Cam and lifter kits are designed in both solid and hydraulic configurations. The hydraulic
The decision-making process when selecting a camshaft used to be little more than answering the question, “How big do you want to go?” At one time, virtually all Detroit engines came from the factory with hydraulic flat tappet cams, and most of the time that was what went back in when building an engine for street performance. Solid flat tappet cams were OEM on some muscle engines, but were generally few and far between, while solid rollers were reserved almost exclusively for serious drag racing machines. Hydraulic roller cams came on the scene in the 1980s, offering yet another popular cam configuration. Today, we see street engines built with all four of these types of cams, and each have their pros and cons. The first decision that needs to be made when selecting a cam is just what kind of cam it is going to be. Here we look at these four cam configurations, their attributes, and which one is appropriate for a given application.
Hydraulic Flat Tappet
Even though the OEMs abandoned flat tappet hydraulic cams decades ago, it remains the largest segment of the aftermarket cam industry. The hydraulic mechanism provides a means of self-adjustment to the valvetrain, essentially eliminating maintenance in service, and does away with the need for precise valvetrain adjustment. The hydraulic plunger in the lifter body automatically zeroes-out the clearance in the valvetrain, soaking up production tolerances in the engine assembly in the process. The system works so well that most OEM engines are equipped with simple, non-adjustable, valvetrains. The travel of the lifter’s internal plunger provides a wide target for tolerance, and as long as the components are bolted together in that range of travel, a functional, quiet, and reliable valvetrain is the result.
The second major variation in cam types is whether it is a flat tappet or roller follower.
All-out racing performance was never on the agenda when hydraulic lifters were conceived. The very hydraulic mechanism that defines the system can create a source of instability in the valvetrain, putting a cap on rpm and power. This condition will always manifest at higher rpm, potentially curbing the power curve prematurely, representing one of the key shortcomings of hydraulic flat tappet cams. These instability problems can be minimized by careful selection of the rest of the valvetrain components and springs. You will work harder as the targeted rpm range increases, but satisfactory performance is not difficult to achieve in applications under 6,000 rpm. Flat tappets are inherently limited in spring load capacity, with the point of failure being where the lifter meets the lobe, again putting a limit on this type of cam’s ultimate performance potential. In the rpm and lift range of the typical street performance engine, these shortcomings may not present themselves as an issue, making the hydraulic flat tappet a good inexpensive choice for a moderate street application.
These springs with over 500 pounds open load would quickly destroy most flat tappet cams,
Solid Flat Tappet
A solid flat tappet differs from a hydraulic in that there is no internal adjustment mechanism. Clearance for operation, known as “lash,” is set at the valvetrain, allowing the valvetrain to fully unload while the cam is off its lift cycle. A solid flat tappet is the simplest type of lifter arrangement, and this simplicity is the solid flat tappet cam’s greatest asset. It leaves very little to go wrong or cause rpm-limiting instability in the valvetrain.
In terms of rpm and power potential, the solid flat tappet works very well, and cost for the cam and lifters is comparable to a hydraulic flat tappet, though providing for lash requires an adjustable valvetrain, which adds to the cost in many applications. Periodic valve lash maintenance is required, however this aspect is often overstated. A solid flat tappet cam will generate more valvetrain noise than a hydraulic, but for many performance enthusiasts the solid’s mechanical music is considered a plus.