Rocker Arm Tech With Comp Cams and T&D Machine - Off Your Rocker
From the November, 2012 issue of Chevy High Performance
By Jake Amatisto
Photography by Courtesy of the Manufacturers, Jake Amatisto
The rocker arm is possibly the third most abused part in your engine. The connecting rods take the cake for the most abuse, followed closely by the piston assembly, but we like to think the rocker arms get the bronze for beatings when you’re goosing the throttle in your V-8 of choice.
When it comes to building a performance engine, rockers can do more than simply transfer the motion of the pushrod; rocker arms can change rpm limits, rpm acceleration, and they can even alter your camshaft’s overall behavior. Although simple in theory, rockers are actually far from simple in the high-performance and racing world. In a stock engine, we imagine the rockers live a boring life; basically just transitioning the movement of the pushrod, easily pushing down the low-pressure single coil valvesprings until the cows come home. But as your desire for horsepower increases, the durability and construction of the rockers you choose has to improve as well if you want the most from your engine combo.
Choosing the right rocker isn’t the only thing to keep in mind, you also have to install them correctly, and sometimes, if you don’t know what to look for, it can be tricky. As we change camshaft profiles, valvespring heights, and mill and deck our engine blocks and heads, those all factor into getting the rockers to fit properly and valvetrain fitment is crucial for a long-lasting engine combination.
T&D Machine is one company that prides themselves on creating some of the most radical rocker arm systems, including rockers for Pro Mod drag racers and NASCAR “Cup” engines. When you’re limited to specific cam profiles, engine builders often use custom rocker ratios to achieve their desired lift without physically changing the cam specs. However, high-ratio rockers increase the velocity of the valve, which can decrease the life of valveguides and they can also complicate getting the geometry correct.
According to COMP Cams, there are three ways to improve your engine’s power output through a rocker arm change: Use a higher ratio rocker arm to increase overall cam lift and duration, make the rocker body stiffer so no lift is lost by flex, or lower the weight of the rocker so it can accelerate quicker. Increasing the rocker ratio is a way to trick your camshaft into thinking it’s bigger than it actually is. By manufacturing rocker bodies with various arm lengths, this increases the ratio, thus increasing the final lift and duration at the valve. This is oftentimes what gearheads do if they need more cam but don’t want to pull the engine apart. As valvespring pressures increase, rocker body stiffness plays a huge factor in getting the most from your rockers. For years, the engines in the NASCAR circuit used aluminum rockers, but relatively recently engineers have figured out that the amount of flex coming from pushing on super-stout valvesprings was reducing the overall lift of their camshaft, which prompted all the NASCAR teams to switch to lightweight, yet low deflection rockers so they could get every fraction of cam lift from their profile. Reduced rocker body mass is another way companies have improved rocker arm performance over the years. The more rpm your engine experiences, the more valvetrain mass becomes important. For a low-rpm engine, rocker weight/mass is not crucial, but on an 8,000- to 10,000-rpm screamer where the rockers move incredibly quickly, every gram counts.
Read on as we explore how to properly install COMP’s Ultra Pro Magnum stud mount roller rockers as well as give some inside info from COMP Cams and T&D Machine’s engineering department.
You only need a handful of...
You only need a handful of key items to ensure your engine will have correct rocker arm geometry; light “checker” springs, a retainer and lock, a rocker, a dry-erase marker, and an adjustable pushrod. By checking your pushrods for the correct length you get better engine performance by achieving the absolute most valve lift, while preventing excessive valveguide wear that comes from a misaligned rocker.
COMP Cams offers an adjustable...
COMP Cams offers an adjustable pushrod design that allows you to measure without needing giant calipers.
This design allows the builder...
This design allows the builder to determine the ideal size by counting the number of turns it takes to get the rocker tip in the center of the valve stem. Each rotation represents 0.050 inch.
With the tip of the valve...
With the tip of the valve stem coated with some ink and the adjustable pushrod fully collapsed, install the rocker without the posi-lock and unscrew the tip until you find the ideal alignment. Sometimes if you have the wrong adjustable pushrod, no amount of unscrewing will get the rocker in the right place, so an Internet search may get you in the ballpark. Or, if you have your stock pushrods you can measure those to see which adjustable one you will need. Keep in mind, head and block milling, aftermarket cylinder heads, and various length valves are all factors that affect pushrod length and in turn, overall valvetrain geometry so it’s important to get this right.
Here’s a perfect example of...
Here’s a perfect example of what you don’t want to see after bolting on your valvetrain; the roller way above the valve stem centerline. If you run your engine with the tip off-center like this, it side-loads the valve, which can cause issues with valveguides and can unevenly wear out the tip or the valve.
Once you lengthen the pushrod...
Once you lengthen the pushrod and get the roller tip in the center, bolt down the rocker body and rotate the engine a few times. Remove the rocker and observe the valve tip; you’re looking for the narrowest, most center-aligned sweep. If it’s too far to one side or too wide, you’ll need to recheck it. According to a few engine builders we spoke with, typically the sweep will be less than 0.100, but that number can vary depending on engine type and rocker style.