408 l92 l76 issue HELP

[project nightmare]

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l92/l76 m6 car.....somewhat a DD but not really
built for nitrous
408
ported l92
stock l76
11:5:1
all the lower end goodies
1 3/4 headers : ( (for now)
3'' y with no cats, dual cut outs, and borla catback.....
9'' ford with 3:89's...


well i got it tuned this weekend.....it drives really well actually....its a tad harder to take off then before but the exo seems to be the issue there....im really surprised about the drivability of it....i can do 70 on the hwy in 6th with no issue at all....it doesn't have any surging or bucking really.....

Heres the PROBLEM:

it has a bad spot between abpout 2700 2800 to 3100....it flutters and it pops out the exhuast.....It doesn't do it in first , it gets worse from 2nd to sixth....my tuner guy worked on it all day....adding timing helped but we reached a threshold when the knock retard started coming into play.... taking away timing made it worse..... the afr was right on the money.....we went to speed density just to check and see if the MAF was working and it was....i changed the plugs from the really cold ngk to the common tr6's... no change..... we also took either and sprayed around the intake for a leak....NO Leaks.... its smooth before and after that spot....makes no freakin sinse......

Since its likes timing im curious to what some race fuel would do....but.....11:5 seems to be an ok compression for 93 octane....RIGHT?????

Could the overlap on the cam cause this???? it would be worse i would think at a lower RPM with the same load????

If anybody can help i would appreciate any input......

heres the final tune and the a log after changing to tr6 from a step colder...didnt' help a bit
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[Dozer]

Where is the wideband?

[project nightmare]

the log was me driving after it was all said and done....it was widebaned on the dyno.....air fuel is dead on the money...... i also have a fast afr box in the car but its not linked to the log data......

[project nightmare]

ttt,,,,im surprised nobobody has an input



i changed the headers to 1 7/8....still no help.....

[t56rebuilds]

What is up with the map readings in that area? I see them being 97kpa to 99kpa at that area. I would check to see if it is secured in the manifold. I see that with a tps of 55% the log shows 99kpa. That seem kinda odd.