060” if conservative) piston-to-valve clearance before running the engine." After installing longer-ratio rockers, always check that the engine has adequate (.040” minimum. 040” valve lift to the engine, depending on the cam lobe lift of the camshaft. Increasing the rocker arm ratio increases the lift at the valve without changing the camshaft. Two increased rocker arm ratios that come to mind are a milder Ultima 1.675 and 1.690, Crane Cams 1.725, and JIMS 1.745 ratios. The rocker arm ratios for earlier Harley-Davidson’s are 1.4 to 1984 Shovelheads, 1.5-1965 Panheads, and 1.000 direct ratio for 1936 to 1947 Knuckleheads. The trick is to increase the rocker arm ratio from the stock 1.6 to 2000 Evolutions and 1999-to-present Twin Cams. ![]() "I want grunt power in the lower rpm ranges, where I use my bike the most.ĭo not worry, there will still be lots of power in the top end especially have if there are higher flow aftermarket heads or if the stock heads are ported and polished. At what point does the rocker arm ratio become a bigger factor when cam lobe height reaches a certain lift.a limit for valve opening based on spring height, and clearance between valves and piston tops, and valve to valve clearance?
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