cylinder deactivation - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 28 (permalink) Old 08-24-2008, 05:59 PM Thread Starter
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cylinder deactivation

I was wondering if it would be possable for us to deactivate two cylinders on our trucks for extra fuel ecomomy. It would be as simple as unplugging two injectors(or putting them on a toggle switch). I know this would make the truck run a bit rough. I was wondering if it would actually help much because the cylinder would still compress air, but make zero power. I guess in the long run it would be a bad idea because of the vibrations caused by a rough running engine, seems like it would be bad for the main bearings in the engine. Any thoughts??
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post #2 of 28 (permalink) Old 08-24-2008, 07:41 PM
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Re: cylinder deactivation

Baddd idea. Having bad injectors I know exactly how this one plays out. Yes it makes it run bad but it gets horrible the first hill you run across skip wise and there are times it wont crank with even one injector not firing. Usually the motor has to be completely cold for it not to start from just one injector but it happens. Been there done that, way to often.

The only way to pull off better economy from cutting out injectors would be where the computer did it on its own and under certain conditions. The systems used on modern cars that do this cut them out at certain times, at no time does it just turn off so many cylinders continously.

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post #3 of 28 (permalink) Old 08-24-2008, 09:59 PM
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Re: cylinder deactivation

I think he meens he would have a switch.....SO for starting and hills and towing he would run all 8, but on long straight trips switch off 2 and run 6........


However this would throw the PCM into a chitfit.....And by turning the other two "dead" holes into a big compressor would act more like an engine break and cause worse mileage IMHO

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post #4 of 28 (permalink) Old 08-24-2008, 10:42 PM
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Re: cylinder deactivation

Cylinder deactivation is just gas-engine thinking being imposed on diesels. A big diesel, under light load, simply reduces the amount of fuel injected.

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post #5 of 28 (permalink) Old 08-25-2008, 01:05 AM
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Re: cylinder deactivation

When they de-activate cylinders in gasoline engines they don't just shut off the fuel, they have to let the compression out or you get extra drag from compressing dead air.

Also they still turn on those cylinders every 5-10 minutes. They have to keep the cylinder up to temp for when you suddenly want all 8 on.

It's not do-able (reliably) on a 7.3, or really any of the current diesels.

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post #6 of 28 (permalink) Old 08-25-2008, 11:59 AM
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Re: cylinder deactivation

Quote:
Originally Posted by Dave Whitmer View Post
Cylinder deactivation is just gas-engine thinking being imposed on diesels. A big diesel, under light load, simply reduces the amount of fuel injected.
So you don't think a V-6 Power Stroke would get better mpg than the V-8 7.3? (non-loaded, freeway driving)
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post #7 of 28 (permalink) Old 08-25-2008, 02:31 PM
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Re: cylinder deactivation

There is a mechanism on the Caddy's with cylinder deactivation that just holds the exhaust valves open on the dead cyinders, so they just pump free. I believe it it oil pressure that actuates it.

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post #8 of 28 (permalink) Old 08-25-2008, 02:34 PM
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Re: cylinder deactivation

Great thinking but disadvantages have been stated.

Biggest deal is the electronic valves, no camshaft, that can tune the cam profile on the fly, and float the valves for no compression on dead cylinders.

Iirc the corvette needs 60hp to maintain 65mph. In some testing they could shut half the motor off, but it's a race car not a fuel sipper and it just did not sound cool with a v4 running.

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post #9 of 28 (permalink) Old 08-25-2008, 08:53 PM
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Re: cylinder deactivation

The Cadillac Modulated Displacement motors used in '81 used electronic solenoid actuated mechanisms to alter the fulcrum point of the rocker arms for the Intake and exhaust valves on 4 of the 8 cylinders of the 6.0 motors. They did not use the electronic/oil lifter gizmos like they have today, things were much simpler then.
The idea is to keep the valves closed to retain the heat within the cylinders. You do not want the valves open, they must stay closed, so it's not as simple as just 'turning off' a couple of injectors. The Modulated Displacement system allowed the rockers to 'unseat' from their fulcrum preventing them from opening the valves. The modern systems use a spring in the lifter controlled by oil pressure to do the same thing. The Cadillac V8-6-4 motors, as they became known, had more issues than successes, due mostly to poor electronics for the time. The concept was, basically, ahead of it's time. The solenoid/mechanics hardware was quite simple and reliable, but the electronics were not. A lot has changed in the electronics community over the past 28 years.

You might be able to tell that this has been a pet project of mine for quite some time, I just need the time to follow up with it.
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post #10 of 28 (permalink) Old 08-27-2008, 12:50 AM
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Re: cylinder deactivation

It all depends on how you arrive at a “V-6 PowerStroke.”

If you manufactured a “Powerstroke”engine with only six cylinders, it might get a little better MPG at a given road load because of reduced engine friction.

If you manufactured an 8 cylinder PowerStroke engine that occasionally deactivated two cylinders the engine friction torque would remain exactly the same whether six or eight cylinders were activated, therefore the fuel consumption would remain the same.

This is IMO, an idle discussion because deactivation of cylinders is an issues that have to be addressed by manufaturers. With ULSD, Tier II, and the California diesel ban in place, I doubt we’ll see any new diesels

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