So I'm working on a brakeboost feature here
Aim to make a steady state speed when brake slightly pressed with wot to build some boost via neg ignition

Basically logic here
When b_br true and wiped > 95%
Nmot_w has nailed
And in next cycle nmot_w compared with thus specified nmot
Some map here with nmot difference vs ignition offset and finally this offset applying to let's say zwgru

Yay or nay?

Well i was interesting in ignition cut only
And tonight has some time for that

Made some routine with flags, caps etc, called right before zwgru safety caps calculation
Spent some time to own safety caps, two paths for a negative and positive acceleratin, dynamically ign offset etc

Aand funny result here, my oldie TD04HL-19T which normally pushes 0.7 @3000 and 1.8 @4500 with ~25 ign starts goin crasy with just -7 ign
Pulls 2.0 bar (map limit) @3500 and continued acceleration with 0% wgdc

Thats a really nice result but too hard to control the boost. In fact i was thinking that the problem could be with an underboost but not the over-

It seems youre right about spark cut. i dont wanna those bangs but seems there is no way without

So the questions:
How ign angle affects on a boost? What is the optimal for rolling launch? Lets say +20 is a good power but not for boost, -7 awesome boost but not for power and produces high EGT. What about -15..-30? Maybe i should go further, or thats a stupid idea? Could this few secs pushings with neg ign harm the engine with EGT?

Less advance = more boost, obviously.
If you are making boost even with 0% WGDC, then it means your WG is not big enough.

If you want it not for the loud sound then better approach is to blend out some cylinders as you start hitting the target RPM...
That will make less boost and won't spit fire from exhaust.