you answered your own question...it's about compression and that's it. Lower compression engines can be non-interference engines but they won't develop the horsepower that interference engines are able to in a smaller (and hence more effecient) arena. So if you want the same performance from a non inter engine you would have to make the engine larger thus negating any performance gained. Both in weight/fuel economy and the associated handling loss of such added bulk. I haven't heard of any decent non-interference engine on a performance engine since the hemis of the late 60's or early 70's muscle cars (and you know where they are now)..And don't even get me going on diesels.....it's simply an enginering fact....hell, do they still even make a non interference engine that can be sold in the US...I would think that the EPA would have strangled by now......