Hey Full Force Tim
12-20-2016, 04:19 PM
#1
Hey Full Force Tim
This is a good read from another thread. Would have been good on your "Short duration high lift longevity" thread.
M AY 2015
7
FEATURE
PERFORMANCE TECHNICIAN
Once you’ve made the move to roller lifters, your choices and options get better. Obviously, friction is reduced because you’re rolling over the lobe instead of dragging over it. Where the flat lifter is velocity-limited, the roller lifter is acceleration-limited. You can only achieve so much rate of lift before the pressure imposed by the wheel on the lobe initiates contact failures. The pressure angle is the angle formed as the roller impacts the lobe. The advantage of a roller is that you can shorten duration while maintaining high lift, but in doing so the wheel almost gets driven into the side of the lobe on the opening ramp. By necessity, the first point of contact has to be something above the centerline of the cam core, otherwise the lobe just tries to knock the wheel off of the lifter. If you look at some of the photos, you can see where the roller wheel marks the lobe. There is considerable side thrust generated and this will be seen as increased wear in the lifter bushing, often in an hourglass pattern, wide at the top and bottom and at or near specification in the center of the bore. Using a larger diameter cam core helps reduce pressure angle, as does using a roller lifter with a larger wheel. If you use a larger wheel, remember that while the lift will be unchanged, a larger wheel will increase the effective duration of the cam, opening the valve earlier and closing it later. You will need to account for this when you talk to your cam grinder
http://performancetechnician.com/pdf...a-Lifter-2.pdf
M AY 2015
7
FEATURE
PERFORMANCE TECHNICIAN
Once you’ve made the move to roller lifters, your choices and options get better. Obviously, friction is reduced because you’re rolling over the lobe instead of dragging over it. Where the flat lifter is velocity-limited, the roller lifter is acceleration-limited. You can only achieve so much rate of lift before the pressure imposed by the wheel on the lobe initiates contact failures. The pressure angle is the angle formed as the roller impacts the lobe. The advantage of a roller is that you can shorten duration while maintaining high lift, but in doing so the wheel almost gets driven into the side of the lobe on the opening ramp. By necessity, the first point of contact has to be something above the centerline of the cam core, otherwise the lobe just tries to knock the wheel off of the lifter. If you look at some of the photos, you can see where the roller wheel marks the lobe. There is considerable side thrust generated and this will be seen as increased wear in the lifter bushing, often in an hourglass pattern, wide at the top and bottom and at or near specification in the center of the bore. Using a larger diameter cam core helps reduce pressure angle, as does using a roller lifter with a larger wheel. If you use a larger wheel, remember that while the lift will be unchanged, a larger wheel will increase the effective duration of the cam, opening the valve earlier and closing it later. You will need to account for this when you talk to your cam grinder
http://performancetechnician.com/pdf...a-Lifter-2.pdf
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