Not a popular or often-discussed upgrade on DSMs, it nevertheless seems to show up regularly in highly modified engines. It also seems to be catching on more with non-turbo owners interested in performance mods, perhaps partly because of their middling price point. Scot Gray has reported good results using cams from the now-defunct Mutiny Racerwerx shop, and many of the faster cars include cams in their modifications list.
On the flip side, those who have installed new cams have often reported negative side effects, such as low vacuum and poor idle, which appear to be endemic to cam changes. Much more rare are first-hand reports of verified performance gains, making DSM cams a doubtful upgrade when compared to other modifications. (Owners of highly modified engines often change several things at once, making the effect of any single component unverifiable.)
To add to the confusion, Leon Reitman actually removed upgrade cams from his car after finding they provided no performance gain, despite HKS' claim of 11hp. David Buschur stated here that cams would not be a worthwhile upgrade for 99% of drivers, as the cam change only makes more power in the higher RPM ranges. It has also been reported by Kyle Zingg in the Dec. 21, 1998 Digest that a prominent vendor recommends against changing the cams, as the stock cams provide the most power.
The bottom line is that most owners do a great deal of work on their DSMs before thinking about cams. Turbo, intercooler and other such advanced upgrades are known to provide significant gains, so owners are recommended to pursue them first.
The Last Word: The more modern cams for DSMs can be great - as long as you have enough air running through the rest of the system to make them worthwhile. Most people opt to 264/264s, but 272s are - theoretically - also available They can be hard to get a hold of,