To be honest with you I have no experience with how diesels behave with W/I. Since a diesel is always over supplied with air and the throttle occurs on the fuel side, I'm not sure how much effect intake charge air cooling will make a difference, or how much water they can accept. My impression is that the tractor pull folks use it mostly to hold down EGT's.
This paper implies that the presence of water may delay the ignition event slightly, although this is an experimental direct injection model of the combustion process, it may be useful.
http://www.cae.wisc.edu/~rutland/res...00-01-2938.pdf
http://www.wartsila.com/english/pdf/..._water_inj.pdf
This page also comments on direct injection for emissions control and suggests a water / fuel ratio of .4 - .7
This web page has a guy who says he pits for a tractor pull and will explain how to set up a water injection system. It might be useful to touch base with him and pull him into this forum for everyones edification.
http://www.turbodieselregister.com/f...threadid=77726
I'll keep looking around and see what else I can find.
Larry