My 400 Srpint boat engine ran at 6400-6500 for between 55 and 60 seconds at a time.
Took some pretty serious bottom end attention to make it live doing that
D-ports by Jim Robertson (cast iron head rule), Roller cam, offset lifters / rockers, 3/8 pushrods and a big Victor and Bolaws annular carb. Sounsded pretty sweet I thought for a little iron headed 400
http://www.youtube.com/watch?v=3ffCw0rR8pI
BTW, boat guys can shift gears when forced to run on land too (I think)
Tom / Jim, care to "score" my shifting in my street 76 TA with a pump gas 455 ??
http://www.youtube.com/watch?v=CVHEZ77gUxQ