Permanent cyl deactivation

[t vago]

So, you've actually done this, then? You've actually ran an engine with 1/2 of its injectors and/or spark plugs not firing? It isn't all that hard to do, you know, to spoof the O2 sensor into not seeing the excess oxygen being pumped into the exhaust stream by the non-working cylinders.

Originally Posted by arcosine

He is not taking into account the lower manifold vacuum due to the 2 active cylinders working harder to keep up, the engine would be at full throttle twice as long with half the cylinders. I would go as far to say that under load it would have half the manifold vacuum and thus half the pumping loss. Of course if the valves were deactivated then it would have half the vacuum and half the displacement for 1/4 the pumping loss of a full engine.

Where did you get your numbers?

[arcosine]

yes I have, both ways.

[t vago]

So, as you say I am not taking into account the thing that you said about higher intake manifold vacuum being a result of shutting off injectors/ignition to half the cylinders in a given engine, you're implying that merely shutting off the injectors/ignition to said cylinders is actually going to lead to worthwhile fuel economy savings.

Would you care to enlighten us with A-B-A testing data showing this to be worthwhile? And are you currently using this method?

[arcosine]

You have it backward, the manifold vacuum is lower, meaning more pressure, less vacuum. I am not here to prove anything, just relating my experience. Turning the rocker arms up on two cylinders on my 1977 honda CVCC gas mileage increased from 40 to 48 mpg but a loaded semitruck could out accelerate the now 800 cc motor. I had to turn the idle down since it was also nearly twice the RPM.

I ran a 1993 saturn sw2 on 3 cylinders for a while, since it automatically converted itself when the injector #3 went bad.