Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - 10-15% reduced consumption after "engine split" (physically deactivating 2 of 4 cyl.)

JohnAh · 08-13-2012, 06:50 AM

I guess there are two reasons that an "engine split" will increase fuel efficiency:

Friction losses are reduced when the piston, conrod and valve mechanism is nearly halved. (crankshaft/camshaft bearings are still the same and so is the oil/water pumps) I noticed a huge difference in engine breaking after my "engine split", it almost felt as if I hade put the gears in neutral when I released the throttle.

Even if the reduction in friction losses most likely make a noticabce difference I think more of the improvement comes from the fact that combustion will be more efficient when the cylinder filling/compression is almost doubbled.

An interesting test would be to only disconnect the valves of two cylinders. On a push-rod engine (unlike the Fiat 127 i modified) this may be done very easy by removing the push-rods and/or the adjustment screws for the corresponding rocker arms. The sparkplugs should be left in place with their cables still connected. The cylinder pressure should even out and hopefully there will be no build-up of engine oil above the pistons...
Such a test should show how much of the 10-15% saved fuel is because of the reduced frictions or de improved combustion. This modification would be non destructive and reversible, but also keep the engina balance normal.

The possible problems I see by only disconnecting the valves of two cylinders is what happens to the engine oil on the cylinder walls and how to take care of the rattling cam lifters that may be difficult to remove on some engine designs without ripping appart the entire engine or at least the cylinder head.

08-13-2012, 06:50 AM	#23 (permalink)
JohnAh EcoModding Apprentice Join Date: May 2012 Location: Vallentuna, Sweden Posts: 129 Phantom Blot (Spökplumpen in swedish) - '75 Saab 96 V4 90 day: 52.77 mpg (US) Thanks: 17 Thanked 55 Times in 30 Posts	I guess there are two reasons that an "engine split" will increase fuel efficiency: Friction losses are reduced when the piston, conrod and valve mechanism is nearly halved. (crankshaft/camshaft bearings are still the same and so is the oil/water pumps) I noticed a huge difference in engine breaking after my "engine split", it almost felt as if I hade put the gears in neutral when I released the throttle. Even if the reduction in friction losses most likely make a noticabce difference I think more of the improvement comes from the fact that combustion will be more efficient when the cylinder filling/compression is almost doubbled. An interesting test would be to only disconnect the valves of two cylinders. On a push-rod engine (unlike the Fiat 127 i modified) this may be done very easy by removing the push-rods and/or the adjustment screws for the corresponding rocker arms. The sparkplugs should be left in place with their cables still connected. The cylinder pressure should even out and hopefully there will be no build-up of engine oil above the pistons... Such a test should show how much of the 10-15% saved fuel is because of the reduced frictions or de improved combustion. This modification would be non destructive and reversible, but also keep the engina balance normal. The possible problems I see by only disconnecting the valves of two cylinders is what happens to the engine oil on the cylinder walls and how to take care of the rattling cam lifters that may be difficult to remove on some engine designs without ripping appart the entire engine or at least the cylinder head.