Shade tree cylinder deactivation?

[roflwaffle]

I've seen this idea tossed around the web, supposedly w/ some success w/ V engines. I'd love to see it done w/ my V6 sedan, since it would allow me to cruise at a relatively slow speed where possible (~45-55mph) w/o being in an undesirable portion of my engine's BSFC map. The downside to doing it this to a vehicle not designed to close the cylinders, aside from the possibility of undesirable vibration, would be too much cooling of the deactivated bank from the continuous air at whatever the outside temperature was.

My question is, would jerrying a system similar to Toyota's TVIS in order to close the intake runners to the deactivated cylinders result in the bank staying hot enough from the exhaust to avoid significant wear, or is trapping the hot exhaust from the last power stroke charge in the cylinder needed for that?

 

[patprimmer]

Is the gain because it is only using 4 cylinders instead of 6 to produce the same performance or because you are throttling back to keep it on 4 cylinders and accepting a lower performance while doing so

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[cibachrome]

I'm accepting the reduced performance to keep the motor in 4 cylinder mode. That means accepting the speed reduction on hills and longer 0 - 55 mph run times. FYI there is also a tire pressure component to this. If I run 30 psi in the tires (35 is standard), it hardly ever drops into 4 cylinder mode. If I run 45 psi, it can stay there much longer for the same road course. Many of us are begging to have a switch on the dash to select cruise mode (favors 4 cyl) vs launch mode (favors 0 to 60 or whatever). There may be an emissions component to this, but I know for a fact that powertrain vibration is also a dominant weighting factor in the tuning of this system. I'd really like to know if premium fuel is a benefit, but it takes too long for the ECM to learn about the type of fuel it has available. Yes, there's a repeatable element of fuel brands, based on my many miles on company cars with the AFM driving the same route for too many years.

 

[patprimmer]

So a light triggered by inlet manifold vacuum could have the same effect if calibrated to come on at the same load and other parameters and habits were the same.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[BrianPetersen]

I suspect a good portion of that 44% improvement is due to driving gentler and slower, and COULD also be achieved without the cylinder de-activation scheme ... and the gain would possibly be even greater if the truck only had those 4 cylinders without the extra friction of the 4 that are being dragged along!

(I've driven a Toyota 4-Runner with a 2.7 litre 4 banger, and it was fine)

 

[ivymike]

26mpg is pretty good for a tahoe... I had a 4cyl ford ranger that would get 27mpg in the summer and 24mpg in the winter. It was lighter and smaller, and had a 5spd manual trans.