Doug T (7/16/2009)
Hi Ted, Is there really much advantage to needle bearings on the shaft of rocker arms? ....I can see the advantage to roller tips on rockers and there may be a very slight friction advantage for needle bearings, but the cost adder to put them in aluminum rocker arms must be considerable.The friction question is something I hope to answer in the near future. I have a set of fully rollerized aluminum 1.6:1 rockers for a Y that I can compare to a set of roller tipped only aluminum 1.6:1 rockers in some back to back testing. Based on some of the scuffing that takes place in the rocker arms that are not rollerized at the shafts, there is obviously some drag taking place. Testing may or may not pick up the difference depending upon just how much difference there actually is. But there are sixteen rockers being dealt with and the higher the valve spring pressures become, then the more the drag potential that can be present. I’ll add that any reduction in rocker arm drag is expected to prolong lifter life and potentially also help in raising the rpm capability.Cost is subjective. Many of the roller rockers being sold now at bargain basement prices are not fully rollerized but are instead bushed at the trunions. Most buyers of these assume there are fully rollerized without realizing they are not. In this case, you get what you pay for. If I can find another 2-3 HP at the rockers by being fully rollerized, then for me it’s worth it.
Don Woodruff (7/16/2009)
Ted: would it be possible to get rocker ratios in the 1.7 to 1.8 ratio range?This hasn’t been proposed before so it’s something that can be asked. But I suspect that unless there’s a demand for several sets, it’s a request that many not be fulfilled. Up till now I’ve been getting by with 1.6:1 rockers on the Y engines as that’s all the lift at the valve I can get away with and still keep cylinder wall notches above the top ring land. These same 1.6:1 rockers have been extended out to 1.67:1 ratio simply by using as long as possible pushrod with them. But having the larger aforementioned ratios available does bring up some interesting possibilities in reducing the lobe lift while having faster valve acceleration rates and still achieving the same gross valve lifts.
Lorena, Texas (South of Waco)