OK, guys. Here's my best shot.
EJ22
'90-96. Non-interferential, definitely.
'97 and 98 are a little fuzzy. Seems that somewhere in the late '97-98 MY there were changes, some of which we haven't seen yet. Late '98, if it looks like a 2.5 SOHC (only 2 timing covers on the front), extremely likely it's interferential. One of these is a 4 month only engine.
'99 EJ22 is definitely interferential. We've done 3 in the last couple of months. 1 year only engine.
EJ25
All are interferential, no matter what year, both DOHC and SOHC.
EJ20
Interferential
It's valves that hit pistons. We have part of one piston that was hit so hard that the only thing remaining intact (sort of) is the head (flat side) and what's left of the ring landings. The head is actually in 3 pieces and is being held together by the rings which are "mostly" still in the grooves. The wrist pin was in the oil pan.
And the failure doesn't have to be as catastrophic as a broken timing belt or failed tensioner. If the belt is off by as much as 3 teeth, it can and most likely will cause valve/piston damage.
If I have ever "preached" maintenance and using Genuine OEM parts, I do it doubly for these engines! Change your oil and never, ever, under any circumstances let them overheat! Use the right octane of gas too. We see burnt exhaust valves in 3 out of 5 engine cores that were replaced for a different problem!
I'm sure Rick (the Master Rebuilder himself) could add to this.
Emily
http://www.ccrengines.com