391ci Small-Block - Tech - That's Solid

Barkley chose a big Lunati solid roller cam with 249/255 degrees duration at 0.050 inch for his 391 small-block to deliver a big, broad power curve. On the dyno this cam helped produce more than 500 lb-ft of torque from 4,700 to 5,400 rpm. For an engine that lives mostly on the street, a smaller hydraulic roller with less duration might be a better choice because it offers quieter operation, almost never needs a valve adjustment, and its lower amount of duration (less than 225 degrees at 0.050 inch) typically helps increase cylinder pressure and improve low-speed torque.

These seasoned AFR heads were retained in order to keep the budget in place. Back in the '90s, when these were originally designed, the bigger-than-stock 190cc intake runners and good flow characteristics enabled them to flow 260 cfm on the intake side at 0.500 inch lift. Even by today's numbers, they are still respectable and produced killer numbers on the engine dyno.

The new Lunati solid roller cam called for higher spring pressures over the original Beehives, so we swapped them for a complete Lunati kit with matching valvesprings, retainers, and keepers. Anytime a camshaft is replaced, it's best to install the manufacturer's valvespring kit designed to match the grind and rpm range of the camshaft. If not, operating rpm may be limited from valve float.

When replacing a camshaft, it's always a good idea to also install a fresh timing chain. Typically, an old timing chain will have wear on the cogs and will stretch, which may cause the cam timing to move during engine operation. This new double-roller chain from Lunati is accurate and allows you to set the sprockets to provide a maximum advance/retard at camshaft of 4 degrees and a maximum advance/retard at crankshaft of 8 degrees.

The Lunati Ultra Series dual valvespring kit we installed included chrome-moly retainers and locks. These springs provided 220 pounds on the seat when installed to a 1.90-inch height, and the open load was 550 pounds at 1.250 inches. Dimensionally, they measured 0.706 inch id and 1.514 inch od.

When we first installed the new springs, we learned that the existing spring pockets in the cylinder heads weren't large enough in diameter to allow the springs to fully seat. To remedy this, Bob Vrbancic disassembled the heads and enlarged the pockets.

To activate the valvetrain, we installed Lunati pressurized roller lifters with a vertical bar design. An added benefit is that these lifters are also rebuildable.

To actuate the valves we chose a set of these 1.6:1 Scorpion Race Series roller rocker arms with a 7/16-inch rocker stud. These feature added clearance between the retainers and the springs, a needle-bearing fulcrum and needle tip, and a thick-walled adjusting nut. They're made in the U.S. and are available in your choice of blue, red, or gold and in any ratio.

With the valvetrain largely in place, Bob Vrbancic degreed the camshaft to ensure that it was installed correctly. By lengthening an adjustable pushrod, installing it, and running the rocker arm through a trial revolution, he found the pushrod length should be 8.100 inches. The rocker-arm tip should ride from the upper third portion of the valve tip (with the lifter on the cam's base circle) to the outer third of the valve tip (at full valve lift) during this test.

Once the valvetrain was in place and the rocker-arm covers installed, we found that some rockers were contacting the bottoms of the valve covers, so George Vrbancic machined a clearance spot across the ribs on both valve covers.

This Holley single-plane Strip Dominator intake manifold provides large isolated runners aimed directly into each intake port, which provides abundant air/fuel distribution at upper-end engine speeds. The isolated runners also promote a cooler air/fuel charge prior to entering the engine and produce excellent power from 4,500 to 7,600 rpm, which was a good match for the long-duration solid roller camshaft.