see it in the log in the cell counts. I also use virtual dyno on the street and it shows the same problem in the same spot.

[10_SS]

stick an old fashioned timing light on there during the run... also hose clamp up a thermocouple to the header

[ecotec88fiero]

stick an old fashioned timing light on there during the run... also hose clamp up a thermocouple to the header

I would really want to see actual timing like 10_SS said. Where is the wide band located? I would want to see what each bank was doing at the time of the power loss too.

[GHuggins]

Is it dropping a cylinder or at least feel or sound like it is? Only things I can see in the data log is that the issue happens at peak boost where it looks like it's making right around 22psi. What happens if you pull back boost a little? I assume your using a boost controller? At this same time your fueling leans out .3 from commanded = shouldn't be anything to worry about, but it does go from rich (11.2) to leaner (11.9) when the problem occurs? Again, wouldn't think it to be anything to worry about... Obviously engines are different. Were any mechanical parts reused between the two besides the turbo setup such as ignition components?

Other than this and since it happens at the same rpm every time and peak boost happens here, wondering if it's hitting some sort of built in limit withen the ecm?

[schpenxel]

It's getting close to the MAP limit but I don't see it ever hitting 255kpa

Would be interesting to reduce boost a few psi just to see what happens