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Pushrod Properties

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When engaged in building Dodge Mopar engines for use in USAC’s National Midget series, Bob Wirth of Hayward, California relies on pushrods from Smith Bros of Bend, Oregon. He works with the raised port (RP) head and relates, “The RP cylinder head layout is really hard on parts. The intake rocker is offset 3/4-inch and that exacerbates the stress at the adjuster and at the end of the pushrod, because you’ve got a rocking couple across the span of the rocker. This ‘ball...

Valve Spring Challenges

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There are valvetrain tricks to making good power and obtaining durability and longevity from a Dodge Mopar USAC National Midget engine, according to engine builder Bob Wirth of Hayward, California. “We need them all.” The biggest problem with midget racing – like Pro Stock drag racing – is that the rate of acceleration of the engine can be exceptionally high, above 2000-3000 rpm per second. The valve spring must be able to control the mass of the valvetrain through...

Poppet Valve Materials

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Last month, we looked at the application of hollow valves, and noted, as had Anne Proffit’s recent article, that titanium is a popular choice for these components. Many engineers who specify hollow valves do so for reasons of mass reduction and improved valve control; hence titanium is a natural choice in this respect.Titanium has very low density compared to the more traditional poppet-valve materials and so is the kind of material that we look to when trying to minimise mass as part...