this has been discussed extensively before... There is basically 2 camps--one says Stillen cools better than Greddy, one that says Greddy flows better than stillen. Do a search on "intercooler" or "morepower2". Morepower2 is Mike Kojima from SCC. He posted some dyno info awhile back on HKS vs stillen and has some discussions about greddy vs stillen. Also check out this thread. Some info there as well.