Non Interference Engine?

Hello, I read from somewhere that non-interference engines are designed so that pistons and valves do not collide in case of timing belt/chain failure. Is N54 a non interference design? Just curious...

I have not seen a modern BMW engine that is non-interference. Since compression has to be so high nowadays, chances are you will not see many non-interference engines from any manufacturer.
However, with a Valvetronic engine if the chain failed when the Valvetronic cam was at lowest lift, it is possible that the pistons would not hit. That still does not qualify as non-interference.

I see... Thank you for the explanation. But should the compression be so high for direct injection, normally aspirated engine too?

A DI engine usually can take advantage of a higher compression and a leaner mixture due to fuel stratification and the cooling effect of the fuel being vaporized when it is injected, so basically they usually have higher compression than a port injected NA motor.

Thanks again. I was able to sort of understand the benefit of stratified charge and odd shape piston crown, etc. only after reading through Wiki. It's still too technical for me to grasp fully, but I am beginning to fully appreciate the high tech engine in my 335i. Especially with my right foot down.