Types of Camshafts:
Flat Tappet Vs. Roller
The lobes between flat tappet and hydraulic cams look very different even if the specs are
The main difference between flat tappet and roller cam types is how they interact with the lifter. A flat tappet is so named because the lifter surface appears to be a flat plane. It’s actually very slightly convex (and the cam lobe is ground with a corresponding taper), which helps it rotate as the cam lobe slides across it. Failure of the lifter to rotate would actually result in very accelerated cam and lifter wear that would eventually cause failure. Roller cams, on the hand, look like a tiny caster. The wheel rolls across the cam lobe so spinning is not required to reduce wear. Moreover, roller lifters are always keyed in place by the lifter bore or through link bars that attach one to another.
While there are obvious wear benefits to a roller versus a flat tappet, there are performance gains to be had as well. From a practical standpoint, flat tappets are limited mostly by spring load and rpm. They are still used by many successful racers, but the trade-off is in longevity of the parts. With conservative valvesprings, flat tappets can last many miles, but aggressive profiles and high rpm require much heavier springs and the pressure increases wear dramatically. There is definitely a point at which it is too great for real-world hot rodding applications. Rollers, on the other hand, can tolerate much higher spring loads and rpm thanks to the wheel and the different geometry of the cam lobe. Essentially, you can spin harder with higher lift and duration for longer with a roller cam. That geometry and greater control tends to tame an aggressive cam relative to a comparable flat tappet. Another practical benefit to a roller cam is that is does not require the traditional break-in that a flat does, which eliminates one possible source of early engine failure. The break-in is extremely critical for flat-tappet engines and must be performed properly to ensure a good lifespan. Don’t ever skimp on the lifters either, always go with a reputable brand of flat tappet lifter to ensure its surfaces are sufficiently hard to survive the pressures.
So are there any benefits to flat tappet cams? Yes. First and foremost is cost. Flat tappets are always the cheaper route due to their inherently less complex manufacturing. Flat tappets also offer the opportunity for increased ramp speed on the cam lobe (how fast the valve opening event begins to happen) because the surface area of a flat tappet lifter is greater, which can be beneficial in some applications.
Hydraulic Vs. Solid
For either flat tappet or roller, hydraulic or solid, it’s critical to make sure the valve
From a hot rodder’s perspective, the key trade-off between a hydraulic and solid cam will be rpm and valve lift potential versus increased maintenance and wear. The key difference between these two types of cams is mostly in the lifter design. Hydraulic cams, whether flat tappet or roller, use a lifter that feature an internal mechanism that continuously adjusts to maintain zero valve lash. That’s ideal for creating a very quiet, maintenance-free valvetrain, which is why they are far and away the most common style of lifter found in any street engine from vintage muscle car to new sedan. That very same mechanism is also the limiting factor when rpm begins to exceed 6,500 rpm (or the cam profile becomes extremely aggressive with high lift or velocity); it can lead to instability in the valvetrain and valve float because the hydraulic internals can actually begin to compress when overstressed.
Solid cams use a lifter than has no such internal adjustment, which gives them an extremely precise transfer of the cam profile to the valvetrain. Their tolerance for high rpm and aggressive profiles means you’ll see them almost exclusively in racing circles and applications where high power and performance are the primary goals. As with hydraulic flat tappets, solid flat tappets are limited in how much spring pressure they handle without severely accelerated wear, but they do have a higher rpm potential. Solid rollers offer the increased spring load capacity of their hydraulic counterparts while offering 7,000-plus rpm stability with ease. The big trade-off with both types of solid lifter cams is that periodic valve lash maintenance is required to keep it within spec, or engine damage can occur. That same direct transfer of the cam profile without any damping also results in increased valvetrain wear, so longevity of parts is diminished versus a hydraulic. Both points are definitely something to keep in mind if you plan on dropping the engine in a daily driver.
One last point to note is that solid and hydraulic cam specs on a cam card are not directly comparable. That’s because the standards are measured at different points on the lobe. For example, COMP Cams’ advertised ratings are usually checked at .008 on a hydraulic, but at .020 on a solid. Even the industry standard .050 measurement isn’t a direct comparison since the requisite lash of the solid roller must be taken into account. That means that a solid and hydraulic cam could have the same duration numbers listed at .050, but the solid cam would actually deliver slightly less effective duration because of the lash ramp and would need to be increased slightly to deliver the same duration at the valve.
The shape of a flat tappet cam versus a roller can be misleading as well. The wheel of a roller cam interacts in a 1:1 relationship to the cam lobe following it exactly while the cam lobe slides across the entire surface of a flat tappet lifter. Essentially, a roller cam requires a physically larger lobe to create the same valve opening and closing events as a similarly spec’d flat tappet. This fundamental difference favors the roller cam as rpm and spring pressure increases.
“Solid cams use a lifter than has no such internal adjustment, which gives them an extremely precise transfer of the cam profile to the valvetrain.”