Well, sounds like there are a few things to comment on here. First is the "groove" concept, of cutting one or more grooves in the squish area of the head. The other is the "nitrogen" question, which confusingly is what is referenced on the main page. The site certainly has the tinfoil-hat look and feel, with lots of strange incomplete thoughts and undocumented assertions. However, digging a bit through the chaff does seem to have some interesting tidbits of actual, real data. The gains are small, but certainly seem realistic. There is no good diesel data, however, so this might be misleading to those of us working with the heavier fuels... I would say that it seems like the modifications seem to have some adherents, and if you have an inexpensive 6/1 head or whatever laying around in which cutting a groove sounds like an OK thing to do, then I'd be interested in hearing what the results are. I don't know what the downside would be - I'm not smart enough to do the math to see what kind of compression changes would happen from removing a cubic centimeter or so of metal out of the inside of the head. My gut says "not a big deal, so give it a shot" but someone who is better at those calculations should take a swing at it. Certainly, the Lister(oid) community has a much better chance of empirically proving any of these "fringe" energy efficiency theories - our engines stay at exactly one RPM setting once started, and they produce an extremely predictable amount of power in a stationary setting, and are very easily monitored for various temperatures, outputs, and inputs requirements. Should be a quick determination as to what works and what doesn't, no?