PeachParts Mercedes-Benz Forum - View Single Post - interference vs non-interference engines

Angel · #13 06-30-2008, 11:31 PM

To answer the OP - my impression is that any manuf. can build a non-interference engine...up until recently.
Obviously, if toyota did it, then its not an engineering impossibility, I figured that its more a design/cost thing than than anything else. The Toyota engineers were told to design an engine that is non-interference. The designers of the Altezza motors were not.

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.

I say "up until recently" because the bar has been raised so high for engines as of late, that its probably tough to build an engine efficient enough for modern power/emissions standards that is not non-interference. Okay, Toyota can do it for bread-and-butter 4cyls, can they do it for 300hp truck V8's ? (I don't know)
From what I remember - back in 1990, the 2.0l 16v VW 4cyl made 130hp- it got 30mpg if you didnt beat it too hard. My wives 1997 neon had a 2.0l 4cyl, 16v, better emissions (OBDII), made 130hp and got 36mpg with an automatic transmission. This isnt a good apples to apples comparison, but I think we can agree that engines have come a long way in the last 5 or 10 years, and if someone tried to stuff that 16v 2.0l vw motor in a car today, it'd never sell. (not that I don't love old VW 16v's....)

As to the maintenance requirements - I don't think that manufacturers care as long as the engine will make it to 100k (the req'd US emissions warranty) with no trouble. After 100k, the manufacturer gains nothing from having a long lasting-chain vs. a belt that needs replacing.

-John