You are trying to evade your initial statement:
Originally Posted by swamp2
direct injection will largely mitigate turbo lag, when the two are carefully integrated and matched by BMW M.
There is not mention of VGT in that statement which ends at period. I will therefore repeat my answer to you: this is a misconception direct injection can not "largely" counter turbo lag. If you do not stand by what you initialy write or recognize your misconception I will just have to quote my first answer to you again.
As I said in my post only Variable turbine geometry can "largely" eliminate turbo lag in a gasoline engine. Again, please don't take my words to make them yours: you do Not mention VGT or VVT in your first post, only DCT. I have to hold you down to your words. If you persist I will quote.
BTW fast downshifting with DCT only avoids loosing boost pressure by keeping revs high which is not really a solution to the turbo lag problem at all rpms.
Thanks for giving your source on the claim of 2-3x the rpm for the turbo with DI engine. Prof Arcoumanis is certainly an authoritative figure in the field of internal combustion engines. Since I do not have his book I would ask that you elaborate on this. I suspect that this kind of result is based on a less aggressive version of late ignition or ALS anti lag system which in its original version applied to rally race cars was a blatant violation of any emission standards. The ignition being severely delayed, the exhaust valve is starting to open before the end of the power stroke. Luckily the turbo sits right there and the end of the explosion keeps it turning. The effect is vastly lower response times even at engine idle speeds. The only way this could happen in a commercial car is to reduce the nitrogen oxide (NOx) emissions by using exhaust gas recirculation (EGR). Replacing part of the intake air by inert exhaust gases which have lower oxygen density. Where the DI becomes handy is by it being able to inject fuel in the latter stages of the compression combined with ALS. But this would be a pretty big one to pull off more of a university professor theorical research paper than actual practical engineering work. Therefore I stand by what I said the next M might be either twincharged DI diesel engine or variable Turbine geometry (VTG/VVT) turbo gasoline engine. We will just have to wait and see.