I read somewhere that they are aluminum (for improved cooling they say)
but cast iron cylinder sleeves. I'm ok with that. Also, the manual
for the c7550 says this:

This air compressor pump is capable
of running continuously. However, to
prolong the life of your air
compressor, it is recommended that a
50%-75% average duty cycle be
maintained; that is, the air compressor
pump should not run more than 30-45
minutes in any given hour.

That's probably ok for me. I'd want continuous duty for spraying from
time to time, but would never do that every day. And I'm sure I would
empty the gun and need to refill before the 30 minutes is up. I can't
imagine standing in one spot with an air sander for more than 30
minutes also.

I'd probably rather have the IR also. But I'm trying to strike a
balance between cost and performance. This is probably already much
more compressor than I need. My main uses are going to be hvlp and
automotive work. I might get into metalwork and stone sculpting some
time in the future. I'm also trying to take advantage of the $150 off
sale at amazon.

brian