Originally Posted by Angel

I get the impression that you give up a few things in a non-interference engine. First off would be a 4v/cyl valvetrain - to stuff all those valves in you must put them at an angle, and then open them as far as you can (to optimize breathing) and unless you give up a stack of compression ratio (ie- make the combustion chamber really big or the stroke really small) the valves will hit the piston when fully open at TDC. I'd be curious if any of these non-interference motors are 4v per cylinder.
I mentioned valve lift - no matter how many valves you have, or what your bore x stroke is, the farther you open your valves (to a point) the better the engine breathes, which means more power, better fuel economy, or some combination of both. Engine makers are always looking for these and probably have no problem opening a valve so far that an otherwise non-interference motor becomes an interference motor when you 'tune' it so far.

-John