Camshafts

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Page created by MRHZV8 Jan 26th 2005:

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Aftermarket Holden V8 Camshaft. Click to Enlargen. Photo by

Camshafts:

you can see the lobes on the camshaft opening and closing the valves, altering the size and duration of the lobes determines the "profile" of the cam shaft. Click to Enlargen. Photo by

Lobes are Key:


The key parts of any camshaft are the lobes. As the camshaft spins, the lobes open and close the intake and exhaust valves in time with the motion of the piston. It turns out that there is a direct relationship between the shape of the cam lobes and the way the engine performs in different speed ranges.

To understand why this is the case, imagine that we are running an engine extremely slowly -- at just 10 or 20 revolutions per minute (RPM) -- so that it takes the piston a couple of seconds to complete a cycle. It would be impossible to actually run a normal engine this slowly, but let's imagine that we could. At this slow speed, we would want cam lobes shaped so that:

*Just as the piston starts moving downward in the intake stroke (called top dead center, or TDC), the intake valve would open. The intake valve would close right as the piston bottoms out.

*The exhaust valve would open right as the piston bottoms out (called bottom dead center, or BDC) at the end of the combustion stroke, and would close as the piston completes the exhaust stroke.

This setup would work really well for the engine as long as it ran at this very slow speed. But what happens if you increase the RPM? Let's find out.

Cam from an EFI VK 3.3 Engine showing the GM7 identification. Click to Enlargen. Photo by LEFTS.
GM7 Cam from an EFI VK 3.3 Engine Engine showing the un-needed mechanical Fuel Pump cam lobe. Click to Enlargen. Photo by LEFTS.

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How camshafts Work

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