this is an older article, however i thought it was pretty interesting given other conversations on the board.
it really is a very good technical read.
http://forums.clubrsx.com/showthread.php?t=323710
in short a company had made a cam for the k20a, which is the engine in the newer civic type r, integra type r and rsx-s, etc.
stock this motor puts 171 hp and 125 ftlbs. to the wheels. so they designed cams for this motor with your regular bolt ons (intake, header, exhaust, chip). the cams and boltons threw out 248wheel horse power and 172 wheel torque. imagine what its rating is at the crank, or even at the brakes!! not bad for a 2.0 liter
keep in mind this motor is still just as reliable as it would be from factory. upon testing the motor they had reliazed that there was a lot more potential in the motor so they designed a much more agressive cam to take full advantage of the heads abilities. they hit a bottle neck. the bottom end wasnt to fond of revving over 8500 and the newer cam would make much more power up there.
in short they built a race motor by overhauling the bottom end. extending the stroke 2mm just for more displacement for the cam. then they also increased the rod length to maintain a similar rod stroke ratio while also using lower profile pistons to work with the longer rods and stroke and maintain a higher compression ratio. forged internals, of course, were added to deal with all the new stress and to lighten things up.
they also did some head work, but they had not ported the head because it had perfect flow already. so headwork in this case is the cams, valvesprings, and retainers. factory head core, factory rocker assembly, factory valves.
now a 2.2liter race motor, it pumps out 312 all motor horse power and 220 ftlbs to the wheels. in a car like mine this is more than capable of 11second passes with some sticky tires and probably an amateur(myself) driving. a pro could no doubt get it into the 10s granted this motor now racked up a total expense of over $10,000.