Cylinder Shutoff

[BigDaddyO]

OK, so I may not know alot about cars but here is a question that I have been wondering for a while.

If you have a v6 engine, why can't you physically disable two of the cylinders and basically get a 4cyl engine? Newer v8 engines can do this automatically on the fly so you would think doing it permanant like should be fairly easy.

Mike

[Daox]

There was a fairly long thread on cylinder deactivation. Check it out here:

http://forum.ecomodder.com/showthrea...ssion-968.html

[thebrad]

I was discussing this with my auto shop teacher last week and basically you need a V formation engine so that it will remain balanced when you deactivate the cylinders. I didn't take it any further than that because I have an inline 4, but if it was to be a backyard project I am not so sure it's easy as pulling the spark plugs because I think the ECU would still be telling the injectors to send gas in there.

[thebrad]

I was discussing the Tahoe Hybrid with a Chevy tech this evening and it seems that the the ECU disengages the lifters for those four cylinders. The engine uses push rods, but the tech theorized that it could be applied to an OHC engine as long as it had rocker arms near the lifters that would allow for the lifters to disabled (sounds like it wouldn't work on a Honda/Toyota). Some other worlds were mentioned, but I don't remember the specifics.

[cfg83]

thebrad -

I learned from Frank Lee that the old VW Bug flat-four boxer engines are naturally balanced, so they would be a candidate. This makes me theorize that the Subaru boxer engines are also candidates for cylinder deactivation.

CarloSW2

[RH77]

Trust me on this...

I tried it on an I-4, it didn't work, and used more fuel.

On later engines, the Fuel-Injection system (and oxygen sensor feedback loop) requires a pre-determined ratio. If you override this, it might benefit, but...

You'll have hot and cold spots and pumping losses. An engine swap is easier...

RH77

[thebrad]

I'm not interested in doing this to my Civic, I have too many hills in my area. I just think it's interesting technology to discuss.
They introduced it in the 70s and it was all mechanical (thus heavy, tedious to work on, and unreliable) now GM are using it through an electrical application with solenoids. I am kind of curious how the Accord works, probably the same principle, but eh.
Very interesting stuff.

[Andyman]

I tried cylinder deactivation on three vehicles I've had. The engines were a 5.8 L V8, a 4.3 L V6 and a 2.0 L inline 4 cylinder. Only the V8 conversion really worked well. The highway fuel economy went from 18 MPG to 24 MPG. It was sluggish at getting moving from a stop but the power was good enough above 30 MPH. The engine had a performance camshaft which reduced low speed torque.

The easy way to do the conversion is to remove either the pushrods or the rocker arms (if the engine is overhead cam) in every other cylinder in the firing order. On a V6 this means disabling three cylinders on one side. If four cylinders were running, the firing pattern would be more uneven and there would be more vibration. If the engine has multiport fuel injection, the unused cylinders should have their fuel injectors disconnected by unplugging the electrical connectors.

When I tried the experiment on a V6 Astro van, I just removed the six pushrods on the right side of the engine, reinstalled the valve cover and disconnected one of the two fuel injectors on the the throttle body fuel injection unit. I depended on some varnish buildup on the valve lifters to make them stick in the lifter bores above the camshaft without falling out. A new engine would have required removal of the intake manifold to hold up the lifters with hose clamps. I was not satisfied with the results for three reasons.

1) The starter motor had trouble starting the engine when hot because there were two compression strokes at a time.
2) The engine torque was not sufficient to climb up a steep driveway in reverse.
3) The worn timing chain rattled more because of fewer valve lifters pushing on the camshaft. Therefore the torque to turn the camshaft was more uneven.

In about an hour I restored the van to work on six cylinders.

I also converted my Accord to run on two cylinders. It worked pretty well that way but accelerating required some patience. It moved like a bus. It did a good job cruising on the highway as long as I was satisfied with 60 MPH. Higher speeds would have required downshifting to third gear. There didn't seem to be much fuel economy improvement, at least in local driving, and the extra vibration at low engine speeds was damaging exhaust parts. I restored it to four cylinder operation after about 700 miles.

I've decided that cylinder deactivation is a good idea if it can be switched on and off automatically while driving. It would be useful to have a kit to allow this modification on older six and eight cylinder engines. My test showed that it can improve fuel economy by 33% on a V8 car.

[MetroMPG]

Originally Posted by RH77

Trust me on this...

I tried it on an I-4, it didn't work, and used more fuel.

On later engines, the Fuel-Injection system (and oxygen sensor feedback loop) requires a pre-determined ratio. If you override this, it might benefit, but...

Resurrecting this thread to add more information to the pile. Someone tried the same thing you did, Rick, and had the same results:

I installed a switch which allowed me to turn off two of the fuel injectors on the 2.0L DOHC 4-cylinder in my Escort ZX2 (cylinders 2 and 3). I drove for 1,300 miles on my normal commute (about 90% highway), with two fuel injectors switched off at highway speeds, and switched back on for city driving. Surprisingly, my data showed a clear fuel economy penalty for injector cut-out! My fuel economy was about 2% to 4% worse than the normal driving before and after the experiment.

More information on his web page: Other Experiments

[Christ]

The "more information" point gets stressed here... the cylinder deactivation technology currently available for the larger engines shuts down the cylinder's fuel supply, removes access to intake and exhaust via the valves, and parses the sensor signals to accommodate for the decreased airflow and other outputs.

FYI.