I know 2 people personally with over 500hp on stock K series internals. One is a K24a4 making 518hp (http://www.k20a.org/forum/showthread.php?t=63867) and the other is a stock K20a2 making 618hp (http://www.k20a.org/forum/showthread.php?t=82101&highlight=6262). Both are up here at ~5500' elevation on E85. There are a few other people on here that are making 500+hp on stock internals as well, so 350hp really isnt much to worry about. Get a good tune and good fuel and you should be good to go.