[Dimman]

Originally Posted by serialk11r

It's not about the peak torque, it's that combustion stability is affected across the board so you'll probably have rough idle and misfires or significant torque fluctuations, all that shit, if I understand correctly.

arghx7 indicated that the ports on D4-S engines are likely a compromise between tumble and flow, because you really do need the tumble at low speed for the direct injection to work. The port injectors give you more room in terms of how much tumble you need.

Basically, you're kinda forced to have a flow compromise of some sort, and I have this gut feeling that TGVs are the better option. Now of course BMW and Porsche and whatever don't seem to have issues with this, but arghx7 makes it sound like their stuff is much fancier and more capable, so I'll believe that for now even though I don't quite understand how it works. For Porsche I think reduced valve lift increases tumble flow or something, so they're okay. Not sure how BMW deals with high/low rpm compromise on their S-- engines with only double VANOS, but I'd guess their injector placement and firing have something to do with it.

Read the paper. The whole point of the D4-S was to break the two compromises. 20% VE penalty over 6400 rpm has no business in a performance motor.