can I run on 4 cylinders on the highway?

[TaraFirma]

Basically, I'd like to know if anyone has figured out a way to run a V8 on 4 cylinders(firing every other cylinder) at highway speeds to increase fuel economy. Chevy has done it. Can it be done with the AEM?
eg. At speeds obove X with engine load below Y every other cylinder would be fired, with the 4 not fired being fired on the next rotation.
For the mustang: 1,7,6,4 then 3,2,5,8 on the next crank rotation.
If it can be done, How? If not can it be suggested to AEM to add it as a software download.

[tony]

Sounds good on paper, but without hanging exh valves open on the disabled cylinders, the benefits would be minimal...the fuel you save on the 4 disabled cylinders would be used by the other 4 to drive your 4 "air compressors".

Tony

[trbo2dr]

i've never really thought about this until seeing this thread but i don't think it'll work for another reason.  if it takes 50 hp to keep your vehicle moving at a sustained cruise then it doesn't matter if you have 4, 8, or 16 cylinders.  it still takes the same amount of fuel to make 50 hp regardless of the number of cylinders you have, right?

[Vitor]

Basicly true, but more moving parts = more friction.

On those engines, they have capability to hold valves open, so you decrease your pumping loses.

V

[tt460]

The most common factory cylinder deactivation is done through the valvetrain.  Either special lifters or rocker arms are utilized that have a latching mechanism that "disables" the valve event and keeps the engine valves closed when not needed.  They do this because otherwise you'd be doing work by pumping air mass through the engine and not doing anything with it.  Pumping air that's not used in the combustion cycle = Wasted work = Less efficiency.

That being said: Cylinder deactivation that utilizes holding intake/exhaust valves closed and eliminates the wasted work of pumping air on each cycle still only improves fuel economy by about 5%.

Deactivating cylinders by turning fuel off alone will yield gains much less than 5% as the engine will still need to pump air.

[JulianSerna]

I did this using a PMS module and it did save me about 20% on gas. However, the only reason it worked on me was that I had a 427 on my Mustang, so I had more torque than I needed. However, I had to relocate my O2 sensors up near the cylinders that would always fire, else the ECC would read a lean condition from all that extra air being pumped out and would try to compensate by running the remaining cylender rich. It was a fun experiment, but without the actual valves deactivating as well, it has minimal use. Also, I did not have the option of turning all cylenders back on once I floored the pedal.