When you consider the workings of the internal combustion engine, it'struly remarkable that it works as well as it does considering its crudeinternal demeanor. We can huff cubic inches of air into cylinder boresand combustion chambers, and marvel at the display of power when thebutterflies are pinned. From a distance, it all looks so easy. Butmaking real power takes a whole lot of knowing what you're doing.
You can fit it with a larger carburetor or fatter fuel injectors. Andyou can top off the block with a pair of deep-breathing cylinder heads.But, if you can't get valve timing and function down to a pleasantmelody that allows the fuel system and cylinder heads to sing in perfectharmony, you might as well funnel your working capital into the vitreouschina fixture with the American Standard nameplate [that's a toilet formost of us--Jeff].
The camshaft is your engine's frontal lobe, so to speak. It determinesyour engine's personality more than any other single element. It sits inthe middle of your V-8's valley between the cylinder banks in anoverhead valve design, or above the cylinder heads in an overhead camdesign. In either case, the camshaft's job is a busy one, and that is toproperly time valve-operating events, which allow air and fuel to enterthe combustion chambers, and hot exhaust gasses to leave when theextraction of power is over. And it gets to do this again and again at awide variety of engine speeds. The greatest challenge for us asperformance enthusiasts is to choose a camshaft that allows us to makethe most of our engine package.
I'll Take A V-8!
For the sake of simplicity, we'll focus on the overhead-valve V-8 enginehere. The camshaft has 16 lobes, which open and close 16 valves in atimed sequence with crankshaft and piston motion events. These lobesmove lifters, which are positioned in the block and tied to pushrods,then rocker arms in the cylinder heads, which operate the 16 valves.Rocker arms use leverage to open the valves. As the cam lobe comesaround to its high side and pushes the lifter upward, the pushrod movesupward against the rocker arm. The rocker arm pivots on a shaft or stud,which opens the valve. The valve is held close by spring pressure, whichholds the valve face against the seat for cylinder sealing.
Each cylinder in a typical V-8 engine has two valves, one intake and oneexhaust. And each cylinder needs two camshaft lobes to open the valves.One lobe opens the intake valve while another one close by opens theexhaust valve. As the intake cam lobe rotates against the lifter andopens the valve, the piston is beginning its journey downward in thecylinder bore. The open intake valve and descending piston work togetherto allow fuel and air to be drawn into the cylinder. As the pistonreaches bottom dead center, the intake lobe is ramping down, whichallows spring pressure to close the intake valve.
With our fuel/air charge poised for action above the piston at TDC, itis time for the piston to begin that journey back to the top of thecylinder. With both valves closed, this allows the piston to squeeze orcompress the mixture. The ignition distributor, which is tied to thecamshaft drive gear, fires the spark plug, which ignites the mixture.Contrary to popular belief, the mixture does not ignite with the pistonat top dead center. Ignition begins before the piston reaches TDC.
The igniting mixture creates heat and pressure, which drives the pistondownward in the cylinder bore, turning the crankshaft, giving us ourpower stroke. As the piston nears bottom dead center, the exhaust lobeis opening the exhaust valve to allow the super-heated gasses to escapeahead of the ascending piston. The camshaft has done its job. And itgets to do this 8 times with 16 valves.