Would you believe us if we told you that you could put 15-17 more horsepower to the wheels with rocker arms? We were a little skeptical until we soaked up the complete details on how possible this feat really is.
If you haven't already heard, Crane Cams has recently released its line of LS1 Gold Race Rocker arms, featuring the all-new Quick-Lift technology. Unlike other rocker arms, the Quick-Lift rocker arms continuously change the ratio. In the words of Crane Cams, "As a rocker arm alternates between the valve closed position and the valve open position, the pushrod seat and the valve tip contact point operate through arcs, which are determined by their distance from the point of rotation." Meaning, the arcs have two varying radius points, which result in the changes of the rocker arm ratio as it travels through its cycles.
According to Crane, depending on the rocker body shape and the pushrod seat location, the changes can be quite substantial. For example, a stock 1.7:1 (advertised ratio) LS1 rocker actually pushes the valve off the seat at a ratio of 1.54:1, and as the pushrod seat rises on the valve opening cycle, the effective rocker ratio finally rises to 1.69:1 at 0.280-inch lobe lift (0.473-inch valve lift). Keep in mind that the valve lift at any point in the lift cycle equals lobe lift multiplied by rocker arm ratio.
By contrast, Crane Cams' Quick-Lift 1.7:1 ratio rocker arms get the valve off the seat at a ratio of 1.79:1 and by about 0.175-inch lobe lift (0.300-inch valve lift), they cycle to a 1.72:1 ratio that is maintained through the rest of the lifter travel until the lifter is within 0.175-inch of returning to the base circle. This unique design has major benefits, such as allowing a greater influx of air into the cylinders by creating a larger lift at every point of the lift curve earlier in the lift cycle and then by maintaining the lift longer throughout the cycle, all the while maintaining the same seat-to-seat timing. More specifically, it can literally emulate a larger cam without having to deal with the drivability issues of a radical camshaft.
Another important aspect of the Quick-Lift rockers, is that even with the higher, effective rocker ratio, as the valve is returning to the seat from 1.79:1 to 1.54:1, the Quick-Lift design allows lower seat pressures. Consider 140 pounds of seat pressure with the stock rockers. In order to control the lifters at high rpm with a fairly aggressive cam lobe, you'll need a 216 pounds of seat pressure (140 pounds x 1.54 ratio = 216 pounds) operating on the lifter with the stock rockers. With the Crane Quick-Lift design, the 216 pounds operating on the lifter can be achieved with only 121 pounds of seat pressure (121 pounds x 1.79 ratio = 216 pounds). And what you may not know is that most other aftermarket rocker arms for the LS1 family have body geometry very similar to the factory-equipped rockers.
It's hard not to appreciate the amount of research and development that has gone into the Quick-Lift rocker body design. Nevertheless, if you're still questioning the real-world gains, then you'll be happy to know that Crane is more than willing to share its R&D results with you directly. Fire up the home desktop and head over to www.cranecams.com. Once there, click the hyperlink addressing the "Street Shark" project, and you'll be taken through each phase of the buildup with real-world dyno results after every modification. It's a fine example of a relatively mild commuter LS1 that gets driven over 100 miles per day and is packing 400 horsepower at the wheels! And if that isn't enough, rest assured knowing that we'll once again fire up our GM Performance Parts LS1 crate mule and comparing notes real soon. Further, we'll be doing a real-world test on these rockers as well as other Crane valvetrain parts in our 5.3L Silverado--hopefully in time for next month's issue.
The Ultimate LS1/LS6 Valvespring Compressor
If you've ever attempted to change valve springs with the engine in the car, then you know how arduous that can be, especially when you're leaning over an F-body for hours on end. Crane has devised this simple yet ingenious tool (PN 99472-1) to make the job easier. Constructed of CNC-machined steel, this valvespring compressor is operated by a box or open-end wrench, and allows you to swap springs in about an hour. A valvespring compressor for all conventional '57-96 small-block Chevy engines (PN 99473-1) is also available.