As it was explained to me:
You tend to get bounce at high RPM, but the hotter the cam, the lower the RPM
required to cause bounce. Why?
A lifter with stock springs can only follow the cam so fast before the cam is
moving faster than the lifter's ability to follow it. There are two factors
that affect this. Lift and RPM.
For a hotter cam, the lifters are moving a greater distance during a very
similar time period (i.e. moving along the cam lobe at a much faster rate). At
some point the cam lobe shape is so high that the lifter simply cannot move
quick enough to follow the contour correctly and smacks down on the cam after
seperating from the cam for a split of a split second. Very rough on both the
cam and the lifter.
As the cam gets hotter, the lift gets higher as well as the lifter speed. It
therefore takes less RPM for the lifter to lose contact b/c the lifter's follow
speed is increased by virtue of the lobe lift.
When it does happen, 1) you get incredible inefficiencies b/c the valves are
open at way the wrong times, i.e. the exhaust valve is incorrectly open at the
same time as the intake, so the piston sucks air from the exhaust as well as
the intake, or the intake is incorrectly open at the same time as the exhaust
resulting in exhausting out the carbs.
I'm not sure if the valve are ever open during a compression stroke, as the
compression probably forces them closed. Can this happen as well?
I think I explained this correctly and clearly. If not, I'm sure the list
will burn my a$$ for it. <grin>
Mike
Jeff Boatright <jboatri@emory.edu> wrote:
> Hey Peter,
I guess I was too brief. Does valve bounce occur at only high rpm,
what does it sound like, and what eventually happens (which parts
break)?
Thanks,
Jeff
PS: The rotor is doing great. Thanks again.
At 2:38 PM -0500 10/25/00, Peter C. wrote:
>Can you say bounce?
>
>Mr.Rogers
>-
>At 02:28 PM 10/25/2000, Jeff Boatright wrote:
>>What happens if you don't install performance springs?
>>
>>At 1:12 PM -0400 10/25/00, mgraziano@mindspring.com wrote:
>> >You can try Elgin Cams at www.elgincams.com
>> >
>> >This is what they have listed.
>> >
>> >AUSTIN HEALY SPRITE, MG MIDGET, AND MINI PROFILES
...
>> >GRIND SEAT .050î CAM LASH APPLICATION
>> >NO. DURATION DURATION LIFT
>> >
>> >67-18 268 222 0.289 I .018 1275 NEEDS PERFORMANCE SPRINGS
>> > E .020
>> >
>>...
_____________________________________________________________
Jeffrey H. Boatright, PhD
Assistant Professor, Emory Eye Center, Atlanta, GA, USA
Senior Editor, Molecular Vision, http://www.molvis.org/molvis
mailto:jboatri@emory.edu
|