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A few thoughts.
Your car is a factory msport right? In that case top speed is limited to 155 stock. If you unlocked the limiter and hit 160 that's more than 155. Maybe that's all the engine can put out? It is just a 4 cylinder so I'm not sure getting much faster should be expected. Am I wrong? Also the speedometer only goes to 160 so how were you able to determine if it were going faster? Just wondering.
Second, did you do a before dyno to compare the delta? (Same day)
And last, I have GSR stage 1. I know what you're talking about with the stutter at WOT. Now I've been curious about this. Correct me if I'm wrong but I thought when stock you can go WOT in any gear even at lower RPMS. The car just picks up acceleration when possible with no stuttering. Which I've always thought was a bad idea with forced injection due to excess strain so it wasn't common practice for me. None the less this observation never showed an indication anything was wrong. Now after getting the tune your described stutter presented itself. My theory is with the extra boost and perhaps some other ECU settings altered, the engine is told to not hold back and pick up and go (perhaps stock has more safeguards?). But mechanically there is an extra strain on the drive train, hence the stutter. Again these are just my thoughts..
I'm not sure if I'm correct or what the real issue is, but I have altered my driving style. I only go WOT in 1st and 2nd (no stuttering at any RPM), unless I'm way up in the RPM band for the higher gears. In doing so everything is dandy and no stuttering. And that also jives with the conventional driving style with forced induction.
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