GM Performance Parts 350 H.O. Crate Engine - Project Humble Pie, Part II

When using any 1.6:1 ratio rocker arm with Vortec heads, you must increase the length of the pushrod slot in the heads to prevent the pushrod from hitting the head. In this case, we drilled the pushrod holes from 5/16 to 3/8 inch, but this does require removing the heads from the engine.

The GM Performance Parts Bow Tie roller rockers utilize a shorter slot in the rocker body that increases strength by 30 percent yet still allows valve lifts of up to 0.575-inch lift. These are also self-aligning rockers that do not need a pushrod guideplate. The roller tip uses small guides on both sides of the tip to keep the rocker centered on the valve.

The 350 H.O. uses a post-'86 one-piece rear main seal block that is also configured for roller cams, so the block is already machined for the cam thrust plate and the lifter valley utilizes taller lifter bores that can use the OEM roller lifters. These lifters require the OEM style tie bars and one-piece tin "spider."

Keep in mind that all the modifications so far have been in conjunction with a set of very stock Vortec iron heads with 1.94/1.50-inch valves and a mild 9.1:1 compression ratio.

Once bolted back up to Ken Duttweiler's Digilog dyno, the 350 H.O. responded to the roller cam swap with a major increase in torque and horsepower, churning out a respectable 401 hp at 5,600 rpm and 428 lb-ft of torque at 4,200. Plus, it idles at 15 inches of vacuum.