After long, hard uphill pull, testing on hot day. Usually around town it's half of that even when flogged hard.
Aluminum doesn't melt until past 1100 F, but the physical properties for most alloys start declining quickly between 450 & 500 F. Some alloys are formulated specifically for strength at higher temperatures. NASA has been on the case though and actually developed some of these specialalloys fairly recently(published 2003):
Quote:
Originally developed by NASA as high performance piston alloys to meet U.S. automotive
legislation requiring low exhaust emission, the novel NASA alloys now offer dramatic increase
in tensile strength for many other applications at elevated temperatures from 450°F (232°C) to
about 750°F (400°C).
Much more here from NASA's own website
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030106070.pdf - Malossi, Polini and all Vespa piston vendors, please take note!