In this article we will go over some of the main differences between pedestal rockers and stud mount. This will highlight some of the advantages and disadvantages between the two of these options.
The pedestal mount rockers are what your factory Fox head would have equipped form Ford. On these styles of rocker arms you will have a main pivot point that is bolted directly to the cylinder head. Overall setup on these can be a tad more difficult in some cases. Using aftermarket camshafts and roller rockers can require shims between the rocker and the cylinder head to properly achieve zero lash. These are perfectly fine for stock or mild upgrades overall. This “bolt-in” design can be a little weaker overall, so you will need to consider this when doing substantial performance upgrades on your engine. Stock heads can be upgraded from the pedestal mounts to the more popular stud conversions.
The stud mount rocker assemblies replace the bolt in pedestals with a stronger stud configuration. Stud mount will allow a wider range of adjustments without the use of any shims. Lash is achieved through the use of a poly lock style nut. Overall valve train geometry is easier to achieve with these setups. When using aftermarket camshafts with larger lifts, you want this range of adjustments these styles offer. Most aftermarket cylinder heads like SVE, Trickflow, and AFR use these type of rockers because of the added strength and the added benefits we have discussed.
Not all of these kits I have mentioned may be best suited for you, but remember we are always a phone call or an email away. Our staff is well versed in this subject as well as all of the 79-19 Mustangs! As always check out our comprehensive articles, videos and website at LMR.com.
When installing pedestal mount rockers, make sure you properly lube the rockers, attaching hardware and also make sure the flat side of the rocker trunion is facing up. First step is to make sure the cylinder you are working on has the cam lobes positioned so that both valves are in the closed position. Next, make sure the push rods are seated in the cups and tighten up the mounting bolts by hand until they are snug. When they are snug, you should still be able to spin the pushrod, but not have any up and down end play. Torque the mounting bolt to 15 ft/lb (or recommended manufacturer torque spec for aftermarket rockers). After the rockers are torqued, you should still be able to spin the pushrod. If you are not able to spin the pushrod, shims are needed for additional clearance. If your pushrods are too short and have excessive end play, you need to measure for longer pushrods.
Installing stud mount rockers is similar to pedestal mount installation. Make sure the flat side of the rocker trunion is facing up and slide the rocker assembly down over the stud. Lube the stud and install the retaining nut onto the threads making sure the allen head lock screw is backed out. With the cylinder you are working on at top dead center (TDC) or where the camshaft would have both valve in the closed position, tighten the retaining nut by hand until there is zero lash. You should be able to spin the pushrod freely with no up and down endplay movement. Once you have achieved zero lash, turn the retaining nut an additional quarter to half a turn to set the pre-load on the lifter. As soon as you set pre-load, screw down the allen headed lock to set it in place and prevent the retaining nut from moving.
Now that the 2 most common styles of rockers have been established, lets move on to rocker arm ratio. Rocker Arm Ratio is the length of the valve side of the rocker arm to the center (or pivot point) of the rocker arm divided by the length of the Cam or Pushrod side to the center of the rocker arm. Typically the valve side is longer than the pushrod or cam side, so the rocker arm will "multiply" its motion by its Rocker Ratio. This ratio is typically in the range of 1.6 to 1.7, meaning that for each .100" of pushrod or cam motion you would get .160" to .170" of valve motion. Changing the rocker arm ratio on your engine will have a direct effect on your camshaft lift specifications. The higher the ratio rocker you use, the more valve lift you will see. For instance the Ford Racing “E” cam part number M-6250-E303 is based off of a 1.6 roller rocker and has a lift of .498”. If you change your rockers to a 1.7 roller rocker arm, it will change that lift to .529” just by swapping rocker arms. This is an easy way to modify your cam specs, but must be used with caution. You can’t just blindly throw larger ratio rockers on your current set up to achieve more lift. You have to make sure that the rest of your set up (springs, retainers, valve-train geometry etc.) will function properly with this change.