L4189, thats very interesting. What is the mechanism to reduce NOx by reducing the temperature gradient? I would have thought that promoting higher temps to be kept within the chamber by reducing the gradient between charge and chamber wall would have had the opposite effect - needing less advance and creating higher peak temps?
TDImeister, being already optimised was an assumption, but if we dont assume some constants at least, the OP question is to broad to answer. I only have experience of HSDI engines, from 1000-2500rpm steady state these tradeoff ratios are correct for a good range of engine displacements.