Nick:
Thanks for clarifying that for me. It has been > than 20 years since I studied piston engines. One of my aviation regrets is that I never got to operate a BIG Round engine like the Wright 3350 Turbo Compound with Water/Meth or one of the BIG Pratts. My biggest piston is a Turbo Charged Continental 520.
I do now it is all about temperature in the Allison 250 Engines though. Flying the Straight L with water /meth was fun and it made a significant difference in performance. I often thought that it would have been a neat mod on the S76A.
http://www.pilotfriend.com/aircraft%...evelopment.htm