5.0 Mustang & Super FordsHow To Engine
Shaft-Mount Rocker Arms - Solid...And They Rock
Boosting Our 5.0's Rev Confidence With Crane's New Pro-Series Shaft-Mount Rocker Arms
Horse Sense: Although we're using our Project Real Street '89 LX coupe as the subject of this test, please understand that use of shaft-mount rocker arms is strictly prohibited in our 5.0 Mustang & Super Fords Real Street class. While it doesn't happen often, we always chuckle when Editor Turner shows us his wild side-which sometimes has him marching to the beat of an unconventional drum-and makes decisions such as using the class' flagship 'Stang for non-rules-compliant tech efforts. In all seriousness, the irony is a matter of convenience. March on, Turner, march on.
The 5.0 small-block has long been this magazine's engine of choice for street/strip/road-race Mustangs. Don't get us wrong-modular power is where it's at today, but there's something special about strong pushrod bullets.
There have been more than a few articles published that explain in detail the purpose and function of a four-stroke, internal-combustion engine's valvetrain components-from camshafts to pushrods in 5.0 and 351W engines, as well as lifters, springs, rocker arms, and such.
When we discuss a specific 5.0 valvetrain piece, our main intent is to give readers information about the installation, functionality, and overall influence of the part on the engine's performance. An example of this is Uncle Robin Lawrence's study of an NMRA Real Street engine's valvetrain as it was being evaluated under the high-rev influence of a SpinTron.
Robin's report ("Spin Control," Aug. '06, p. 150) focuses on using a SpinTron to track all the deep, internal goings-on in an engine's valvetrain during cam-lobe cycles. Based on data, changes are made to determine the best combination of pushrods and springs, which controls the havoc that breaks loose at high rpm.
A camshaft lobe triggers the up/down movement of the rockers by way of lifters and pushrods, and thus controls the opening and closing of valves. When a cam lobe raises the outside/butt of a rocker, the inside/tip is pressed against the valve stem, opening the valve. Conversely, when the cam's rotation lowers the butt side of the arm, a rocker's tip lifts and allows the valvespring to close the valve.
Rocker arms play a major role in camshaft/ pushrod/valvespring harmony. In the case of stud-mount roller rockers common to supercharged and nitrous-injected Real Street bullets and pushrod engines, the arms act on a needle-bearing-and-trunnion-style pivot in the center of their housings.
Our '89 Real Street LX notchback is motivated by a D.S.S.-built 306 short-block, stuffed with flat-top pistons and topped with Trick Flow's veritable Twisted Wedge cylinder heads. Per class rules, our bullet's camshaft is OEM stock, so D.S.S. took extra care to pay close attention to piston-to-valve clearance. We went with 1.7 rockers with 7/16 studs, as opposed to factory-spec 1.6 arms, in order to achieve as much total valve lift as possible. Note that rocker-arm ratio represents the number of times a rocker arm moves a valve in relation to the total advertised amount of cam-lobe lift. When multiplying the rocker ratio by cam-lift specs, we're able to determine the total amount an intake or exhaust valve moves from its seat during a cam cycle.
A rocker-ratio upgrade (1.6 to 1.7) is one of the oldest valvetrain-related tricks in the book of Mustang performance, as is installing stud-mount rocker arms as replacements for pedestal-mount pieces. The latter modification is done in the name of strength and stability. Rocker arms move at a blindingly quick rate when the engine's rpm is high; maintaining tip contact with pushrods and valve stems with minimal friction and deflection is critical to their efficiency. Deflection is the degree to which the rockers are displaced at high rpm.
Theoretically, because of their design, pivot-ball-style, stud-mount rockers aren't as efficient at reducing friction as rocker arms that utilize the needle-bearing-and-trunnion setup as their pivot source, mainly because the balls have a greater tendency to move around (deflect) as rpm increases. The needle-bearing-and-trunnion centers are dramatically better. The best method for knocking out excessive deflection is by installing shaft-mount rocker arms.
We selected the Pro-Series shaft mounts for this project. Its rocker bodies are made of 2024 billet aluminum. They're shot-peened for extra strength, and each stand is machined from billet steel or heat-treated aluminum stock for strength and durability. Crane's Tony Vigo tells us that for drag racing, the offset arms we're using will stand up to a SpinTron-tested minimum 800 pounds of open-spring pressure, which is light years beyond anything we'll experience with Real Street's engine. We're using 0.345 intake/ 0.265 exhaust offsets to ensure the rockers' tips will remain centered over the valve stems during opening/closing. We should be in great shape if we turn up the wick on our project car.
Our former tech editor, Mark Houlahan, stepped in to bolt on the new rocker system. Although our Twisted Wedge heads used studs initially, the new shaft-mount system is designed to bolt directly onto the heads. There's no need to modify or remove them from the engine to install the rocker arms.
We feel compelled to reiterate the message to NMRA Real Street racers that Crane's Pro-Series, shaft-mount rocker arms aren't legal for the class, so don't get any crazy ideas about trying to bend the rules. You never know when you'll be asked to remove a valve cover so tech officials can take a closer look at your rocker arms. If you want to run a Real Street-style combo in your street/strip 'Stang, anything goes.
Crane's new Quick Lift rocker-body design provides an initial valve-opening rate at least 0.100 inch higher than the advertised ratio. It then decreases through the first 0.300 inch of net valve lift until the advertised ratio is achieved. It's maintained until the valve is within 0.300 inch of the seat, where the ratio then goes back to 0.100 inch more than advertised.
This varying ratio is a result of the pushrod seats' location in the bottom of the rocker bodies. Quick Lift aluminum bodies have a lower pushrod-seat location compared to other rocker-arm bodies, causing pushrod tips to contact the rocker bodies at lower points in the pushrod seats' operating arc.
This change in effective rocker-arm ratio has been proven to produce horsepower and enhance throttle response.
Intake/exhaust rocker-arm tandems are mounted on 5/8-inch shafts. The rockers' retaining snap ring is placed in a groove machined into the middle of the shaft, and thrust washers are placed on both sides of each arm (0.015-inch/intake and 0.031-inch/exhaust). Make sure you have four individual thrust washers before installing them; they have a tendency to stick together and give the impression there are fewer than four. Don't be stingy with the assembly lube during this process. Mark uses an Allen wrench to fully seat the pushrod-adjustment set screw, and then backs it out one full turn. This ensures that the internal oil passages in the adjusters align with the rockers' oil passages, eliminating any chance of binding the pushrods when the rockers are installed.
Each shaft is mounted to its stand using 1.25-inch, 5/16 Allen-head bolts on the outside, to the right and left of the intake and exhaust rockers, respectively. A shorter 5/16 bolt (1.00-inch) goes in the area between both rocker arms.
The long and short shaft bolts are torqued to 28 lb-ft.
Mark confirms we have correct intake and exhaust-pushrod length by preloading the lifters. This process is no different than the way it's done with stud-mount roller rockers. Here, he uses the wiggle technique on the rocker arm while turning the pushrod-adjustment set screw. When proper setting is achieved for each of them, 7/16 adjustment-screw jam nuts are torqued to 24 lb-ft.
The blinging brightness comes from the Mikronite finishing process that each Pro-Series rocker arm undergoes for strength and smoothness. The Mikronite improves durability and impact resistance on each rocker arm while reducing friction, resistance, and corrosion. With Robin's SpinTron data as our confirmation for now-Real Street's engine wasn't in dyno-test condition when the swap was performed-we're sure the new Pro-Series shaft-mount rockers will do a better job of keeping our valves under control as rpm increases. With the Quick-Lift geometry in Crane's new arms (see sidebar), we wouldn't bet against Real Street's 306 gaining a few additional horsepower.
We experienced a clearance problem with the OEM valve covers, as well as several others we thought might work. This is the pile of failed attempts.
Our friend Mark Lambacher turned us on to this set of Trick Flow's tall covers (PN TFS-51400802; $122.95). They fit without any clearance issues. Trick Flow's 1-inch intake spacer kit is required for clearance between the covers and our Track Heat intake manifold; an optional oil fill/breather tube is available for the Trick Flow covers. Drilling a 1 1/4-inch hole in the passenger-side cover is necessary for installing any breather system.