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Old 02-20-2009, 11:30 PM   #1 (permalink)
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2 Cyl engine?

I appologize if this isn't the right spot for this, but I got to thinking about car engines the other day.

They have those vehicles with 8 cyl that shut off cylinders and run on 4 at highway speeds.

Well, I was thinking, even in rural areas, you spend a decent amount of time within village limits where the speed limit is often below 40mph and acceleration isn't all that important, but if you want to stay alive, I don't think a 2 cyl would work on the highway.

So, I wonder if it is possible to build a 4 cylinder engine that could be manually switched from 2 cyl or 4 cyl. I know I got a 4 cyl vehicle that gets decent highway mpg, but it burns gas accelerating. I know I can't build an engine myself, but I just theorize that for a small car, this could be good.

Another idea not related is to have the battery power the engine fan, not the engine like in cars I saw in the early 90's, except to have a switch to turn them off (when the car will just sit there or when you are working on it.)

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Old 02-21-2009, 12:10 AM   #2 (permalink)
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"So, I wonder if it is possible to build a 4 cylinder engine that could be manually switched from 2 cyl or 4 cyl. I know I got a 4 cyl vehicle that gets decent highway mpg, but it burns gas accelerating. I know I can't build an engine myself, but I just theorize that for a small car, this could be good."

I know the OEMs are looking into it. I suspect the holdup is excessive vibration in 2 cyl mode and an unwillingness to add enough flywheel to smooth it out.

"Another idea not related is to have the battery power the engine fan, not the engine like in cars I saw in the early 90's, except to have a switch to turn them off (when the car will just sit there or when you are working on it.)"

Ummmm... have you looked under the hood in the last 25 years? Pretty much all electric fans except pickups.
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Old 02-21-2009, 12:27 AM   #3 (permalink)
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Haven't looked under the hood of a car much. I've got a pickup (a small one ), assumed that all fans were like that, didn't really think that one out. Haven't been under a car in ten years, and haven't heard any fans running lately, thought maybe they changed things.

The excessive vibration is what I thought would be the biggest problem too for running on 2 cyl.
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Old 02-21-2009, 03:30 PM   #4 (permalink)
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the civic hybrid switches between being a 4 cylinder and a single cylinder engine by disconnecting it's rocker arms in a similar way as the v-tec engines work, with a hydraulic operated pin that slides to connects the two halves of the rocker arm.
Main reason pickup trucks have mechanical fans is that they are designed to spend alot of their life under load, so the fan would be running alot of the time any way, because trucks should not be used as passenger vehicles, they are utility vehicles.
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Old 02-21-2009, 05:31 PM   #5 (permalink)
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To allow a car to shut off a number of cylinders, you need to know how much power the car needs when cruising.

If for example, it was a light car and only needed the power of 2 (Out of its 4) cylinders when cruising, then deactivating the other 2 would work.

However, if you deactivate too many cylinders, the car will not have enough power to cruise - like throwing your car in 5th at 20mph, it might keep going, but it wont like it.


About the vibration issue... VW, Porsche and Subaru have your answer. Flat 4/6 cylinder engines, by design they are almost perfectly balanced. Deactivating 2 out of 4 cylinders would not cause any extra vibrations.


Last edited by vinny1989; 02-21-2009 at 05:32 PM.. Reason: Cant spell
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