Let’s say you’ve got a 3-liter V-6. Why not unplug the injectors for the 2 middle cyls. and save some gas for highway driving. You could run them thru a 2-pole relay w/ dashboard switch for passing, hills., etc. The only problem I can see is maybe the crank counterweights would get “confused” and cause vibration. Is this true? If so how much? Somebody must’ve tried this before.
You’d still have a lot of frictional and pumping losses because those two cylinders are going through the 4 cycles of the engine.
The compression/power stroke with no power would likely erase any benefits you would find by doing this.
There’s a reason it’s taken so long for a decent cylinder deactivation system to come into place.
Yeah. GM did it on the Northstar V8 series of engines. Honda’s doing it now on the Accord V6. The Northstars were pretty good, but Honda is having some oil loss issues as the oil seeps past the seals in the non-firing cylinders. It’s not a huge deal, and well within the “1qt per 1000 miles is normal” standard. Northstar took the idea a step further and was capable of running 4 cylinders at a time, and swapping to the other 4 from time to time, which kept things cool enough to limp to a garage if you lost coolant.
Of course, these engines skip the dashboard switch - they just look at the throttle position. If you hit the gas, they turn on the deactivated cylinders.
Shutting off the fuel is not the same as the cars with selective cylinder deactivation. On all of those not only is the fuel injection shut off, the valves are shut, so that the inactive cylinders act as springs. Without the valve shut off your mpgs will get worse, not better. And there’s no way to make that modification yourself.
As the others have said, the systems that do this are complicated and, actually, have experienced some problems with uneven temperatures. And one other problem you’d have is…do you know when in your crank rotation your cylinders fire? Would you be able to disable two plugs and have the remaining four cylinders fire at equal crank angles…like every 90 degrees or every 60 degrees? Or every 180 degrees? Do you even know?
If you have an old beater with a V6 it might be an interesting project to experiment with. But I’d be inclined not to try it with a vehicle that you need for a reliable daily driver.
If it’s a modern car with an O2 sensor pumping all that air into the exhaust will throw everything out of whack.
Sure it’ll save gas!
While your car is in the shop getting a new engine put in it, it won’t be using ANY fuel at all. 
Worth a try as long as you can disable the system and return to normal at the flick of a switch. In most engines that disable cylinders I think they open the valves to reduce friction and compression. But in a motor running at 1,500 rpm and above you might save some fuel without the special valve mechanism.
Nope, they close the valves to eliminate pumping losses. By having the valves closed the air acts like a spring. The compression’s ok, because that energy is returned when the air pushes the piston back down. Without that valve closing mechanism, the losses will continue, regardless of rpms, I’d think about a pretty much constant %. So high rpms will result in high losses.
If all it took was to shut off the injectors to save gas, that $1 programming step would have already been taken.
It was done back in the 80’s by Cadillac. It worked some but was more expense and bother than what it was worth. With today’s fuel injection and computer control, the computer is already leaning the fuel out as much as possible for maximum economy.
I see little practical benefit with many down sides including complexity as Bing and most have pointed out. More efficient use of the fuel going to all of the cylinders with present approaches and future laser technology as we discussed earlier are better “plans” in my opinion. Operating an engine at it’s most efficient average range and letting electric drive motors handle the acceleration and hill climbing change is another. I feel this is the next untapped future of the ICE allowing for smaller engines to begin with instead of playing musical chairs with the cylinders. You won’t see the simple and elegant solutions as complexity hides the profit margins necessary for automobile manufacturers to survive while simplicity would mean their down fall.
Perhaps an engine with two cranks?
A straight or flat 6 with two short cranks in line 3 cylinders each.
Some kind of ratcheting and controlled slip coupling between the two.
Twice as many cams too.
One of the Italian makers would like that idea.
Interesting ideas. Perhaps we’ll see one of them in the future.