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Roller Rocker Arms - Rockin' Out
We Add 10 RWHP And 16 Lb-Ft Of Torque By Simply Swapping Rocker Arms.
There is no doubt that you can make huge power with pushrod 5.0L engines. Over the years, engine builders have figured out countless tricks for making horsepower. Even though some remain a secret, its common knowledge that there is power to be had by installing a larger camshaft or better valvetrain components.
But what happens if you installed a camshaft in the early phases of your build and have since added parts, like a larger intake manifold or different exhaust? If that is the case, you may benefit from a bigger camshaft. Iif time and budget are of no concern, you could install a larger camshaft and be done with it. But what if your budget doesn't allow for that? Well, we may have the answer.
Roller rocker arms are a key component in the 5.0L's valvetrain. The camshaft pushes up on the lifters, which moves the pushrods. The pushrods transfer energy to the rocker arms, which rock on a fulcrum to physically open and close the intake and exhaust valves. A rocker arm is simply a lever designed with different ratios to open the valves further off the seat and at different rates than the camshaft's actual lift and duration. By changing the ratio of the rocker arm, you can achieve the effect of a larger camshaft without having to disassemble the engine to swap bumpsticks.
MM&FF Associate Editor Marc Christ is the proud owner of the two-tone SSP coupe that has graced the pages of MM&FF over the past year. The LX started as a high-14-second street Stang that was a little more show than go. We've added aftermarket heads, a larger intake manifold, and a nitrous oxide kit, to name a few.
Throughout all of these performance upgrades, the no-name camshaft has remained constant. It checks in at 0.498/0.498-inch lift with 220 degrees of duration at 0.050-inch lift (identical to FRPP's "E" cam). We think there is performance to be gained with a little more cam.
When we installed the Edelbrock E-Street aluminum heads, they came with aluminum 1.6 roller rocker arms. In an attempt to gain a few extra ponies, we decided to swap the Edelbrock 1.6s for a set of 1.72s from Summit Racing. The Summit rocker arms (PN SUM-G6942B) are affordably priced at $229.95 and can be installed by most backyard mechanics in a few hours.
(Editors Note: When swapping rocker arms, take into account possible piston-to-valve clearance issues. Increasing duration via rocker-arm ratio may require valve reliefs to be cut into the pistons. Stock 5.0 engines with stock valve sizes can safely use 220-222 degrees of duration depending on lobe centers, but more can make for potential contact.)
"Rocker arms are nothing more than a lever," explains Ron Robart of Fox Lake Performance Products. "Increasing the ratio of that lever will increase valve lift and duration by a degree or two. Using stock pistons with 1.94-inch valves usually means you can get away with about 220 to 222 degrees duration if the camshaft is cut on a 112 or 114 lobe center."
To get the new lift specs for our camshaft, we did some simple math. Starting with the known lift with a 1.6 rocker (0.498), we divided by 1.6. This gave us 0.311, which is the actual lobe lift of the camshaft. We then multiplied that by 1.72 (the ratio of our new rockers) to find the new lift measurement, which is 0.535 inch.
Before starting, we tested the LX on our Dynojet. With the 1.6 ratio rocker arms, it spun the rollers to 274 rwhp and 277 lb-ft or torque. After the rockers were swapped and adjusted, we strapped our coupe back on our Dynojet and it laid down 284 rwhp and 293 lb-ft of torque, for a gain of 10 hp and 16 lb-ft of torque. Not bad for a few hours in the shop!