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Bo's ready for the Big 10
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Discussion Starter · #1 ·
Dodge, GM, and Honda all have engines that shut down half the cylinders at speed. Logic would say they should also shut down the cylinders when sitting in traffic. Does anyone know if there is a reason they can't do this. I've been wondering whether they can't or won't. This came about from wondering why don't big trucks use cylinder shut. Since they get about 5mpg saving 1mpg would be huge over the course of a year.
 

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Not Wearing Pants
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Robsa said:
Dodge, GM, and Honda all have engines that shut down half the cylinders at speed. Logic would say they should also shut down the cylinders when sitting in traffic. Does anyone know if there is a reason they can't do this. I've been wondering whether they can't or won't. This came about from wondering why don't big trucks use cylinder shut. Since they get about 5mpg saving 1mpg would be huge over the course of a year.
The honda accord and civic hybrids shut down completely when the vehicle is stopped.
 

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Bo's ready for the Big 10
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Discussion Starter · #3 ·
blueguydotcom said:
The honda accord and civic hybrids shut down completely when the vehicle is stopped.
I'm talking about the non hybrids that have the cylinder shut down. My Pilot runs no 3 cylinders while I'm cruising but all 6 when sitting at a stop light. I would think that would be a perfect place to shut down 3 cylinders.
 

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Robsa said:
I'm talking about the non hybrids that have the cylinder shut down. My Pilot runs no 3 cylinders while I'm cruising but all 6 when sitting at a stop light. I would think that would be a perfect place to shut down 3 cylinders.
Maybe because at idle the car doesn't use as much fuel as it does at cruising speeds?
I'm not sure though i'm not a engineerer.
 

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mmm... carbs!
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I'd think that the amount of fuel saved isn't worth the effort. Also, a regular car battery probably doesn't have the juice to start the car 100 times in the course of stop and go traffic. Hybrids have much larger batteries and regenerative abilities from braking.
 

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Format c:\*.* /y
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Because at low engine idle speeds shutting down half the cylinders would make the engine rough as hell. The whole car would shake and generally feel like a piece of crap. Pull just one of your plug wires and see how well your car idles...
 

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Ubergeek
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Tangent said:
Because at low engine idle speeds shutting down half the cylinders would make the engine rough as hell. The whole car would shake and generally feel like a piece of crap. Pull just one of your plug wires and see how well your car idles...
Exactly. On the freeway, you've got plenty of power to rotate the "dead weight" of the shut down pistons. The cylinders do NOT shut down at idle or in traffic.
 

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M Mad
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Let's see. 4 cylinder engine at 2500 RPM fires 1250 times per minute or 21 times per second. Cut in half, still 10 times per second.

At 800 RPM it fires only 400 times per minute or a little over 6 times per second. Cutting half the cylinders would mean firing 3 times per second. Yeap, that would be rough.
 
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