Quote:
Originally Posted by moto-mike
I'm puzzled why you're seeing that. We have never observed this in our testing on the road and on the dyno nor track logs from customers. Once combustion stops the motor can't spin any faster regardless of what the rotrex unit wants to do. May be how your tune is implementing the rev limit vs what we do? Data acquisition issues?
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Incorrect. This behavior has nothing to do with the Rotrex, although the Rotrex does amplify it a bit, as with ANY forced induction solution.
Once combustion stops, the motor's RPM's rate of acceleration goes from positive (torque output) to negative (engine braking from compression and friction). It doesn't mean the engine's RPMs instantly stop dropping. The momentum of the rising RPM will carry it upward, and the decrease in inertia from disengaging the clutch allows for that momentum to act upon engine RPMs even faster. Combine that with the tiny DBW delay, and a 400-600 RPM increase with a throttle lift and clutch in isn't unheard of at all.
An analogy to this would be throwing a ball up into the air. The ball's trajectory is analogous to engine RPM. The moment the ball leaves your hand, the acceleration force (combustion) disappears. There is no longer an acceleration force upward acting on the ball. However, gravity (compression and friction) is always acting on the ball, causing the ball's trajectory to become a parabola. Even through the acceleration force isn't acting on the ball, the ball's momentum carries it higher (the RPM spike), before it eventually stops dropping.
Velocity is the derivative of acceleration. Acceleration's force is not instantaneous.
I've observed this type of behavior on EVERY type of tune for this car. It's partially physics, and partially the relationship between TPS and PPS. You cannot eliminate either one, unless you've developed an ultra low friction, low inertia engine, and have completely upgraded the ECU hardware with a far faster unit.
I can post datalogs from @
DeliciousTuning, @
ptuning, JamesM, and, also you, that exhibit the same behavior.