The continued existence of interference engines baffles me. Is there something they do that much better than non-interference engines that continuing to produce them is worth the risk of trashing the engine if the belt breaks? Seems to me like that kind of Achilles heel just can't be worth whatever benefit the design has.
Smaller combustion chamber helps with the compression ratio, especially on cylinders that are already low displacement. Gets you more power per CI, usually better economy, depending on some other things it can let the computer play with ignition timing a little more as well. It also tends to be needed if you're running variable cam lifts and/or Cam timing. It's more difficult to stay non interference as you widen valve lift profiles. Again, especially with smaller displacement engines.
It's also not like it actually frags the whole engine when it goes. *Usually* it just bends a valve or two. If it breaks one off, then you might need a head and piston, and maybe some machine work. So from an engine design standpoint, you get a more powerful AND efficient engine with more freedom to play with other features, and you add a timing belt change to the scheduled maintenance around 100k. No real downside.
From an owner's standpoint, well there's a lot of scheduled maintenance that if you blow off and ignore you can do serious damage to your engine.
