1 A stock sled-type rocker...
1 A stock sled-type rocker arm with ball fulcrum is shown here. While you can get stock type replacement rockers made from better materials, they should be considered only for extremely tight budgets and/or the most basic of engine builds. The wide contact pad and gentle radius on the rocker is forgiving of incorrect pushrod lengths, but you're still giving up power via friction and less than accurate geometry, not to mention stock rockers don't always have enough movement to accommodate higher lift aftermarket camshafts.
The typical four-stroke engine is made up of hundreds of parts. These parts are all designed and engineered to work together to make a prescribed amount of power, torque, engine longevity, and other parameters for the engine's design (or more accurately what management has told the engineers it needs to do for a specific cost). As long as these parameters are kept in check, the engine will provide the horsepower, torque, longevity, et al, it was designed for. However, if you begin to make changes to that internal combustion engine, be it a camshaft upgrade, new high-flow cylinder heads, or any number of hard part upgrades, you have effectively changed that engine's engineered design and steps need to be taken to ensure that the new parts are engineered to work with the other new or existing parts of the engine.
One of the internal combustion engines' greatest mysteries centers on its valvetrain components. The inner workings of an overhead-valve engine's valvetrain is often a head scratcher to the most died-in-the-wool car person. You can talk stroker engines, torque converters, or rear gear ratios, but start talking about pushrod length, rocker arm ratios, and spring seat pressures and most of your buddies with automotive knowledge will start looking at their watches and mumbling something about having to go home. Fear not, the mystery behind all those moving parts isn't black magic, but instead is simple math.
When it comes to your engine's rocker arms, their job is to transfer the camshaft's rotational movement into an up and down movement via the rocker arm's pivot point, which in turn opens the engine's valves. The rocker arm's size is expressed in a ratio, as the pivot is not in the center of the rocker (like a see-saw), but instead, offset to one side. For example, the stock small-block Ford rocker arm has a 1.6:1 ratio, and the parts are more commonly referred to as "1.6 rockers." This mechanical advantage means that the rocker arm tip moves 1.6 times the camshaft's lobe lift. For example, let's say your camshaft is a single pattern cam with 0.310-inch of lobe lift. With a 1.6 rocker mounted the cam's lift becomes 0.496-inches of lift (0.310x1.6). This is the typical measurement you see on a cam card or in a catalog with the footnote "with 1.6:1 rocker arm ratio" or sometimes stated as "with stock rocker arm ratio." This is a very effective way to increase valve lift (and duration slightly) without ever touching the camshaft in the engine. For example, the same cam specs, but with a popular aftermarket 1.7:1 ratio rocker arm would be 0.527-inch of lift (0.310x1.7). You've just increased your cam's lift 0.031-inch by simply bolting a different rocker arm on. Comp Cams tells us that the newest cam profiles are more aggressive and designed for the 1.6 rocker ratio, where as older cams and Ford Racing "alphabet" cams work well with the 1.7 rocker. You have to consider though that when you go up in lift, it's harder on the valvespring, it speeds up the cam profile (makes it more aggressive, and can be noisier), and makes the valve come off the seat faster. You also have to pay more attention to piston-to-valve clearance and coil bind.
2 Comp's Magnum rocker arms...
2 Comp's Magnum rocker arms are made from 8620 chromoly steel, will not flex like a stock stamped rocker arm, and will provide more accurate rocker ratios and valve lift. While only employing a roller tip (it still uses a ball type fulcrum), these rockers are a nice upgrade for an engine that has less than 350 lb/in open spring pressure. Best of all, they will fit under most stock valve covers for a nice stealthy upgrade to your engine. Comp Cams offers several styles of steel rockers with full roller bodies as well.
3 Aluminum bodied rocker...
3 Aluminum bodied rocker arms, like these Comp Cams Ultra-Gold ARC series, feature a lighter body than the typical steel roller rocker arm to free up power, and feature both a roller tip and a roller bearing fulcrum. However, aluminum rockers require more room, as they are physically larger than their steel rocker counterparts in order to have the same strength. This can cause fitment issues with head studs, valvesprings, and even the valve cover itself.
4 a. Of course if you're...
4 a. Of course if you're going to run an aftermarket adjustable rocker arm setup, you'll need rocker arm studs and guideplates (as well as hardened pushrods) to make it all work.
4 b. Aftermarket heads usually...
4 b. Aftermarket heads usually have the necessary machining and often come with studs and guideplates. However, if your new heads do not come with attaching parts, or you are having other heads machined to accept rocker arm studs and guideplates, you'll have to purchase the right parts. Rocker arm studs are available in 3/8- and 7/16-inch sizes, so be sure to purchase the right ones for the rocker arms you are using.
5 a. For serious rpm use,...
5 a. For serious rpm use, you have a couple of options. You can use a stud girdle or you can convert to shaft mounted rockers. They both improve the stability of the valvetrain by tying the rocker arms together. The stud girdle uses special rocker arm adjusting nuts that the girdle slips over and is then secured to.
5 b. Shaft mount rocker systems...
5 b. Shaft mount rocker systems place the rockers either on a common shaft (such as the FE big-block system shown here), or ties each pair of rockers to a smaller common shaft. Again, this increases the stability and accuracy of the valvetrain's motions.
6 Pushrods come in many flavors,...
6 Pushrods come in many flavors, but for the most part you'll find the typical steel tube in 5/16-inch diameter with welded pivot ball ends, as these examples are seen here. They work fine for a stock engine, but like their sled rocker arm counterparts, are not the most accurate. They can flex enough with aftermarket springs/high lift cams to reduce the amount of true lift the valve sees. Plus they are not hardened to work with pushrod guideplates (the pushrod actually rubs/touches these plates to keep them in line with the valve it actuates). Finally, we've actually seen the pivot balls fail at the weld with aggressive cam profiles.
7 A hardened one-piece pushrod...
7 A hardened one-piece pushrod is your best bet when you upgrade to an adjustable valvetrain/rocker arms. The Magnum and Hi-Tech pushrods from Comp Cams feature 0.080-inch seamless wall chrome-moly tubing with formed ends, heat treated and finished in a black-oxide coating with laser-etched part number and length on the body. You have less deflection with one-piece pushrods due to their thicker walls and better materials. One-piece pushrods are more exacting with higher production tolerances. You can make more power with a better pushrod, as at higher rpm, you get less lift with a deflecting pushrod. The Comp Cams staff we spoke with suggested putting the best pushrod you can in your build. They have seen 10-15 rwhp with the use of a stronger pushrod.
8 a. As we stated earlier,...
8 a. As we stated earlier, ordering a cam kit with matched springs, or fully assembled aftermarket heads is your best bet to ensure your valvespring pressures, installed, height, and other measurements are within spec out of the box.