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Old 01-03-2013, 07:01 PM   #1362
Patrick Olsen
NASIOC Supporter
Member#: 120
Join Date: Jul 1999
Chapter/Region: AKIC
Location: Where the Navy sends me...
1997 Legacy 2.5GT
1996 Impreza coupe


Originally Posted by Marnix View Post
As long as the low lobe and high lobe are increased by the same amount (ie. the difference in base circle stays the same) then there is no issue. My feeling says that a bit bigger difference would be acceptable, if the base circle is almost the same I guess there would be difficulties with the system switching from low to high lobe (then there would not be enough 'time' to push the plunger in the bucket to lock the bucket).
OK, at home now, so I can look at the FSM specs.

Cam base circle diameter: High - 32mm; Low - 31.84mm
Cam lobe height: High - 42.14mm; Low - 38.19mm or 35.49mm

You raised an interesting point that I hadn't thought about - ensuring there's enough time for the lifter to lock into the high lift mode. So if you increased the duration of the high lift lobe by a lot, but didn't really touch the low lift lobe duration, the two lobes might not have enough time on the back of the lobe to get the plunger to be pushed back in and allow the lifter to lock into high lift.

And the factory specs do have a little bit of a difference in the base circles, I suppose just to keep the low lift lobe from riding on the lifter when it doesn't need to.
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