Re: Roller Lifters

["James J." <m1garand@speakeasy.net>]

A roller-cam is typically more agressive, with regards to rise and fall 
time.  I believe that a roller-lifter could easily work on a less 
agressive profile (stock cam), for the same reason a highly tuned 
autocross car can easily drive on the interstate highway system as well 
as a lazy Lincoln or Caddy can, but the reverse is not true.  Because 
the bottom of a roller lifter is radiused (and rolls) it can approach a 
steep slope with aplomb, but nothing prevents it from also traversing a 
cam that is worn to the point of being nearly flat.  A flat tappet is 
far more limited in the profile of cam it can approach.  A lobe that a 
roller could glide over could conceivably slam into the side of a 
conventional lifter and sieze up the entire valvetrain.
So part of my original question was:  Since a roller lifter can handle a 
normal cam, does the reduced friction of  a roller lifter offer any 
performance/durability gains over a regular lifter on the same cam?  If 
it frees up another 10 HP, or allows me another 30K miles before a 
regrind, for example, I may look into developing the idea further.  It's 
well established that roller rockers free up a few ponies and increase 
the life of the valvetrain, and they only introduce friction  during one 
stroke of the 4-stroke cycle.  Cam lifters are constantly intruducing 
friction as the cam is always rotating underneath them, and I believe 
the contact patch is much larger, so it seams like an area for 
investigation.  Then again the oil-film on the cam lobes could reduce 
friction to levels below what the rocker tips generate moving across the 
valve stem, if that area has worse lubrication.  I honestly don't know, 
which is why I was asking.  Perhaps Detroit concluded that it didn't, or 
that it did, but wasn't cost effective.

JJJ

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