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'[TECH]: What is involved in making a selectable cy'
2008\12\29@192658 by Michael Algernon

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What is involved in making a internal combustion ( gasoline or  
diesel ) engine with '"n" cylinders operate on "n" divided by two  
cylinders ?  Does one just turn off the injectors ? Are there other  
requirements ?  Does one vary the cylinder usage to reduce noise and  
wear ?  Can a DIY meddler attempt such a project on a 1997 8 cylinder  
gasoline fueled SUV ?  What are the fuel saving ramifications ?  
Ideally I would like to drive around on "4" cylinders and switch to  
"8" cylinders to pull a trailer.
MA

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2008\12\30@093533 by M.L.

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First of all, don't do it if you rely on the vehicle..
I think you can just disconnect the fuel injectors on one bank of
cylinders (one group of 4 adjacent)
This is done for thermal reasons I believe. Cadillac has been doing
this for a long time. The issue is that you don't save 50% of fuel
because the pistons are always going up and down, and that's a lot of
friction. If I had a big old V8 to try this on, I would. I'd be very
interested to see what your results are.
I think I would put 4 DPDT relays one on each of the 4 injectors (normally ON)
Start the engine, and see what happens as I sequentially turn off the
4 injectors. The ECU will probably go crazy, don't you think?

-
ML


On Mon, Dec 29, 2008 at 7:26 PM, Michael Algernon <spam_OUTpicTakeThisOuTspamnope9.com> wrote:
{Quote hidden}

> -

2008\12\30@112122 by M.L.

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On Tue, Dec 30, 2008 at 10:24 AM, Carl Denk <.....cdenkKILLspamspam@spam@alltel.net> wrote:
> Back around 1980, Ford Cleveland Engine plant that made the 302 C.I. D.
> (5.0) 1955- 1996 (now makes the 2.5L 4 OHC V-6), as a demonstration what
> could be done with the cast iron V-8, to try and sell to management what
> the plant could do at very little extra setup costs, made several inline
> 4 cylinders. Some of the issues were:
>     Firing order of the cylinders so you got even power pulses. To
> change one needs a custom camshaft, it's not just moving sparkplug and
> injector wires around.
>

Turning off a bank of 4 cylinders in a V8 wouldn't (I think!) cause
vibration issues because the other bank should be firing like a 4
cylinder. If you wanted to cut off 3 cylinders I could see it running
roughly.
Of course though if you're just looking to save energy you could buy
an old used compact car. DIY [arguably] never makes monetary sense.

-
ML

2008\12\30@150022 by Michael Algernon

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>
> On Dec 30, 2008, at 7:03 AM, M.L. wrote:
>
> First of all, don't do it if you rely on the vehicle..
> I think you can just disconnect the fuel injectors on one bank of
> cylinders (one group of 4 adjacent)
> This is done for thermal reasons I believe. Cadillac has been doing
> this for a long time. The issue is that you don't save 50% of fuel
> because the pistons are always going up and down, and that's a lot of
> friction. If I had a big old V8 to try this on, I would. I'd be very
> interested to see what your results are.
> I think I would put 4 DPDT relays one on each of the 4 injectors  
> (normally ON)
> Start the engine, and see what happens as I sequentially turn off the
> 4 injectors. The ECU will probably go crazy, don't you think?
thanks for reminding me about the ECU .....  The ECU will probably  
blow a gasket mentally.
So what one really requires is qty two 4 cylinder engines which take  
turns running or both run for more power or charge a battery that  
drives a superconductor electric motor to feed squirrels running  
inside a waterwheel that pump water to.........................
MA

{Quote hidden}

2008\12\31@002220 by Herbert Graf

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On Mon, 2008-12-29 at 17:26 -0700, Michael Algernon wrote:
> What is involved in making a internal combustion ( gasoline or  
> diesel ) engine with '"n" cylinders operate on "n" divided by two  
> cylinders ?  Does one just turn off the injectors ? Are there other  
> requirements ?  Does one vary the cylinder usage to reduce noise and  
> wear ?  Can a DIY meddler attempt such a project on a 1997 8 cylinder  
> gasoline fueled SUV ?  What are the fuel saving ramifications ?  
> Ideally I would like to drive around on "4" cylinders and switch to  
> "8" cylinders to pull a trailer.
> MA

>From a mechanical perspective it's quite doable, as long as you choose
the correct 4 cylinders your V8 will run pretty much as smoothly running
on 4 vs. 8.

A major problem however is the ECU. With only 4 cylinders burning fuel
the ECU will detect a lean condition (higher O2 in the exhaust flow).
Assuming the lean isn't outside it's control parameters (which will
cause it to go to open loop, throw a code, and likely result in the
engine stalling, although there's a chance it might limp along) the ECU
will increase the amount of fuel injected. Depending on the ECU this
will at best result in a rich condition that just wastes fuel. Next best
is the engine will just stall. The worst is the engine will keep
running, but running so rich it will eventually foul the oil (possibly
resulting in a seized engine), while dumping so much unburned fuel into
the cats causing fouling of the O2 sensors and pretty much cutting the
remaining life of the cat(s) to zero.

So, is it doable? Technically? Yes, I think it's possible to get it
burning less fuel (certainly not 50%, figures I've seen of trucks that
have this system report a drop in fuel usage on the highway from
16L/100km to 13L/100km), if you twiddle enough. Engine life will likely
be degraded though. Financially, it's not worth the effort IMHO.

TTYL


'[TECH]: What is involved in making a selectable cy'
2009\01\02@102257 by Howard Winter
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Michael,

On Mon, 29 Dec 2008 17:26:34 -0700, Michael Algernon wrote:

> What is involved in making a internal combustion ( gasoline or  
> diesel ) engine with '"n" cylinders operate on "n" divided by two  
> cylinders ?  Does one just turn off the injectors ? Are there other  
> requirements ?  Does one vary the cylinder usage to reduce noise and  
> wear ?  Can a DIY meddler attempt such a project on a 1997 8 cylinder  
> gasoline fueled SUV ?  What are the fuel saving ramifications ?  
> Ideally I would like to drive around on "4" cylinders and switch to  
> "8" cylinders to pull a trailer.

Having (say) a V8 running on 4 cylinders doesn't make economical sense, because you'll need the same energy from the 4 cylinders to achive the performance your
right foot is demanding, and the 4 non-running cylinders will be wasting energy as air pumps - all the suck-squeeze-nobang-blow energy would be wasted.  Added
to which you're pumping slightly warmed air into the exhaust system, which would upset the electronics trying to set the mixture, and may cool down the catalytic
converters to a non-working temperature.  If you had a completely separate exhaust system for each half you could hold open all the exhaust valves on the
non-running cylinders to minimise the pumping loss, but it's still not zero.  But I still thing the only time you'd be saving fuel would be while idling in traffic.

Also, while diesel engines inject direct into the cylinders petrol injection sometimes (usually?  always?) injects into the inlet manifold, so you can't just stop a
particular injector and expect that to exactly starve one cylinder  - remaining fuel vapour in the manifold could result in a very weak mixture entering the cylinder,
with possibly detonating results - or unburnt fuel passing out into the exhaust.

When I was a kid I roughed-out a design for a 4+2 cylinder inline engine, with a clutch between the halves so that one half could be disconnected and stop, and it
had electromagnets to synchronise the two so that it was balanced in the combined configuration, but I'm still not convinced it would have made economic sense.  
The Prius idea of stopping the engine when it's not needed, and having instant-start when it is needed would probably result in better fuel saving than any crafty
engine-size tweaking.

Cheers,


Howard Winter
St.Albans, England


2009\01\02@125937 by Tobias Gogolin

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I heard people inventing things like this with electric valving, It would
also cut on losses due to compression and decompression, and theoretical one
could change the motor to be a compressor for energy storage during braking,
then use the compressed air by changing the valving to be a compressed air
motor...

Anyhow I rather recommend investigating electric conversions...


On Fri, Jan 2, 2009 at 7:22 AM, Howard Winter <.....HDRWKILLspamspam.....h2org.demon.co.uk>wrote:

{Quote hidden}

> -

2009\01\02@135405 by M.L.

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On Fri, Jan 2, 2009 at 12:58 PM, Tobias Gogolin <EraseMEusertogospam_OUTspamTakeThisOuTgmail.com> wrote:

> Anyhow I rather recommend investigating electric conversions...

Or hybrid conversions:

http://utahelectriccars.com/
http://www.go-ev.com/EMIS.html

-
ML

2009\01\02@152845 by apptech

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> Having (say) a V8 running on 4 cylinders doesn't make economical sense,
> because you'll need the same energy from the 4 cylinders to achive the
> performance your
> right foot is demanding, and the 4 non-running cylinders will be wasting
> energy as air pumps - all the suck-squeeze-nobang-blow energy would be
> wasted.

AFAIR the folks who do this turn off the "cams" on the dead cyliners so that
they act as air springs.


  Russell

2009\01\03@101719 by Sean Breheny

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Hi Howard,

I believe you are correct about injecting into the intake manifold BUT
I was under the impression that the injector timing still mattered so
that must mean that the fuel/air mix is sucked into the cylinder very
fast, so it may still be specific to each particular cylinder.

Sean


On Fri, Jan 2, 2009 at 10:22 AM, Howard Winter <HDRWspamspam_OUTh2org.demon.co.uk> wrote:
> Also, while diesel engines inject direct into the cylinders petrol injection sometimes (usually?  always?) injects into the inlet manifold, so you can't just stop a
> particular injector and expect that to exactly starve one cylinder  - remaining fuel vapour in the manifold could result in a very weak mixture entering the cylinder,
> with possibly detonating results - or unburnt fuel passing out into the exhaust.

2009\01\03@115730 by Herbert Graf

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On Fri, 2009-01-02 at 15:22 +0000, Howard Winter wrote:
> Having (say) a V8 running on 4 cylinders doesn't make economical sense, because you'll need the same energy from the 4 cylinders to achive the performance your
> right foot is demanding, and the 4 non-running cylinders will be wasting energy as air pumps - all the suck-squeeze-nobang-blow energy would be wasted.  Added
> to which you're pumping slightly warmed air into the exhaust system, which would upset the electronics trying to set the mixture, and may cool down the catalytic
> converters to a non-working temperature.  If you had a completely separate exhaust system for each half you could hold open all the exhaust valves on the
> non-running cylinders to minimise the pumping loss, but it's still not zero.  But I still thing the only time you'd be saving fuel would be while idling in traffic.

FWIW, "shutting off half the cylinders" is done with some engines, and
works. The Dodge Hemi (5.7L) comes in a version that can shut off half
the cylinders when not needed. There are various names for this
technology:

en.wikipedia.org/wiki/Variable_displacement
en.wikipedia.org/wiki/Multi-Displacement_System
en.wikipedia.org/wiki/Variable_Cylinder_Management
http://en.wikipedia.org/wiki/Active_Fuel_Management

The technology DOES work. However, the fuel savings are no where near as
good as some hope for. I've seen numbers between 5 and 20% savings.
Doesn't sound like much, but considering we're talking about some
engines that normally consume 14-16L/100km on the highway, this can be a
substantial savings over a fleet.

A friend of mine has a car with MDS. His usage on the highway goes from
16L/100km to about 13L/100km (MDS has the most effect on light load
driving, i.e. cruising on the highway).  TTYL

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