For our Budget 347, Mark port-matched the intake manifold and cylinder heads to achieve smooth airflow. This is one of the single greatest steps you can take when building a street driver small-block. Port matching and cleaning up the runners yields abundant airflow, as proven by our chart. Mark achieved a whopping 26.45 percent and 81.7 cfm on his best runner with port work. He also cleaned up the plenum, which improved flow.
What Is Rocker-Arm Ratio?
There are two kinds of lift-lobe lift and valve lift. Lobe lift is maximum lift or rise at the cam lobe. For example, if lift is 0.450-inch lobe lift, the lobe itself gives us 0.450-inch (nearly 1/2-inch). Valve lift is what the cam lobe and rocker arm combined give us via the pushrod. If we're running a 0.450-inch lift cam with a 1.6:1 rocker arm, we're getting 0.720-inch or nearly 3/4-inch. Rocker ratio-1.6:1-takes 0.450-inch cam lobe lift and multiplies it 1.6 times. When stepping up to a 1.7:1 rocker ratio, we're taking cam lobe lift and multiplying it 1.7 times.
Parker single-plane, long-runner intake manifold, 830-cfm Holley 4150, and 1.6:1 TFS rocker arms
Parker intake manifold w/1.7:1 Comp Cams Magnum rocker arms