[Diesel_Dave]

I know it can be done, although I wish I understood more about it. I've heard that they've done this type of things on F1 car engines, achieving over 110% volumetric efficiency on a naturally aspirated engine.

Unfortunately, vol eff has been a reletively low priority for diesels because they're typically turbo'd and aren't contrained to a fixed AFR. Therefore, you can compensate somewhat (in terms of power output) either by running slightly lower AFR or by running a little higher boost. I think there is definitely a lot of room for vol eff improvement in diesels. After all, increasing vol eff is just like boosting turbo efficiencies. Why it's not done more still puzzles me.

Unfortunately, it's typically pretty hard to do both the design and fabrication DIY.