Automotive Dictionary: Camshaft

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Automotive Dictionary: Camshaft


Throughout this site we use many technical terms, and given the breadth of readership our site enjoys, sometimes we are remiss and incorrectly assume everyone knows what we are referring to. For those that do not, here are some explanations of the technical terms use.
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Camshaft


Camshaft
A revolving shaft on which is set a series of cams designed to operate various mechanical movements such as the operation of the inlet and exhaust valves of a car engine. Driven off the crankshaft, the camshaft consists of a series of machined eccentric lobes that open and close the valves, thus controlling gas flow in and out of the cylinder head. Camshafts have the job of opening the valves and allowing the fuel/air mixture in, and then opening another set of valves to allow the burnt gases out. Different camshafts open the valves for different periods of time (duration), and push the valves open a certain distance (lift). The standard camshaft fitted to most of today's cars is a compromise. Manufacturers fit cams which give a reasonable rev range without sacrificing too much torque, and vice versa.

What you want your car to do will determine the type of camshaft you fit. For a car that will be used for track work, a full race cam would be the best bet. This would allow the engine to breathe deeply at the top end of the rev range, but would sacrifice bottom end grunt to the extent that the car would probably need a big serve of revs to get it moving. A car that was to be used towing heavy loads would be better fitted with a completely different camshaft. That car would need a relatively low profile cam which would give masses of torque at low engine speeds needed to get a load moving and keep it moving up hills.

You can specify either a billet camshaft and have it ground to your own specifications, or have the camshaft already in your car reground for a better profile. In either case, specialist help will be needed to determine the correct duration and lift. Simply returning the camshaft to its standard specifications in older cars can sometimes provide a performance boost. Cams, like any other engine components, are subject to wear. The wearing process can gradually grind down the lobes, allowing the valves to stay closed more than they should. Holden's 308 V8 engines are notorious for such wear, which occurs when the hardening agent on the lobe surface breaks down.
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