Pedestal mount/ stud mount differences

[hotwheels]

Ford small block rocker systems:
Pdestal mount:
Small-block Ford roller rocker systems come in two basic configurations: pedestal mount and stud mount, although shaft systems are often used in competition applications (we’ll touch on those too). Which type you choose depends largely on the cylinder head you have and the intended use. All have advantages and disadvantages. However, the advantages of each system will outweigh the disadvantages if the rocker is properly suited to the application.
Pedestal-mount roller rockers are what the 5.0 engine came with from the factory, and what many cam manufac-turers offer in roller form as easy valvetrain upgrades. Pedestal-mount rockers, roller or otherwise, fasten to the cylinder head resting on aluminum pedestals that form a base for the rocker arm to rest upon. The pedestals rest in a sheetmetal channel that ties the rockers together in pairs and prevents excessive side-to-side movement of the rocker tip on valve. A long, 5/16-inch cap screw goes through the center of the rocker’s fulcrum, through the pedestal, and into the boss on the cylinder head.
For most street applications, pedestal-mount rocker arms are perfectly adequate. However, when high horsepower and proportionately high valvespring pressures are used, pedestal-mount rockers have their shortcomings--the most important of which is strength (or lack of it). Though the basic rocker layout is the same used in higher-horsepower racing applications, pedestal-mount rockers employ a 5/16-inch cap screw, which has a tendency to deflect and even break in a high-horsepower application. We’re reluctant to state specific numbers here because we know of many racers who have used pedestal-mount rockers well into the 500hp range with a variety of cam/valvespring combos.
The other shortcoming of the pedestal-mount rocker is its lack of adjustability. Factory rockers and some aftermarket replacement roller rockers use shims for adjustment, while other models use pushrod cup adjusters. These, however, are mainly for the purpose of obtaining correct lifter preload during installation.
Suffice it to say that if you have heads designed for pedestal-mount rockers, use them. If you get the chance to run heads that use stud-mounted rockers, do it.

Stud-Mounted:
Stud-mounted systems have been widely used by OEMs and are popular in street-performance applications for two basic reasons--cost and ease of adjustability. Stud-mounted systems use fewer parts and allow correct valvetrain geometry and lifter preload to be adjusted with pushrod length. The rocker is slipped over the stud, and its tip is allowed to rest on the tip of the valve stem. The pushrod side of the rocker can then be raised or lowered until correct valvetrain geometry is achieved, which is typically done through the use of an adjustable pushrod.
For the bulk of street-performance engines and many racing engines, a stud-mounted rocker system is all that will be required.
Shaft-mounted systems are typically used only in maximum-effort racing engines where budget isn’t a consideration. Shaft-mounted systems are more stable than stud-mounted systems.
They also allow exact placement of the rocker tip over the valve tip, because the rocker can be moved from side to side. The same can be done in some stud-mounted applications by machining the pushrod guideplate, but this is difficult and time-consuming. Unlike a stud system, however, correct valvetrain geometry isn’t always easy to obtain. Because the rockers are attached to a shaft--which, in turn, is mounted rigidly to the cylinder head--valvetrain geometry can sometimes be altered only by raising the shaft stands through the use of shims, or lowering them by machining either the stand or the cylinder head. Most stud-mounted cylinder heads can be fitted with a shaft system, but this almost always requires machine work to the cylinder head at additional cost.