I want to know, if anybody knows, what can you tune on a naturally aspirated diesel. No turbocharger, no supercharger, no procharger. Just NA. And also why you can't have water/methanol injection on indirect injection diesel?

How expensive would it be to fill the precombustion chamber and drill out a hole for direct injection? What else is different between IDI and DID?
I just feel like learning more about diesels right now.