Actually we did see the ECU being very active in all of our Dyno pulls. We did a minimum of three pulls per baseline and/or modification and the main thing I saw that was radically different between some of the pulls was the air fuel ratio. While we did not monitor actual throttle angle on all of the pulls, I doubt that the drop in power that you may have seen was due to the throttle shutting as much as it was due to the ECU editing fuel and/or timing.
What we specifically saw on stock was the first pull was really jagged (smoothing shut off in all reviews of the files), stock ECU runs really lean (~14:1) until about 4500RPM and then drops markedly to ~10:1. Subsequent runs go rich sooner, dropping into the high 11's in the ~2500RPM range. This smooths the midrange power numbers and they go up and are less choppy. The numbers on the three stock baseline pulls (2.5L, 6speed) are 161.46, 163.90, 164.23. That is the peak power.
Comparing this behavior directly to the same car with Short Ram Intake and Dual 60mm exhaust system, the three pulls do indeed go down in power from the first to last - but the overall amount of decrease is less than 1hp. In addition to this, the radical fluctuation of the air fuel ratio during wide open throttle (WOT) runs is not remotely as reactionary as it was during the first three baseline pulls. The best of these pulls (second when looking at torque and hp) is 171/171.
I think what we may be seeing while dyno testing these cars is that the ECU is having to adapt to a WOT at load condition that it has not experienced in the past and we're just seeing the learning - sometimes it shoots one direction (rich vs. lean) and has to lean out to hit its assumed target, other times it shoots the other direction (lean instead of rich) and has to richen the mixture to hit the target. The results are not always negative relative to power building. Best to Worst, Worst to Best and Best to Best, the modified cars built more power. Days later on the butt dyno, the car was just as good if not better than it was when we had rolled it off the dyno after we did the pulls testing the intake and exhaust in tandem.
That being said, I do not have any doubt that having some access to tune the parameters set in the ECU would improve greatly the potential to build power in these cars with the aforementioned modifications. I know that with the MS3's, they need to be run for an extended period of time after a new induction system has been added prior to tuning the ECU so they may calibrate the MAF, then tuning can be done. I think we may very well be seeing similar behavior in our test results (and yours).
Jason Griffith
Product Development Engineer
Corksport Mazda Performance