I would go roller if you can swing the added $$ Its all about reducing friction
A cam's lobes are designed to do only one thing and that is push the tappet up to open the valve and let it follow the lobe back down to close the valve and try to keep it from bouncing off the seat. Less friction makes more power and will increase longevity on parts a little more. Roller lobes are designed to open the valves with more more area under the curve. As the valve approaches max lift a roller tappet can hold it open longer than a flat tappet. But flat tappet cams might be more capable in the low end power to due to their more aggresive initial opening rates, but their advantage quickly goes away as frictional losses take over vs. roller tappets and the top end power increases as the roller tappets far outweigh the marginal low end advantage.
The savings in frictional losses are minimal, Taylor. As far as longevity is concerned, I have seen flat tappets go over 1,000,000 miles without issue. I think the added longevity argument is not valid. In fact with our engines designed for flat tappets adding much higher mass and pressure will actually speed up wear. You are forgetting about the additional weight of the roller assemblies. This requires more spring pressure, no way around it if you want to control the valves. This additional mass and pressure works overtime on rocker assembly wear. Rollers are much more desirable when the engine in question is turning 7,000-15,000 rpm. There are benefits for cummins engines but they are going to be for the puller on the edge. With our heads flowing so little, the benefits that roller cams bring to the table are almost entirely nullified by the the port designs. Unless you are filling the water jackets and getting a port shape that will take full advantage of high lift roller profiles. Your added hp per dollar is minimal.
Something to think about
custom flat tappet cam $699
custom faced mushroom tappets $96 dollars
Roller cam $1300-$1800
aluminum side cover clearanced for roller tappets $325
roller tappets $649
related hardware $125
tappet bore bushings $149
Machine work for lifter bores $600 -750
Machine work for bushings in block $400-600
Your final cost is $795 vs. a $4000 average. That is an expensive minor friction reduction, unless you have a REALLY nice head.
Final answer, rollers become more valuable as RPM's eclipse 7000 (like in gassers) or you have a head that actually flows air at high lift (like in gassers).
silver 03 we are working on a roller that uses our upgraded cast billet and roller tappets.
Zach
op:
