[Nezil]

Thanks so much for taking a look at this SeanWRT.

Originally Posted by SeanWRT

From the log, the shift takes 1.4s to complete, from pedal lift to it 100% back on. And in it, there's 1 full sec with 50% or lower pedal angle.

Agreed.

What does ECU do on pedal lift?
1) Throttle closure, which pretty much follows pedal input, as a direct and most effective manifold boost (MAP) control measure.

2) The throttle closure makes the backpressure to the compressor (the cold end of turbo). That's when DV comes in (log doesnt show unfortunately) and release the charge pressure (the boost in the charge pipe, or Pre Boost). To avoid mechanical failure. See there is a short time in the log (shown below) when MAP is cut but Pre boost is significantly higher until they're closer? That's what it is.

3) Wastegate fully open (to 0%) to release the pressure on the impeller.

I'm with you up to here.

When DV's done with boost control, WG reacts to boost target (or torque target which ultimately is pedal input) with correct opening %. As said earlier, WG is a lagging measure for boost, and only a reflection of turbo shaft speed compared to boost target.

I'm not quite sure what you mean here, but if we add WGDC to the chart you posted, you can clearly see that it doesn't close to 100% until a full second after Accelerator Pedal Position, Torque Target and Throttle Angle are all at 100%... My question is very simple... Why is the Wastegate not closing to 100% for this 1 second period. As soon as it does close, the turbo spools up far more rapidly.

A simple put - Lag is from too much off pedal time.

In this particular case, when you go back to 100% pedal, the boost is already 11.8psi off (MAP=Preboost=3.4psi, rel="ugc" target=15.2psi). See the big boost delta area. It takes a whole lot of time (another 1.3 secs) for boost buildup to target.

But my point is that boost would build up much quicker than 1.3 seconds if only the waste gate would close. You can see the change in boost pressure rise happens suddenly once the waste gate closes, but it's a full second after you're back on the gas after a shift... And you can feel this when driving very easily.

Revisit my conclusion - human shift is too slow, ECU has no choice but dump boost for mechanical safety. And boost takes time to recover. Hence the lag. I guess stick shift fun comes at cost LOL

Hope it makes sense.

Sean

I guess what I'm saying is that I expect some lag from a human shift being slow; it's inevitable, just as you say.

Throttle closes, DV dumps pressure and the waste gate opens all as soon as you let off the gas. Boost pressure drops dramatically and once you're back on the gas the pressure is way off target. You explained it well and it all makes sense.

What doesn't make sense to me is what happens once you're back on the gas - isn't the waste gate delayed closing behaviour making the situation far far worse (1 second more lag) than it needs to be?