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SVTPerformance's Chain of Restaurants
Road Side Pub
How does Cylinder Deactivation actually save fuel?
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<blockquote data-quote="James Snover" data-source="post: 15766004" data-attributes="member: 67454"><p>What he said. Dead on 100% correct.</p><p></p><p>An engine of a particular displacement has to have a certain amount of fuel to meet the air-fuel ratio requirements for good burning. Too lean or too rich, and emissions go right through the roof, and too lean also makes the engine run hot. Fuel economy falls off, as well, almost as much when lean as when rich, ironically.</p><p></p><p>So, your Chevy 350 V8 has to make 20hp to make you go 65mph. But since those 350 cubic inches of volume require a specific minimum quantity of fuel to ensure the proper air fuel ratio, you have an engine that makes 150hp, 130 more than you need. The only way to reduce the quantity of fuel is is to reduce the amount of displacement to which you need to add enough fuel to hit the magic air-fuel ratio number.</p><p></p><p>Now, there is a better way to accomplish the same thing, with real-world improvements in fuel economy far better than cylinder deactivation:</p><p></p><p>For normally aspirated engines, it's the Atkins-cycle, for supercharged engines, it's the Miller cycle. By altering the intake valve timing you can leave the intake valve open at different times in the intake cycle, so that some of the air your cylinder just took in is pushed back out. When the intake valve closes late, you have a correspondingly smaller charge of air to which to add fuel to get the proper air-fuel ratio. The only loss here is a slight plumping loss, with a long list of benefits, including keeping the whole engine up to operating temperature.</p><p></p><p>These cycles both require variable cam timing and direct cylinder injection of fuel to be truly useful. Now that both of those items are reality, many automakers are incorporating them into their engine management systems.</p></blockquote><p></p>
[QUOTE="James Snover, post: 15766004, member: 67454"] What he said. Dead on 100% correct. An engine of a particular displacement has to have a certain amount of fuel to meet the air-fuel ratio requirements for good burning. Too lean or too rich, and emissions go right through the roof, and too lean also makes the engine run hot. Fuel economy falls off, as well, almost as much when lean as when rich, ironically. So, your Chevy 350 V8 has to make 20hp to make you go 65mph. But since those 350 cubic inches of volume require a specific minimum quantity of fuel to ensure the proper air fuel ratio, you have an engine that makes 150hp, 130 more than you need. The only way to reduce the quantity of fuel is is to reduce the amount of displacement to which you need to add enough fuel to hit the magic air-fuel ratio number. Now, there is a better way to accomplish the same thing, with real-world improvements in fuel economy far better than cylinder deactivation: For normally aspirated engines, it's the Atkins-cycle, for supercharged engines, it's the Miller cycle. By altering the intake valve timing you can leave the intake valve open at different times in the intake cycle, so that some of the air your cylinder just took in is pushed back out. When the intake valve closes late, you have a correspondingly smaller charge of air to which to add fuel to get the proper air-fuel ratio. The only loss here is a slight plumping loss, with a long list of benefits, including keeping the whole engine up to operating temperature. These cycles both require variable cam timing and direct cylinder injection of fuel to be truly useful. Now that both of those items are reality, many automakers are incorporating them into their engine management systems. [/QUOTE]
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How does Cylinder Deactivation actually save fuel?
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