| FLAT TAPPET vs. ROLLER TAPPET LIFTERS
In nearly all circumstances, a good roller camshaft design will outperform its flat tappet counterpart. Among the benefits of roller cams are higher tappet velocity, more lift and more area, along with reduced valve train friction (often a 20+ HP increase) and higher engine RPM with little effect on low speed drivability and power.
Roller tappets are also reusable, which makes it possible to swap just the camshaft without the expense of new lifters. And finally, roller tappets are far less prone to wear – allowing higher spring loads – and they are more consistent with today’s oils.
The biggest advantage with a flat tappet cam and lifters is the up front cost. It can be significantly less expensive to use a flat tappet setup but should you decide to install a new camshaft, you will need new lifters as well.
HYDRAULIC vs. MECHANICAL (SOLID) LIFTERS
Both lifter types look the same from the outside, with both having pushrod seats held in by a retaining clip. In a hydraulic lifter the seat moves by means of a hydraulic valve and oil pressure within the lifter. The mechanical lifter does not have a valve and is solid.
The pushrod seat in a solid lifter sits upon an internal step inside the lifter body, preventing it from moving. The hydraulic lifter, on the other hand, has a pushrod seat that sits on top of a moveable hydraulic mechanism which acts like a tiny hydraulic pump. Below this mechanism are a valve and spring that produce an upward force, moving the seat up against the pushrod when the lifter is on the base circle.
Solid cam designs require a running clearance or “valve lash.” Hydraulic cams are the exact opposite. In a standard hydraulic lifter the pushrod takes up all of the clearance and submerges into the lifter’s pushrod seat approximately .020"-.070". The distance that the pushrod submerges is known as the “pre-load.”