For all the people here suggesting a grill block it is essential that it doesn't interfere with the intercooler. Otherwise you'll end up dropping your engines efficiency.
This paper is a must read for all people wanting to maximize diesel mileage.
Performance analysis of air-standard Diesel cycle using an alternative irreversible heat transfer approach
http://www.eis.hu.edu.jo/deanshipfiles/pub10311357.pdf
Note I disagree with some of the modeling for figures 4 and 5. It assumes that the cutoff ratio doesn't change. It also doesn't factor in the change in specific heat ratio.