Quote:
Originally Posted by t vago
I would have probably just ground down the camshaft for the valves associated with cylinders 1 and 4. That is, assuming that the valves were directly driven off the camshaft instead of using a rocker arm or some other method of articulation.
The pistons inside cylinders 1 and 4 would effectively turn into springs, as they continually compressed and then let expand the air trapped inside them. You would also still have all of that mass to offset the 180 degree out-of-phase mass of the pistons and conrods for cylinders 2 and 3.
|
Dear MetroMPG,
I greatly appreciate your response. In response to what you have expressed, I had the same thought process and indeed have attempted this same experiment/modification already on a 1986 Nissan Sentra wagon. That car, which has a favorable stroke to bore ratio, as Nissan's typically do, had solid rocker arms and a single overhead cam. In order to deactivate the valves on pistons 1 & 4, I cut and ground the rockers so they were only a spacer keeping the rocker assembly in proper spacing. Valves for pistons 1 & 4 were no longer actuated as the rocker arms were nothing more than sleeves/cylinders on the rocker shaft when I was done with them.
I anticipated that the pistons with the deactivated rockers would act like air springs.
What I found was the engine was very under powered... almost undriveable. There was a narrow RPM range in which it produced enough power that the car could run safely, however it was overall very poor performance.
I theorize that the "air spring" effect is actually more complex than the initial conception realizes. What I mean by this is that in consideration of fluid dynamics/acoustics, there must be very specific RPM in which the pressure wave inside the cylinder is not working against the deactivated piston. At the speeds that the piston is moving, the resistance of an air pressure wave can be considerable. With respect to wave mechanics, you may generally have constructive interference or destructive interference in considering the phases of the oscillations in whatever system you are working with.
In short, I found the engine could not perform suitably.
It is possible either the engine or transmission were already worn beyond a usable limit, however before I modified the engine I did drive the car and it seemed to operate reasonably. I also always make sure to refresh the transmission whether it is an automatic or manual with fresh fluid/oil.
Also, I am aware that several manufactures have incorporated this "cylinder deactivation" feature in their engines.. so that 8cyl engines can operate as 6 or even 4 cylinder engines via control of a computer. It seems that friction effects are probably significant enough that benefit from this feature is minor or negligible. I have seen no hard evidence that cylinder deactivation or the air spring effect offers useful results, either in literature or from my own experimentation.
Again, I am only one data point. Maybe it is worth repeating this experiment.
Thank you for your response MetroMPG.
-Anatoly Kishinevski