Running on 4 cylinders

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Apr 20, 2006 | 03:27 PM

robin427

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Running on 4 cylinders

I see GM are looking into a system that shuts down half the cylinders whilst cruising to save gas. In theory, I'm not about to do it, would it harm the engine if a switch was installed that cut the power to 4 of the injectors and coil packs?

Apr 20, 2006 | 03:33 PM

Patrick G

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You would have to remove the pushrods on 4 of the 8 cylinders and kill the fuel injectors to those cylinders. You could still run the spark if you wanted to, but it wouldn't be needed. This is possible with a cam that generates a high vacuum signal (stock cam), but the motor would REALLY be a slug on 4 cylinders if you ran a performance camshaft, LOL. No bottom end torque AT ALL!

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Apr 20, 2006 | 03:40 PM

robin427

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Why would you have to remove the pushrods? We've all turned our engines over without any fuel in them, or would the high revs damage the engine due to the lack of resistance from the exhaust gases?

Just a theoretical question, although with gas being $1.70 a litre this side of the pond, it's worth thinking about economy.

Apr 20, 2006 | 04:17 PM

Patrick G

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You want to have the valves closed, otherwise, you're spending lots of energy on a compression stroke that makes no power. With the valves closed, the piston compresses the trapped air like a big coil spring. This is why displacement on demand closes the valves.

Apr 20, 2006 | 07:33 PM

toecutter_tx

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Try disconnecting an injector and I bet you throw a code for a misfire.
Ask me how I know.

Apr 21, 2006 | 03:16 AM

robin427

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Nobody said it would be easy... I suppose you'd need electronic valves, like the Honda VVT to make it feasible...

Apr 21, 2006 | 01:35 PM

squealingtires

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My understanding of GM's displacement on demand is that GM has put provisons in the LS2 blocks to allow passages for oil to the lifters. The lifters fill with oil and expand allowing the valves to function. When running on 4 the lifters collapse which causes the valves to remain closed. It is all controlled by valves which direct flow into the lifters.

Is this how it works?