More Lift, More Duration

When we left this fat ol' mutt last month, its motor was fixed with the foundation for a spicier camshaft. A Crane rocker-arm kit (1.8:1, dual valvesprings, stouter pushrods, etc.) and the beginnings of a deep breathing apparatus (K&N cold-air intake and Bassani after-cat system) laid the groundwork for a Crane cam featuring more lift and duration than the stock camshaft. Although our Silverado is equipped with a 5.3L engine (325ci), this stick can also be applied to a 4.8, 5.7, or a 6.0L engine with similar results.

Roger Vinci specified the grind (HR-210/ 3241-2S-12 2A) because it works well with the stock LM7 aluminum cylinder heads (61.15cc combustion chambers, 9.5:1 compression ratio, 200cc intake-port volume, 70cc exhaust-port volume, 1.89-inch intake valve, 1.55-inch exhaust valve) and the OE cast iron exhaust manifolds that remain intact for the initial phases. This grind also promises compatibility with freer-breathing heads, tubular headers, high-flow catalytic converters, and the roots-type supercharger that will likely complete the final combination. With a 1.7:1-ratio rocker arm, the specs are 0.551-inch lift for both valves and 210/218 degrees of duration at 0.050-inch.

Ancillary equipment for the cam swap was Crane's adjustable dual-roller timing set (PN: 144984-1), including billet steel sprockets, oil pump spacers, and instal-lation hardware. This tough ensemble ensures that the timing gear will stay where it should be. Without it, the worst case would be that the cam slides back in the block, causing the lifters to hit the lobes next to them as well as the cam-bearing journals, chipping the lifters and the sides of the lobes. Further, the cam sprocket can be adjusted to retard or advance timing by five degrees, but Vinci's Greg Warner installed our camshaft straight up.

As you've noticed, gasoline prices have become a concern, notorious in some parts of the country. In mid-May, 93-octane was selling for $2.26 a gallon in central Florida; in southern California during the same period, we paid as much as $2.95 for 91, the highest rating available there. We wondered how this normally aspirated engine equipment would affect the overall picture. Without getting too involved, our strictly around-town numbers are something like 14 mpg; a mixture of super-slab and stoplights puts the tally a bit beyond 18, and that's without regard to the throttle. Of course, a large part of this has to do with the engine design; the stuff we put to it has simply magnified its superiority.

On the visceral side, the engine now has a loping idle that smoothes out some-what as the engine reaches operating temperature. It sounds like the old days, and elicits that same bad-boy emotion from a middle-age psyche and stirs some cayenne in the blood. As designed for mid- and upper-range response, the cam is a bit on the lazy side under normal throttle, but when you push the pedal halfway down, the engine zings. Mat the throttle and it goes right to six grand with a head-turning howl. Passing up a semi on a two-lane in the bug-blown, tar-black Florida night is no more difficult than popping a tallboy by the pool.

So far, the engine enhancements have provide these corrected maximum outputs: stock: 289.4 lb-ft, 236.7 hp; Crane rocker-arm kit: 299.6 lb-ft, 255.9 hp; K&N and Bassani exhaust: 318.9 lb-ft, 273.5 hp; Crane cam: 324.2 lb-ft, 304.7 hp. Next, well be looking for more low-end, as well as an increase in top-end performance with aftermarket cylinder heads, tube headers and high-flow catalytic converters. Think you can stay awake?