[SeanWRT]

Originally Posted by Nezil

Here's the link to the log SeanWRT: http://www.bootmod3.net/log?id=5e684a57d10b43215e7f315b. Ignore the stuff at the start, it's only the part at the end that's relevant of course.

Thanks for sharing.

It's clear and my intepretation is no issue from BMW tuning. No delay whatsoever in reacting.

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.

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. 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.

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="" 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.

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