With limited dyno time left in the day, we swapped out the stamped-steel 1.5:1 rockers for a set of Comp Cams 1.6:1 Magnum-style roller pieces. This added nearly 0.300 inch of lift to the intake and exhaust valves, while increasing the duration of the valve by nearly 2 degrees. All carburetor jetting and timing variables remained the same as we pulled our engine to a new peak reading of 371 hp at 5,900 rpm and 382 lb-ft of torque at 4,600 rpm. The additional lift and duration made only a small difference in the torque curve but raised the peak rpm of the engine by nearly 400, to deliver an additional 12 hp up top. While the rocker swap delivered a relatively small kick in the pants compared to the heads, we knew there would be more power with a better cam grind.
We were now on a mission for ultimate power, and up next was a new bumpstick from Comp Cams. The grind of choice featured 0.470/0.470-inch intake and exhaust lifts with a 1.5:1 rocker ratio and 224/224 degrees of duration at 0.050 inch lift on 110 LSA. The hydraulic flat-tappet piece is a mild choice, picked to help improve street power without affecting the engine's idle vacuum. Once the fuel lines were hooked back up we started the engine and repeated the break-in procedure. The timing remained at 36 degrees total, and the jetting was still good, showing air/fuel readings of 12.8:1 at peak torque. After a quick look over all the vitals, we ran the engine across its power curve. With new readings of 385 hp at 5,600 rpm and 407 lb-ft at 4,200 rpm, we were pleased to see additional improvements to the tune of 6 hp and 29 lb-ft over the factory cam with 1.5:1 rockers. What's interesting is that our new single-pattern cam increased the horsepower at a lower peak rpm point while also significantly improving the torque across its entire power curve.
The Final Word
Adding more camshaft duration would have raised the peak rpm point up into the 6,000-rpm range and perhaps made 400-plus horsepower, but idle vacuum would have been sacrificed along with some torque. Our factory long-block with either stock or high-performance GMPP heads delivered 13 inches of idle vacuum at 800 rpm, and our new camshaft delivered more power while sacrificing only a half inch of idle vacuum at the same rpm. We set out to build a solid street engine using readily available performance parts and increased our total power by 70 hp and 58 lb-ft. It just goes to show that with the right parts and help from some of today's leading high-performance manufactures, ultimate street power is only a phone call away.