COMP’s new short-travel lifters can give your engine the best of both worlds: the reliability and installation ease of a hydraulic roller, and the power and rpm range of a solid roller.
In the mid 1980s, when hydraulic roller lifters came into wide-spread use, they offered many advantages over flat-tappet hydraulic and flat-tappet solid lifters. From a wear standpoint, they pretty much lasted forever, and for performance they offered a lot more area under the curve than flat tappets. But even then, the solid roller lifters used in race engines trumped the hydraulic roller in most areas, especially for rpm range, and flat-out power.
Hydraulic lifters employ a plunger that places a buffer of engine oil between the lifting body, and the pushrod. As the lifter follows the lobe, the oil absorbs the impact of the ramp, thus reducing valvetrain noise and wear in normal circumstances. It also allows friendly tolerances in valvetrain lash for easy installation and low maintenance.
The fly in the ointment is that as the power level increases, hydraulic lifters become increasingly inadequate. High valve spring pressure, higher rpm, and higher lift values place the plunger and the oil buffer under it in duress, with the result often being a plunger collapse. That’s exactly what happened to the 469-ci big-block in our ’68 Chevelle project car. Equipped with a COMP Cams Big Mutha Thumpr camshaft, our stock-style hydraulic roller conversion lifters simply gave up the ghost one night on the highway. We were lucky that our collapsed lifters didn’t beat up the rest of the valve train or bend any pushrods.
We looked around for a solution, and discovered COMP’s new line of short-travel lifters. COMP offers these for most GM engines, including LS, small-block, and big-block Chevy. Without delay, we ordered a set for our big-block (part No. 15854-16, $536.95). What makes them unique is that they still offer the hydraulic mechanism with the plunger and oil buffer, but with a much reduced plunger travel. Where most hydraulic lifters have .200-inch of travel, the COMP piece has just .012 inch of travel. In our case, that would mean high-rpm track (or street) use would not result in the plunger collapsing, resulting in a loss of two hundred thou in valve lift. That’s equal to a boatload of flow at high rpm. As a hydraulic lifter, we wouldn’t need to fuss with setting hot valve lash, and revisiting the operation on a regular basis.
About the only issue we found with the swap is that it requires a .100-inch shorter pushrod when compared to our hydraulic roller conversion lifters we had been using.
When the swap was completed, we noticed a major seat-of-the-pants increase in power. The other thing we observed is that the big-block has a different tune—one that’s more like a solid-roller race motor. Gone is the clatter that we experienced after running the engine hard (the result of the plungers bleeding off oil and leaving mondo lash). Fortunately, we have a baseline chassis dyno test of the Chevelle with the original lifters. This is going to allow us to go back with the short-travel lifters and get a new power curve for comparison. We’ll be publishing the whole story soon, most likely in the February or March issue!