Howdy back Dave:
The math is quite simple. If the lift on the cam lobe is .300" a 1.5 rocker arm ratio multiplys that amount by half or .300" X 1.5" = .450". IF you were to change to a rocker arm with a 1.60:1 ratio lift would be .300" X 1.6 = .480" OR a difference of about .030" lift increase. .030" is about the thickness of a match book cover. You can gain that much by backcutting the valves, which also lightens them. Lighter is better.
Increased ratio lift does add stress to the whole valve train system, so the question should be can your engine use the extra lift or is it just wasted motion? Most log heads cannot effectively use lifts much beyond .400". The 1.6:1 ratio does not open the valves any sooner or change closed duration. It will slightly alter durations at .050" of valve lift because it has to open the valve farther in the same amount of time.
Most performance cams have adequate lift using the 1.5:1 rockers. Lift is lift as far as air flow is concerned. You job is to figure what you need and how best to get it.
Other advantages of adjustible roller-tipped rockers are; less friction, less side stress on the valve stems, hydraulic lifter pre-load adjustment.
Full roller rockers, rollers on the shaft and on the tip, offer less friction at all contact points.
Either roller tipped or full roller rockers are available in 1.5:1 and 1.6:1 ratios.
For high rpm work and sustained high rpms roller rockers should be considered essential. They will likely not add much in HP. They will add reliability and endurance. AND they are super cool. It's too bad they have to be covered up with the valve cover.
The downside to either is $$$$$.
I prefer to get the increased lift built into the cam and use 1.5:1 rockers. However, if I were not changing to a performance cam then 1.6:1 rockers is an easy, but not cheap, bolt-on increase. Of course you have to have the complete coordinated package to take advantage of the lift increase.
If you decide to go for the 1.6:1 rockers be sure to check for clearance between the bottom of the retainers and the valve stem seals, and that the valve springs do not bind.
That's my two cents, for what it's worth.
Adios, David
