The V8 Owners Forum -

unless of course you are going for a roller cam with a profile that is more radical than a flat tappet cam could achieve in which case you might want stronger springs, but still. Hummm.....

The ramp angle on a roller is physically much steeper than on a flat tappet cam and only very high spring pressure can keep the lifter on the cam lobe. This itself is only possible due to a reduction in friction with the roller wheel arrangement. Interestingly if you lay a roller cam down side by side with a flat tappet cam of the same spec the lobes of the roller look much "fatter" in comparison. They are physically much fatter but the geometry of the roller lifter arrangement means that the actual difference in figures is not as big as you would think looking at the cams. The roller lifter experiences much greater side loads that the flat tappet design and the smaller the wheel in the lifter the worse the problem gets.

HairbearTE wrote:The ramp angle on a roller is physically much steeper than on a flat tappet cam and only very high spring pressure can keep the lifter on the cam lobe. This itself is only possible due to a reduction in friction with the roller wheel arrangement. Interestingly if you lay a roller cam down side by side with a flat tappet cam of the same spec the lobes of the roller look much "fatter" in comparison. They are physically much fatter but the geometry of the roller lifter arrangement means that the actual difference in figures is not as big as you would think looking at the cams. The roller lifter experiences much greater side loads that the flat tappet design and the smaller the wheel in the lifter the worse the problem gets.

Which is the whole advantage of the roller cam!!!

I wonder why they haven't developed one for a DOHC engine? It is definately possible as I did a project on it once and developed a design that would work. Would need much taller cylinder heads though. Seems like current designs are going the way of follower valves though....

crayefish wrote:

HairbearTE wrote:The ramp angle on a roller is physically much steeper than on a flat tappet cam and only very high spring pressure can keep the lifter on the cam lobe. This itself is only possible due to a reduction in friction with the roller wheel arrangement. Interestingly if you lay a roller cam down side by side with a flat tappet cam of the same spec the lobes of the roller look much "fatter" in comparison. They are physically much fatter but the geometry of the roller lifter arrangement means that the actual difference in figures is not as big as you would think looking at the cams. The roller lifter experiences much greater side loads that the flat tappet design and the smaller the wheel in the lifter the worse the problem gets.

Which is the whole advantage of the roller cam!!!

I wonder why they haven't developed one for a DOHC engine? It is definately possible as I did a project on it once and developed a design that would work. Would need much taller cylinder heads though. Seems like current designs are going the way of follower valves though....

I would say that the reason rollers haven't been used in DOHC engine is probably because the whole developement of the roller cam came about as a result of the need to get more valve "curtain area" open time per cycle in engines that are hampered by 2valve design and/or bad heads - i'e. old V8's. A modern 16v DOHC design has as much valve as it needs. That is my assumption.

Yeah that is probably true on a passenger car, but what about race engines? Its a half way step to F1 pneumatic valves in terms of lift profile.

Interesting Discussion. I have seen these and thought I would add it to see what you all thought.

Set of Roller Lifers for Rover V8 by Crower

https://www.crower.com/lifters/lifters- ... -body.html

They look very like mine,
I got mine from Triumphroverspares in Australia