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Old 02-08-2008, 10:17 PM   #1 (permalink)
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Cylinder deactivation discussion

i missed the title, this more like cylinder decommissioning

ive always wondered if i take half the pistons,rods and valvetrain out of an engine will it get better mileage? or will the remaining cylinders use more gas working twice as hard?

yes & no or no & yes ?


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Old 02-08-2008, 10:28 PM   #2 (permalink)
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^YES and no!

It has been done before. I've seen where some college kids back in the day pulled 2 cyls. out of a VW Bug and coaxed 58 mpg out of it, IIRC.
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Old 02-09-2008, 12:54 AM   #3 (permalink)
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2 Points

diesel_john: 2nd point -- I kinda have some experience with cylinder deactivation. A couple years back, I deactivated 2-cylinders in the 'Teg and ran it 50 miles. Too bad it shook too much and the O2 sensor dumped more fuel in the operating cylinders.

If you make a 2-cylinder from a 4 (or 3-cylinder from a 6), you'd have to pull the whole connecting rod and cylinder with the top-end components from the opposing cylinders. Now you have a huge hole in the cylinder top where oil can splatter out. If you can seal it up and balance it out, then you may have a winner -- providing the cylinder action is balanced. Next you'd have to tell the ECU to expect half the burned fuel for stoich. I've heard that it's possible, and has been done.

On a side note: I've driven the new Chevy Impala 3.9L with the 3-cylinder mode (of 6) and the SS with 4-banger of 8. LOD, RPM, and speed determined activation and deactivation with the ECU -- a 5% FE savings was a REAL stretch. I'd like to force the whole thing to work in half-mode all the time. I'm sure it could be hacked. Chrysler's HEMI has a similar system. Extra weight, I s'pose, but half power should result in a big increase if driving properly.

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Old 02-09-2008, 01:20 AM   #4 (permalink)
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"Now you have a huge hole in the cylinder top where oil can splatter out."

Valves closed and a dummy spark plug, where's it gonna go?

The problem area is on the crank throw- should a stationary or rotating cover be affixed and how? And doesn't the ECU already know how much fuel to send via the remaining injectors and O2 sensor?
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Old 02-09-2008, 02:16 AM   #5 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
"Now you have a huge hole in the cylinder top where oil can splatter out."

Valves closed and a dummy spark plug, where's it gonna go?

The problem area is on the crank throw- should a stationary or rotating cover be affixed and how? And doesn't the ECU already know how much fuel to send via the remaining injectors and O2 sensor?
Welp, the cover is tricky bit. If you leave it untreated, you have to disable the valve action (grind the cam lobe down) or else the valve will open and leak oil. If the valves are seated firmly then there should be no problem.

I reported in my experiment that the ECU throws a CEL and a "Cylinder Misfire #1, or #3, code etc.) and dumped the fuel into the operational cylinders to acheive the proper air/fuel ratio for the oxygen sensor. In my application, the ECU didn't figure it out. YMMV, but OBD-II is fairly similar in operation in most vehicles. Pre-OBD vehicles, with carbs, have noted to defeat the system and run well.

BUT, the problem also resides in hot/cool spots with operations vs. dummy cylinder areas. Coolant has a tough time regulating bores with no combustion and hot spots with where the action is conducted.

I'm not trying to downplay the deactivation concept -- just reporting my experience and research. It can likely be defeated with proper preparation and ECU mods.

Sorry to hijack the thread -- we should get back to Atkinson action. Otherwise, maybe a cylinder deactivation thread is required? Feel free to start one, anyone. I failed at that experience, so I'm moving on...

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Old 02-09-2008, 02:43 PM   #6 (permalink)
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I wouldn't ruin the cam when all's I gotsta do is pull a few lifters (or followers as the case may be) out. Besides, the valves need to be deactivated so that the flow to the working cylinders doesn't get all screwed up, not to mention crankcase pressures. Then, later on, if I want to re-activate the cyls for some reason (experiment failed? want the power back? want to switch cyls for extended life?) nothing has been wrecked; it's a simple matter of slapping the parts back in.

You misunderstood the "cover" I mentioned, for as mentioned, it goes on the CRANKSHAFT to cover the oil hole and to provide better balance. What I have in mind is to get a few junkyard rods and cut 'em off at the big end, and bolt that onto the crank. What I'm wrestling with right now is, should they be free-spinning (depends on if they'll hit the block) or indexed and solidly bolted on? I guess I can't answer that until I have it disassembled, with parts in hand.

"BUT, the problem also resides in hot/cool spots with operations vs. dummy cylinder areas. Coolant has a tough time regulating bores with no combustion and hot spots with where the action is conducted."

I don't believe you. Neither do any of the manufacturers that offer cylinder deac from the factory.

YOUR ECU screwed up because your "deactivated" cyls were still pumping air into the exhaust stream. John and I are talking about REAL deactivation -maybe ours should be called "decommissioning"- no air being pumped, no fuel being squirted, no pistons going up and down. O2 and ECU function should be "normal" then... unless the TPS being open wider throws something askew.
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Old 02-09-2008, 03:27 PM   #7 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
[1]
You misunderstood the "cover" I mentioned, for as mentioned, it goes on the CRANKSHAFT to cover the oil hole and to provide better balance. What I have in mind is to get a few junkyard rods and cut 'em off at the big end, and bolt that onto the crank. What I'm wrestling with right now is, should they be free-spinning (depends on if they'll hit the block) or indexed and solidly bolted on? I guess I can't answer that until I have it disassembled, with parts in hand.
[2]
"BUT, the problem also resides in hot/cool spots with operations vs. dummy cylinder areas. Coolant has a tough time regulating bores with no combustion and hot spots with where the action is conducted."

I don't believe you. Neither do any of the manufacturers that offer cylinder deac from the factory.
[3]
YOUR ECU screwed up because your "deactivated" cyls were still pumping air into the exhaust stream. John and I are talking about REAL deactivation -maybe ours should be called "decommissioning"- no air being pumped, no fuel being squirted, no pistons going up and down. O2 and ECU function should be "normal" then... unless the TPS being open wider throws something askew.
[1] Why would you want the extra weight spinning on the shaft?
wouldn't that create a parasitic load or even an off balance situation?
I would opt for a small core plug or maybe drive a solid pin all the way through.

[2] You don't believe the coolant would use the empty holes as heat sinks?
I read an old manual when I was in the Army, that gave instructions and part #'s for the conversion of 4cyl jeep into 2cyl run and 2cyl pump to build an air compressor.
Very neat idea. I am sure someone in the Pentagon thought about the heating and cooling factors.

[3] No extra air means the o2 reads right.

Have fun.S.
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Old 02-09-2008, 03:44 PM   #8 (permalink)
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1. REMOVING the con rod CREATES an unbalanced condition! Now the counterweights on the crank are too heavy if there's nothing on the throw. This is an attempt to re-balance. I've read that the bottom 1/2 of the rod's weight is used for balancing cranks.

2. Absolutely I do. I don't believe it causes problems.
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Old 02-09-2008, 06:04 PM   #9 (permalink)
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A quick quote from the Chrysler info pack when the vehicle was released:

"Chrysler C300 has a four cylinder / eight cylinder engine.
Four cylinders at normal running and eight on demand.
Utilising the four cylinder demand option results in a seven percent fuel saving."

I would have thought it would be more than that.

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Old 02-09-2008, 07:23 PM   #10 (permalink)
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I wouldn't go through all the work for a measly 7%. GM boys claim up to 20%, depending on conditions. I would go through all the work for 20%. And since this way, there is no access to all cylinders at any time, I'm going to hope that there's a chance for greater than 20% improvement when it's all said and done.

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