Then the exhaust valve would open right as the piston bottoms out at the end of the combustion stroke and would close as the piston completes the exhaust stroke.
The intake valve would close right as the piston bottoms out. Next Up " ".
At low engine speeds, this rocker is not connected to any valves. Share Facebook Tweet Pinterest Email. Therefore, at higher rpm ranges you want the intake valve to open prior to the intake stroke -- actually back in the exhaust stroke -- so that by the time the piston starts moving downward in the intake stroke, the valve is open and air moves freely into the cylinder during the entire intake stroke.
A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam. Variable Valve Timing. In this way, the engine gets the best features of low-speed and high-speed camshafts in the same engine.
How does the engine know what profile to engage and when? The shape of the cam smoothly blends these two profiles together.
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Instead of having just one lobe profile for its camshafts -- it has two. Image Gallery: More to Explore.
Car news, reviews, motorsports, auto shows and stunning photography delivered right to your mailbox. Subscribe Today. The opening and closing times can be shifted using a mechanism that rotates the cam ahead a little as it spins.
This is something of a simplification, but you get the idea. Several engine manufacturers are experimenting with systems that would allow infinite variability in valve timing.
The shaft still spins just like a regular camshaft -- but by gradually sliding the camshaft laterally as the engine speed and load increase, the valve timing can be optimized. Is there a difference between inline and V engine configurations? Digital Subscription Take Autoweek to go on your digital device and get the car news you want, wherever you are.
For maximum engine performance at low engine speeds, the valves need to open and close differently than they do at higher engine speeds. Will new motor mounts increase engine response? When the intake valve opens right at the top of the intake stroke, it turns out that the piston has a lot of trouble getting the air moving into the cylinder in the short time available a fraction of a second.