Cylinder Deactivation

[GasSavers_Bruce]

...and deactivated cylinders separated by two strokes instead of one.

My car probably wouldn't work well for this, since it's an automatic; with more throttle, the ECM unlocks the TCC clutch and FE goes to Hell. Any efficiency gains would be soaked up by the torque converter.

[GasSavers_Bruce]

...and deactivated cylinders separated by two strokes instead of one.

My car probably wouldn't work well for this, since it's an automatic; with more throttle, the ECM unlocks the TCC clutch and FE goes to Hell. Any efficiency gains would be soaked up by the torque converter.

[omgwtfbyobbq]

Yeah... That's the problem with automatics and their kick-down crap. In a situation like this turning it off from the cab would be the best bet since the driver could cut fuel under low load/flat ground/low speed, so the automatic wouldn't upshift. But, this is something that's ultimately best for a M/T... Sure wish my pickup wasn't carb'd, I bet this could result in some serious FE increases with the right setup.

[GasSavers_Bruce]

I mentioned earlier that my `78 (carbureted) Malibu got its best mileage with a couple of cylinders effectively deactivated by worn-out cams...if you wanted to simulate this on your P/U and can tolerate a serious decrease in power, just pull the rocker arms on a couple of cylinders. If it won't start, pull the plugs on those cylinders as well.

You may want to try pulling plug wires on a couple of cylinders first to verify which pair gives the smoothest operation.

[skewbe]

re: deactivating cylinders, seems to me that a flat 4 engine could be split into two flat 2 engines that had a clutch (or in-out box) between them that are both reasonably balanced in themselves.

[omgwtfbyobbq]

So I can do this with a carb'd engine? Does the carb just mix a certain amount of fuel with a certain amount of air, so with two valves not opening, the carb just won't mix any fuel in? Regarding ECUs, they're kinda wonky ime. For instance, it took ~50-100 miles for the CEL to go off when I hadn't properly installed my heated O2 sensor. I was able to pass smog by reseting the ECU a day before the check.

[GasSavers_Bruce]

Originally Posted by omgwtfbyobbq

So I can do this with a carb'd engine? Does the carb just mix a certain amount of fuel with a certain amount of air, so with two valves not opening, the carb just won't mix any fuel in.

The carb just sits on top of the engine and mixes air and fuel. It doesn't care much where it goes.

Originally Posted by skewbe

re: deactivating cylinders, seems to me that a flat 4 engine could be split into two flat 2 engines that had a clutch (or in-out box) between them that are both reasonably balanced in themselves.

GM did a concept car based on this a few decades back, though it was two larger engines instead and each was at a different end of the car to optimize F/R weight ratio. The main problem was that the second engine, which was only used for acceleration, was always too cold to work efficiently.

[omgwtfbyobbq]

Sweet. And I just need to make sure that I'm deactivating two cylinders that move together, like 1 and 4 or 2 and 3.

[GasSavers_Bruce]

That'd be my recommendation.

I'd tend to think deactivating 1 and 4 would be preferable over 2 and 3; 2 and 3 should run a bit hotter than 1 and 4, since they're adjacent to each other, and engines like to run hot.

Like I said, try pulling some plug wires first and trying some different combinations before you commit to minor surgery. You may decide that even if you use the correct 2 cylinders, it's still too rough or underpowered.

[Gary Palmer]

Having traveled this road and beat it up pretty badly, here's my 2 cents.

First, just eliminating the ignition to one or more cylinders doesn't do anything except make the car run like garbage.

Second, in order for this to work, you have to disable the valves opening and closing on the cylinder or cylinders which you are attempting to disable. However, pulling the pistons is a problem because crankshafts have oil journals from one crank to the next. If you pull a connecting rod and piston, you will lose your oil pressure and syanora. (Don't know the spelling) If you pull your rocker arms, you have the same fundamental problem, they rocker arm is hollow, allowing oil to flow, under pressure, to all of the rockers. If you pull a rocker, again, no oil.

Their are at least two possible alternatives, although I'm sure their are more.

One, if you remove the rocker, replace the rocker with a modified rocker, which is shortened on both ends, to maintain the oil pressure. This presumes you do both the intake and exhaust valves, on any given cylinder.

Two, if you took a VTEC engine, maybe you could get the camshaft reground, to allow the timing to stay the same, but just disable one or two of the cylinders. I believe this is what Honda is probably doing on their V6 engines

Short of those two, or something similar, just eliminating the fuel or the ignition to the cylinder is just going to give you a rough running engine.