Quote:
Originally Posted by metromizer
Thanks for posting this, I have a few comments.
only 5-10% reduction in fuel consumption just isn't enough motivation to justify the work, in my mind. By disabling a couple cylinders, but not removing the 'dead cylinder's' friction doesn't seem worth the trouble. If you leave the pistons in, you need to maintain some valve action. If you don't, the piston is compressing air needlessly. Worse, it has no place to go. Ring friction is also a big deal.
Most of the disabling a cylinder or two FE experiments I've read about, have started with a worn out and/or broken engine. I'd like to see someone test a good running engine on a dyno, then remove two pistons and run it.
Pushrod engine: there is a couple ways of dealing with loose lifters after removing pushrods, pistons, permanently disabling a couple cylinders. If you completely remove the lifter, on many engines, you must close off the lifter oiling port or replace the lifter with a plug of somesort. If you remove the camshaft, and precision grind the lobes off round, you can just leave the lifter in place. Another way to remove pistons without having to m9odify the crankshaft, is to modify the connecting rods. Saw the beam and upper end completely off, grind it smooth, and re-install what is left with bearings. That will control the oil leak from that journal. If you don't want it to turn, just add a little .003 shim stock under the bearing shells of the modified rods.
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The compression loss is actually very little, the compressed air doesn't go anywhere on the compression stroke and acts as a spring pushing back down on the piston on the expansion (combustion regularly) stroke.
The pumping losses come from actually moving air. the best bet in that case is just to remove the valve actuators (rockers, usually) and let the cylinder continue to compress and expand the air already existent.
To minimize the air in the cylinder (which will naturally dissipate over time anyway), remove the rockers while the cylinder is at TDC with either the intake or exhaust valve open.
Someone mentioned modifying the pistons by putting holes in the crowns:
While this /will/ work to reduce pumping losses, it isn't necessary as I pointed out above, because in order to do so, you would also need to prevent the valves from opening to keep oil from flowing into the manifolds from the oil mist that occurs naturally in the crankcase.
The best bet to remove friction is either to completely remove the piston from the cylinder, affecting balance in some engines, or just deal with it and move on to larger/lower fruit.
To negate (most of) the balance issue, leave the cylinders that are 180* opposed to each other. This will result in a smoother engine with a better torque curve, similar to a 180* parallel twin common in Japanese motorcycles.
It is best, I've been told, to leave the cylinders closest to each other as well in the case of 4 cylinder engines, to prevent resonant vibration as much as possible, but I'm not necessarily sure it really makes a difference.
If you really want to utilize the two cylinders you've removed, you can run pod filters on their intakes and modify their exhaust ports to feed back into the remaining two cylinders' intakes to act as a "supercharger" of sorts to maximize power for the remaining output of the engine. You would need to modify the cams by adding an additional lobe so that every down stroke were intake and every up stroke were exhaust. The result would be a compressed charge in the intake due to 2 "charge" strokes per "power" stroke of a utilized piston, and a required retuning of the fuel/ignition systems to handle that.