@mazda3sport: I own a '10 MZ3 s Sport with its 2.5l L5-VE engine
. The engine has a longer stroke than the 2.3l variant used in the mazdaspeed3, a forged crank, and the block is cast of a steel-molybdenum alloy with higher heat tolerance than the steel used in the L3 series of 2.3l engines. Because of the longer stroke, the redline maximum for the 2.5l L5-VE is lower, 6200 or so. Still, it's been (being?) done, the "MAZDA3 turbo sedan" at the 2010 SEMA show Mazda showcase
No clue how long it stands up to boosted duty, but they were achieving over 250bhp at 10 p.s.i. boost according to that article. I get the impression that you can do it, but it's expensive and probably problematic to boost much more than that 10 p.s.i. without at least shortening the stroke.
I'm mostly curious how their setup works, where the turbo can provide useful boost... The NA engine has a lot of useful low-RPM power, easily down to 1500 RPM in many instances, I'm wondering what the boost profile looks like on that thing from 2000-4000 RPM where most of your acceleration winds up being. I'd love to have a supercharger or something that could give mine about 3-5 p.s.i. boost, mostly making up for ambient pressure loss when operating it at 5000-9000ft elevation most of the time.