Reply to "Rocker Arms"

I can discuss roller rockers... I am running a set of ancient Harland Sharp aluminum roller rockers that I bought used off a Mustang racer....in 1985. Roller rockers do not generally increase horsepower; what they do is reduce sliding friction and thus drop engine oil temperatures. Some sources say oil temps will drop up to 15F degrees with full roller rockers. The low-friction rolling action is both from the needle bearing pivots on the rocker std and from the roller that contacts the valve stem. But all is not roses- at low speeds, the roller on the arm, which is NOT a bearing but a simple tool-steel-roller-on-steel-pin, will still slide across an occasional valve stem. And if you constantly over-rev the engine, valve float will hammer a flat spot on the steel roller, making the sliding action constant. So carefully examine any swap-meet roller rockers you might find. Good roller rockers are rebuildable- the pin comes out with a tiny snap-ring and new rollers and needle-bearings are available from the mfgrs. I had one flat-spotted roller on my used Sharp rockers, which I fixed cheaply. Lower cost roller rockers have rivited pins that are NOT rebuildable. Even cheaper 'roller rockers' are stamped steel with a standard ball-or sled- pivot on the stud and the usual non-bearing roller contacting the valve stem. These are nearly as high-friction as OEM rockerarms and IMHO are useless with hi-lift cams & matched springs. A recent HRM engine build BURNED UP a brand-new set of these rockers during their first dyno run.
IMHO, the best full-roller rockers available are stainless steel units; as it turns out, the protruding arms of the rockers are the critical weight items, not the overall weight, and ss rocker arms, which are much stronger than aluminum ones either extruded or forged- are virtually the same weight as aluminum. So the engine's rev-range is not impacted by running ss rockers. No NASCAR or sprint engine runs aluminum rockers. Besides breakage, to get strength the aluminum ones are bulkier and interfere with oversized springs. Relief-machining rockers for spring clearance often weakens them.
Finally, full-roller rockers for 351-Cs are 1.73:1 lever ratio. Cheaper big-block Chevy units will bolt on without alteration but are 1.70:1 ratio, so you lose 2% of your cam's specified lift. And even greater lift assemblies are available at 1.80:1- about 4% more lift for a given cam. FWIW, valve lift changes are not directly proportional to horsepower; it's more complicated than that. The hi-ratio rocker assemblies are more stressful on everything, so require stiffer valve springs, better pushrods and higher quality cam chains.