Roller-Rocker Test
There was a time when aluminum roller rockers were a status symbol of only the most elite road race or drag race engine. Today, you have to look for a reason not to run a set, especially when you read this test that originally ran in the January '01 issue. Here, the guys at Westech bolted a mild 350ci small-block Chevy to the dyno equipped with a Comp Cams Xtreme Energy 268 hydraulic flat-tappet cam, stock stamped-steel rockers, a set of TFS 23-degree aluminum heads with 2.02/1.60-inch valves, an Edelbrock Performer RPM intake, a Barry Grant 750-cfm Speed Demon carb, and a set of 158-inch headers feeding into a 212-inch Flowmaster exhaust.
The test was a simple comparison of stock stamped-steel 1.5:1 ratio rockers to a set of Comp Cams Pro Magnum steel 1.5:1 and 1.6:1 rockers and a 1.65:1 ratio Comp High Energy aluminum rockers. The following chart reveals the power increases that generally track right along with the ratio. Where else can you bolt on something simple like a set of rocker arms in about an hour that will add an average of 15 lb-ft of torque and 13 hp? Granted, not all engines will respond as this one did. Basically, a bone-stock set of heads would probably not have gained as much as this combination. Clearly, the better cylinder heads that flowed 250 cfm at 0.500-inch lift offer proof as to why this test was successful. That's probably the lesson here--that stock heads will not benefit as much from more lift compared to ported or aftermarket heads. This test does point out the power of a well-matched package of cam and valvetrain.
Budget Cam Swap
Not all of our testing involves high-end, mega-dollar stuff. We've also tested some very easy-on-the-wallet deals like this flat-tappet cam swap for a mere $245.67, including the cost of the gaskets. We started with a typical 350ci small-block Chevy equipped with a stock-style flat-tappet hydraulic cam. Next, we jumped in with an Erson TQ40H mild flat hydraulic cam and lifter package along with a new set of springs to replace the tired originals. With the engine on the dyno at Westech, it peaked at 326 hp at a mere 4,700 rpm with impressive torque at 398 lb-ft at 3,700 rpm. The valvesprings were also clearly overworked even with the stock cam, so the swap included a set of new Erson single-wound springs as well. The Erson cam added a solid 23 degrees of duration on the intake side and 26 degrees on the exhaust side, both measured at 0.050-inch tappet lift. The Erson also added a whopping 0.082 and 0.062 inch of valve lift. The combination of the two points, plus some overlap, are clearly the reasons why this inexpensive cam swap was worth an honest 77 peak horsepower. Because the stock cam made such good torque, the bigger cam actually lost torque between 2,000 and 3,000 but compensated with a ton more power between 4,000 and 5,900 rpm. The best indicator of all is the 44hp average power increase over the entire rpm band.
That tells you this is a substantial gain. When you can get all that for under $250, that's a win, baby. Roller rockers also require more careful attention to pushrod length since the roller tip contact pattern is much smaller than the wide pad of a stamped-steel rocker. Guideplates are also virtually a necessity to ensure the roller tip is accurately centered over the valve stem.
 The beauty of a mild hydraulic...  The beauty of a mild hydraulic camshaft is that even a conservative cam swap will generate an excellent power return for a modest investment. Measured in dollars per horsepower, this 77hp gain cost a mere $3.19 per horsepower. |  Dyno-testing is not quite...  Dyno-testing is not quite the same thing as testing in the car, but we included mufflers to get the results closer to real-world examples. | |