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Curved-top tappets

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For those familiar with the design of overhead cam engines, the most common type of cam follower used in bespoke race engines of this type is the solid 'bucket' tappet. These are akin to the flat-faced followers used in pushrod engines, except that the load path is directly from the cam lobe to the lash-cap. They have much to recommend them - they are a geometrically simple part, and lots of people understand how to design and make them. So few people outside Formula One use...

Roller lifters

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In terms of circuit racing, the pushrod engine is most famously used in NASCAR competition; while some other race series allow all kinds of valve actuation, NASCAR mandates cam-in-block and overhead valve engine architecture. One aspect of valvetrain development that affects engine design and development engineers all over the world is valve lift profiles, and there has been a strong tendency over the years to design cam profiles that are more 'aggressive' in terms of using ever...

Bad valve spring wire can ruin a racer's title hopes

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In the Pro Stock Motorcycle category of NHRA Full Throttle Drag Racing Series, there are three engines currently in the game. Only the two-rider Vance & Hines team uses the Harley-Davidson Screamin' Eagle, while the balance of the field is split between the Buell engines, supplied by S&S Racing, and Suzuki engines, furnished by Vance & Hines' workshops. While Harley-Davidson puts a good deal of support behind its factory team, and S&S has managed to get NHRA to open...

Exhaust valve materials

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The poppet valves of a four-stroke engine have an arduous life, and the current design trend of engine downsizing in production vehicles and several race series is likely to make their life more difficult still. With downsizing comes boosting, mainly in the form of turbocharging; any form of boosting leads to increased temperatures and pressures in the combustion chamber, and much higher exhaust gas temperatures. The exhaust valve, which already has much higher temperatures to deal with...

The importance of natural frequencies

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Some of the recent articles concerning pushrod valvetrains have tried to explain the importance of valvetrain stiffness. The advent of the Spintron tester, and its widespread deployment in the r&d shops of engine builders, has given engineers a better insight into valvetrain behaviour, especially the deviation from the 'theoretical' valve lift curve we might expect the lifter/pushrod/rocker to impart to the valve. Anything that doesn't behave as an infinitely stiff member...