jgKRI... OK... but not necessarily agree.
On-line article from enginebuildermag.com.... "Selecting The Right High Performance Rocker Arms"
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As for rocker materials, Elliott offers the following observations:
Stamped steel rockers should only be used on engines with less than .600? of valve lift and at engine speeds below 6,500 rpm. Higher lifts or engine speeds require upgrading to some type of performance rocker (aluminum or steel).
Aluminum rockers are lightweight, easy to manufacture, and have a dampening effect on the valvetrain. The downside is their mortality rate, since all aluminum rockers have a cycle life.
The pros of using steel rockers are that they are more durable (extended cycle life), and stiffer with a slight deflection improvement over aluminum. The downside with steel rockers is that they are not as easy to manufacture, they can be heavier and harder on other valvetrain parts.
The lighter the rocker, the less mass the valve spring and pushrod have to accelerate, stop and accelerate in the opposite direction. But each application dictates how light of a rocker can be used. Removing weight from the roller tip always pays the biggest dividends, as long as the rocker is capable of handling the loads for that application.
Yella Terra
Roger Vinci at Yella Terra High Performance Engine Parts agrees with the other rocker suppliers that more and more racers are choosing steel rocker arms and shaft systems for high rpm applications. “Keeping the valvetrain as stiff as possible while maintaining the lightest weight over the nose of the rocker is our goal. We have one of the smallest nose wheels in the industry. The lightweight technology in our Ultralite LS rocker designs allows the use of lighter spring weights.”
Vinci says strength is of utmost importance in a rocker arm (far more important than its appearance or packaging!). “We use a 2024 T3500 [2024-T3510 or -T3511?] alloy in all of our higher end rockers. Some manufacturers start with an inferior alloy and anodize it to make it look good. But anodizing an alloy can reduce its strength up to 50%. That’s why we do not anodize our rocker arms.”
Vinci says creating as much lift as possible via the rocker arms is paramount to stabilizing the valvetrain. “We know that utilizing the leverage of the rocker shortens lifter travel, which lowers friction. It also lowers lifter and pushrod inertia and can greatly increase the rate of lift of the valve as comes off the seat to initiate and sustain airflow. This can allow the engine builder to use lighter pressure valve springs, which we believe is always more favorable when possible.”
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NOTE. 2024 cannot/should-not be die-forged, so plate or bar or extruded shapes are necessary raw stock. 2219 is a suitable die forging alloy ... IF You want mass production [precision] die forgings generally produce the optimum grain-flow for durability, strength and relative ease of manufacturing. I agree: try to avoid anodic coatings due to early crack initiation. Post machining/NDI shot peening will usually help fatigue life [retard crack initiation] dramatically.
Regards, Wil Taylor
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