Thanks for a lot of great info E92fan. Running the N54 well above 400 whp without meth support is a challenge but I guess it may work fine for you with reduced CR and better components. As long as the piston to cylinder wall clearance is sufficient.
I don't know how much meth injection will reduce the combustion temperature but I believe it is significant and more importantly, it is a true octane booster that works and allows for more ignition advance/power. I guess you can find some information about the cooling effect if you search on the Internet or ask the meth system suppliers directly. If you want to study this historically you can start here
http://www.labontemotorsports.com/ontrack/nacawr.pdf and move on from there
