Old question. Sorry to beat a dead horse... (DIY cylinder deactivation)

[ksa8907]

I'm thinking out loud here, what if you leave the exhaust valve closed and remove the intake valve. Obviously disconnect the injector and spark plug.

After thinking about this you would actually have forced induction on the cylinders that you leave operable since every revolution would draw air in and immediately push it back to the intake.

[Frank Lee]

All that stuff reversing directions and whooshing around is sure to be a net loss.

[t vago]

+1

Effective cylinder deactivation needs to disallow any mass flow at all through the combustion chamber. This means that both intake and exhaust valves remain disabled for the deactivated cylinders. Otherwise, you're just adding more make-work for the engine.

[redpoint5]

Great explanation Frank!

I wonder what extra precautions, if any, are required to make engines with cylinder deactivation reliable? With the same cylinders deactivating and shifting a higher load to the remaining ones, I would expect those to wear out faster. Is there any evidence of the active cylinders wearing out at faster rates than the others?

I bring this up because I get a full Blackstone oil report every year when I change the oil on my TSX. Every year it shows slightly higher than average iron wear, suggesting I might be wearing my engine out a little faster than most. My best guess as to why this would happen is that I tend to shift early and place a larger load on the motor when accelerating. I'll go to 85-90% load on every acceleration event including infrequent pulse and gliding.

[user removed]

I think deactivation will be a tough sell in a 4 cylinder engine, taller tires or lower overall gearing is a better tactic. On vehicles with hugely oversized engines, cylinder deactivation will be more significant efficiency wise (which is indicitave of their poor design). Not interested in arguments but you are still accelerating and decelerating the mass of the piston and a portion of the con rod, on the dead cylinder ('s). While an "air spring" may reduce that loss, I'm more inclined to think that adds work and inertia may even overpower compression as far as loss percentages.

regards
Mech

[Cobb]

I wonder how use of different octane fuel effects this? How about warm vs cai?

One of the way guys pull off these big mpg numbers is to milk lean burn or what ever system the vehicle has in a pulse and glide situation. So lets say you can enter this 4 cylinder mode at 70mph and maintain it as you slowly slow down to 60, then charge back to 70 mph and repeat.

Basically a pulse n glide, but instead of turning the engine of and shifting to neutral you just work the throttle to enter the 4 cylinder mode and hold it til you reach the bottom speed of your glide.

Originally Posted by pgfpro

I have cylinder deactivation on my 2013 GMC Sierra Z71.
Instant readings 18 mpg disable, and 24 mpg enable.

I wish GM would of made it more usable in a broader range then they did. It's only comes in at very very light load. When activated it does help with fuel mileage. I could see it working great in areas where the terrain is very flat.

[Frank Lee]

Originally Posted by redpoint5

Great explanation Frank!

I wonder what extra precautions, if any, are required to make engines with cylinder deactivation reliable? With the same cylinders deactivating and shifting a higher load to the remaining ones, I would expect those to wear out faster. Is there any evidence of the active cylinders wearing out at faster rates than the others?

Thanks, I hope I got it all right; some aspects of it seem counter-intuitive, like why does the throttle need to open further when cylinders are shut down and the vehicle is only demanding the same power output.

I read somewhere- I think it was regarding the Honda deac system- that they don't expect any wear differences between dead and live cylinders. I find that suspicious at best, but maybe what they are really saying is whatever differences there may be are insignificant enough to ignore, and not make provision for alternating the cylinders' duty cycles. That could very well be as cylinder/piston/ring wear is not at all what it used to be; in the old days hardly anyone got 100,000 miles out of their car and now if you pull a cylinder head off a 150,000 mile car the cylinders look just as fresh as the day they left the factory.

[MetroMPG]

Originally Posted by Frank Lee

I read somewhere- I think it was regarding the Honda deac system- that they don't expect any wear differences between dead and live cylinders. .

Ironically, Honda just settled a class action lawsuit related to their 6 cylinder engines equipped with cylinder deactivation:

Honda has agreed to settle a class-action lawsuit over claims that it manufactured 1,593,755 defective vehicles that excessively burn oil and require frequent spark plug replacements.

The settlement concerns all U.S. 2008-12 Accord, 2008-13 Odyssey, 2009-13 Pilot, 2010-11 Accord Crosstour and 2012 Crosstour vehicles equipped with six-cylinder engines that have variable cylinder management.

http://www.autonews.com/article/2013...-burning-claim

It doesn't say what in the feature's design led to the oil consumption problem.

[user removed]

Piston rings have a taper on the top of the ring that is supposed to direct some of the force from combustion pressure to push the rings outward. Without combustion pressure the rings will not exert the force needed to control oil flow past the rings.

regards
mech

[Frank Lee]

That's only for the top ring and only for compression; second ring and oil rings scrape to control oil.

P.S. The thing to find out would be if all six are fouling out or just the three that deac.