Alex, Tom... Please continue and let me know all about this nitrous and converter control..
I just got involved with one car and that car led to another car. The first car is a 9.5 deck with two kits. The other is a mountain motor with almost twice the engine displacement and three kits. I'm involved because I did one system and that led to another when someone saw the first one. They each have totally different systems.
I have a turbo car with data logging. No nitrous. I have had two converters in my car, one locked stator and one with mechanical diode of the same company and size. The only difference is the stator.
These are my only three comparisons.
Looking at data logs from these three cars (mine with two different converters and turbos), it is pretty evident the nitrous goes through a power gyration if it hits with equal time and ramp for fuel and niitrous. A mixture problem shows on the wideband data if the hit is done down track and the wideband is stable. It does not show on the starting line because the stutter box has the wideband going nuts by pumping air and burned mixture randomly across the sensor.
One car also had backfire issues unless we ramped the fuel in ahead of the nitrous. Doing that also smoothed out the short falloff in acceleration and RPM as the system stabilized at proper mixture.
With both F and N solenoids near the injection points, and with a fuel bypass regulator circulating fuel to keep cool fuel waiting at the solenoid, opening both at the same instant always results in nitrous leading fuel enough to cause a very brief power falloff problem.
My turbo car has none of that. It does show the same expected false wideband readings when stuttering or within maybe .1 seconds after transbrake release, but it does not have any of the sag after launch. I have a smooth upward curve no matter which converter or turbo I run. I intentionally turn closed loop off and run strictly on a fuel table to make sure the system is not trying to correct fuel using the stutter-confused wideband mixture data. If I let the mixture correct, then I get a similar or worse falloff just like the nitrous cars have. I suppose I might think it looked like a converter or tire issue, but looking at mixture I concluded it was mixture and that turned out to be true. It goes away if I force open loop and run off a table until I am past where the wideband is nuts.
So we have a few things pointing to mixture. My turbo will do that sag if I let the system adjust mixture off the wideband when the wideband is still nuts from the stuttering. Both nitrous cars do it. One for sure is fixed by ramping in the fuel ahead of the nitrous. The other car is in the beginning stages, but had the same problem.
This is probably all I can offer.