318 Compression ratio

Here's an article by mopar muscle magazine, 318 built for 400 hp. Interestingly enough, they used magnum heads. Anyway, its a pretty thorough write up, although I think that them ending up with EXACTLY 400 hp is a little suspicious. But after all its a magazine article. At any rate, they did follow all the rules for building a solid 318, ie, zero deck pistons, closed chambers, increased compression and better flowing heads.

Their combo-
KB 167 hypereutectic pistons at 0 deck ( block was line bored and square decked)
Magnum heads (59cc chamber) stock out of the box
10:1 CR with a .040" head gasket
Comp 280H cam
TTI headers
Factory windage tray

Now, whether or not that will actually get you EXACTLY 400 hp I don't know for sure ( I think it'll be a little short without the dyno tricks), but it should put you in the ballpark. Unless you go use their dyno. They did change over to synthetic oil and slapped on a 1" spacer to get there. Also, that was at 6,200 RPM.

http://www.moparmusclemagazine.com/techarticles/mopp_0409_318_engine_build/index.html