Jim Smart
October 21, 2010
Photos By: Mark Jeffrey

Port Work
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.

Photo Gallery

View Photo Gallery

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.

Dyno Results

Pull One
Edelbrock Performer RPM Air Gap intake manifold, 830-cfm Holley 4150, and 1.6:1 Trick Flow Specialties rocker arms
RPMHPTQ lb-ft
3,800264.1365.0
3,900272.8367.3
4,000282.3370.6
4,500326.8381.5
5,000391.8411.6
5,300420.3416.5
5,500432.3412.8
6,000455.6398.8
6,500479.2387.2
Pull Two
Switch to 1.7:1 Comp Cams Magnum rocker arms with Edelbrock Performer RPM Air Gap intake and 830-cfm Holley 4150
RPMHPTQ lb-ft
2,800181.2340.0
2,900189.8343.8
3,000200.4350.8
3,500263.2395.0
4,000319.3419.2
4,500360.1420.2
5,000411.5432.2
5,100422.5435.0
5,200430.7435.0
5,500445.9425.8
6,000471.3412.6
6,100475.4409.3
6,200479.1405.8
6,300482.7402.4
6,400485.2398.1
Mark tried different carburetor spacers to see what happens to horsepower and torque. With the Parker manifold, there wasn't much difference because the manifold has a natural bend toward velocity right out of the box with just the right amount of plenum for high rpm use.

PULL 3
Parker single-plane, long-runner intake manifold, 830-cfm Holley 4150, and 1.6:1 TFS rocker arms

RPMHorsepowerTorque lb-ft
3,000186.4326.3
3,500240.9361.4
4,000299.5393.3
4,500347.3405.3
5,000402.3422.6
5,200421.9426.1
5,500443.1423.1
6,000471.8413.0
6,100476.7410.4
6,200481.0407.5
6,300485.6404.8
6,400490.7402.7
6,500495.1400.0

PULL 4
Parker intake manifold w/1.7:1 Comp Cams Magnum rocker arms

RPMHPTQ lb-ft
3,000170.2297.9
3,500238.2357.4
4,000299.9393.8
4,500346.5404.4
5,000401.8422.1
5,200420.9425.1
5,300429.0425.1
5,500444.8424.7
6,000475.9416.5
6,500502.4405.1