Thread: How does it work??.Dropping cylinders

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You know the newer cars,some drop cylinders to save on gas mileage.I am curious about how they work.Why isn't that felt as a miss??.If they save on gas,I am guessing the system that controls shutting down the cylinder shuts off the fuel and spark.I do know it involves throttle position.Wonder if they really do work or if those engines have problems like fouled plugs more often,etc.

Also-if anyone has heard of a aftermarket system for use on the earlier engines??.You know like SBC's.Wouldn't that be cool to have a system like that on your hot rod??.Cruise mpg in the upper 20's.

Hummm-if cylinders are being dropped,wonder why the other cylinders aren't eating more gas to pick up the lack of power??.

Gary,
Isn't this what they called "Variable Displacement", as in the Cadillac V8-6-4 back in the 80's? Those worked by disabling the lifters so that both the intake and exhaust valves stayed closed when the engine was lightly loaded, but they came back in under acceleration. Here's a link that explains the details, and it does mention an aftermarket supplier that tried it for a while. Variable displacement - Wikipedia, the free encyclopedia

Hey Roger,

The link didn't go threw.Caddy is one of them.I think some others have used that system.

I was overseas at the time but I recall reading about the systems back then, as I recall Ford also had a similar system (at least in development) also.

While the idea may have been sound, the technology at the time was not advanced sufficiently to really make it workable (kind of like comparing the old mechanical Rochester or Bendix fuel injection systems to today’s fuel injection).

Although variable displacement might be an interesting exercise in engineering, the goal of upper 20’s for fuel mileage should be pretty easily obtainable with a well thought out drive train and engine build without the added complication (especially if you’re talking about using a SBC).

Originally Posted by 1gary

Hey Roger,

The link didn't go threw.Caddy is one of them.I think some others have used that system.

Gary,
Not sure why the link does not work for you - I click it and it opens the window in Wikipedia. Maybe cut & paste it in your browser? The article points out that Cadillac had their try in '81 but it caused them all kinds of warranty problems. Mitsubishi had a version a year later, and it fell out of use until Mercedes brought it out on a V-12 in the '90's, followed by Chrysler on the Hemi's in '04. With oil prices in '08 "...many manufacturers..." turned to variable displacement controls on their larger engines to bring their CAFE numbers down, and to offer more fuel efficiency. Here's the link again - http://en.wikipedia.org/wiki/Variable_displacement

I've got that on my '09 Avalanche. It was standard equip on the 5.3 LS engine. Basically the computer shuts off the spark and injectors to 4 of the cylinders (no 6 cylinder step). It's virtually seamless when it happens. If I choose the computer readout on the dash I can watch when it switches mode, but other than that there's no feel to it. On my rig you pretty much need to be on dead flat terrain, or downhill, for it to be active. Throttle position is probably part of the data input the computer considers, but there are likely more data points that contribute to the calculations. I wouldn't imagine that fouling the plugs would be a consideration as there's no fuel to be burned when the cylinder is shut off.

Originally Posted by Bob Parmenter

I've got that on my '09 Avalanche. It was standard equip on the 5.3 LS engine. Basically the computer shuts off the spark and injectors to 4 of the cylinders (no 6 cylinder step). It's virtually seamless when it happens. If I choose the computer readout on the dash I can watch when it switches mode, but other than that there's no feel to it. On my rig you pretty much need to be on dead flat terrain, or downhill, for it to be active. Throttle position is probably part of the data input the computer considers, but there are likely more data points that contribute to the calculations. I wouldn't imagine that fouling the plugs would be a consideration as there's no fuel to be burned when the cylinder is shut off.

The more complex computer controls coupled with direct port injection being much more common today make this a lot more manageable animal than it was in the '80's and '90's. The mechanical approach before was much more prone to problems. One thing that was a surprise to me was that by keeping the valves closed the trapped gasses in the cylinder are alternately compressed and expanded with the cylinder action, but the forces balance out with no work being added to the cycle. That said, it seems to me that an aftermarket application, with all of the needed inputs and logic, would be difficult to install and optimize on an older, non-computer controlled driveline.

Originally Posted by Bob Parmenter

I've got that on my '09 Avalanche. It was standard equip on the 5.3 LS engine. Basically the computer shuts off the spark and injectors to 4 of the cylinders (no 6 cylinder step). It's virtually seamless when it happens. If I choose the computer readout on the dash I can watch when it switches mode, but other than that there's no feel to it. On my rig you pretty much need to be on dead flat terrain, or downhill, for it to be active. Throttle position is probably part of the data input the computer considers, but there are likely more data points that contribute to the calculations. I wouldn't imagine that fouling the plugs would be a consideration as there's no fuel to be burned when the cylinder is shut off.

I am guessing it would involve the VSS,throttle position sensor,timing,some how adjust the spark advance and fuel curve,convert to a 4 cylinder firing oder,maybe the o2 sensor,............?????.

Lots of computing power in the modern engine.......

With electronics where they are today, I have wondered why the have not gone to solenoid actuated valves instead of cam driven. You would think that would help in the fuel and exhaust management instead of the lifter thing.

Originally Posted by rspears

Gary,
Not sure why the link does not work for you - I click it and it opens the window in Wikipedia. Maybe cut & paste it in your browser? The article points out that Cadillac had their try in '81 but it caused them all kinds of warranty problems. Mitsubishi had a version a year later, and it fell out of use until Mercedes brought it out on a V-12 in the '90's, followed by Chrysler on the Hemi's in '04. With oil prices in '08 "...many manufacturers..." turned to variable displacement controls on their larger engines to bring their CAFE numbers down, and to offer more fuel efficiency. Here's the link again -
Variable displacement - Wikipedia, the free encyclopedia

Roger,you first posted link is there.It was my mistake looking for a www. ref.

We all have looked at add-on's like propane,natural gas,hyrogen,Gear Vendors O/d's,etc to save on gas mileage.Many having big downsides.So for me to understand these systems more completely wouldn't be a bad thing.I just think when you consider what Edelborck has as a aftermarket add-on done with their EFI systems although very expensive,maybe a conversion for this is out there.But as I said above,first I need to understand them better and as with everything,there is a up side and a down side.

sfort......solenoid reaction time is too slow to work well. AND, to get the force, the current draw would be horrendous. Solenoid valves run in the 60-70 Hz reaction time.....a 6000 rpm engine has a valve event at about 500 Hz rate but, in reality, it is much faster since part of the time, the valve is held open. Formula cars have pneumatic valve actuators but dont use solenoid valves in the air circuit because they are too slow also. Plus, the formula cars have extremely lightweight valve trains with ultra small and light valves.

The Displacement on Demand (DOD) system on late model GM's uncouples the intake hydralic lifter by use of a solenoid in the oil/lifter galley. The lifter body still travels up and down in its bore, but the lifter is uncoupled, and the valve spring tension keeps the plunger and pushrod in place. The DOD lifter also have a spring to keep tension on the plunger, much like a roller cam rev kit.The exhaust valve is still opening/closing to keep the cylinder from becoming an oil pump, but with no air/fuel mixture to ignite since the injector is shut off, the cylinder has no output. The coil still fires to keep the cylinder clean (valve overlap, exhaust manifold backpressure, etc). The 'puter modifies the timming curve and controls the advance/activation of the DOD engine/system.
The 4-6-8 Caddy used a different system. They uncoupled the rocker arm so that the rocker pivot would move from the center of the arm in coventional form, to the pivot point being at the valve. The lifter still moved the pushrod, and the rocker arm would move, but with the pivot point at the valve, no air/fuel entered the cylinder. The solenoid was mounted directly over the rocker arm in the valve cover. The biggest problem with the system was the Bendix computer. Lots of things have changed in forty years !