cylinder shut down tech, how does a V8 run on 3 cyls?

[big_zop]

Good point and well made. I agree, until we see some tested proof, it's anyone's guess how good it really is. 20% improvement in fuel consumption is a big claim.

Yeah, i am assisting with a project that will be looking at approximately a 1% fuel saving. But the scale of the savings from that would be immense (not sure on exact figures but not able to tell anyway).

[Rcubed]

on the v6 hondas 3cyl mode shuts down one bank - 4cyl mode one cyl per bank at opposite ends. as the autospeed article says, they use removal of hydraulic pressure on lifters to prevent the valves opening [thereby removing pumping losses], and suspend fuel injection although keeping sparking.

fuel economy is improved by the same reason a 4pot will be more efficient than an 8pot all other items being the same - higher effective compression.
to create a certain amount of power an engine must injest a certain volume of air. the right amount of fuel for the conditions is added to heat the air and created pressure.
if one litre of air/rev is required; in a 2L 4 cyl the cyls will be 1/2 full in a 6L v8 the cyls will be 1/6th full. lower effective compression = lower efficiency.

to overcome this the v8 will have taller gearing to make it turn slower injesting air at slower rate but having a wider open throttle allowing higher cylinder filling. this is why a v8 dunnidoor will get 10km/L on the highway turning at 1600rpm.

[Rcubed]

the effective compression affects how quickly and completely fuel burns.
high compression = fast and more complete = less energy going out exhaust when valve opens.
the limit is detonation/pre-ignition

[Rcubed]

http://toymods.net/forums/showthread...983#post288983

[Grega]

jeez............they were trying this in the 60's if i remember rightly
funny how we seem to go round in circles...

EDIT : I have an article from GM on DOD written from some time back (about 6-12 months ago). i'll post it up here if anyone is interested?

[big_zop]

jeez............they were trying this in the 60's if i remember rightly
funny how we seem to go round in circles...

EDIT : I have an article from GM on DOD written from some time back (about 6-12 months ago). i'll post it up here if anyone is interested?

Im interested, put it up or email me if you cant.

Cheers

[timbosaurus]

Compare the fuel econony figures between the Holden VE and the Pontiac G8 to see what difference DOD/AFM/cylinder deactivation really makes.

I think it is practical proof that it works...

[wa5]

Remembering that American Gallons are different to our old
Gallon... (4 litres Vs 4.5) unless you can get the comparisson in litres / Ks ....

I have had a couple of Mazda 1300s that used to oil up one cylender .... was I ahead of my time.... did I discover "Automatic Cylender shut down" before the factories..?
note well gentle reader that both the factory and I use Oil to acheive cylender shut down...

My brother had VW powered beach buggies and he achieved the same result by bending pushrods.....

I can feel a court case comeing on..

[Grega]

ok i'll see if i can find it.

[thechuckster]

they use removal of hydraulic pressure on lifters to prevent the valves opening [thereby removing pumping losses]

weird - i would have expected the zorst and intake valves to just open a lot less and have the zorst open bore the top of a compression event - otherwise you waste power by compressing air?

[Sciflyer]

Maybe if you have half the cylinders running no compression it unbalances the engine a bit? (ie, vibration)

[allencr]

I was thinking of the rod journal being on a big eccentric that could rotated around to zero piston stroke and really take half the cyls out of action instead of dragging them around like this valve disabling BS.

Is it any surprise that most most of them put some mickeymouse gizmo in the exhaust/zorst for ear candy & moron and/or sex appeal? If I were an Engineer, I'd love the project but hate that it was being promoted & driven by salesmen, and morons with big checking accounts that want to claim that their GREEN fuel efficient car is also powerful & still sounds like ____(insert almost any phrase about sound made by a twit with sidedrafts, ITB's or Turbo muffler, highrise header, pod intake, etc.), while looking down their environmentally conscience noses at our old 1.6L performance machines.
****************
Also ZORST, a site/URL for its roots/origin? Thanks.

[MS112]

weird - i would have expected the zorst and intake valves to just open a lot less and have the zorst open bore the top of a compression event - otherwise you waste power by compressing air?

It is true that work is done due to compressing the air mixture and is lost in the form of waste heat, however think of the closed cylinder as a spring: the piston compresses the "spring" and then on the down stroke that stored energy potential is released. Thus, the net effect is, ideally, supposed to be zero.

And perhaps the energy loss due to work being done on the gas is considerably less than pumping losses?

[big_zop]

Compare the fuel econony figures between the Holden VE and the Pontiac G8 to see what difference DOD/AFM/cylinder deactivation really makes.

I think it is practical proof that it works...

This has been bugging me for a little while and i wasnt sure why. First off, what are they?

The other thing i want to question is that are the two values even valid. The fuel economy test is on two completely different cars, yes they may share the same engine but we all know that the smallest difference between engines (well, mods in our case) and ancillaries can make a big difference. There could be a difference in all the physical aspects, with the biggest contributer being weight but many unseen things like ecu tune, emission standards, fuel quality, quanitys being used and conversion factors (i saw somewhere that the old aussie gallon is different to the us gallon), actual execuction of the cylinder deactivation (remember these are tuned and calibrated here by australian engineers for our conditions) and the fuel economy test itself could be different.

It is true that work is done due to compressing the air mixture and is lost in the form of waste heat, however think of the closed cylinder as a spring: the piston compresses the "spring" and then on the down stroke that stored energy potential is released. Thus, the net effect is, ideally, supposed to be zero.

And perhaps the energy loss due to work being done on the gas is considerably less than pumping losses?

Good use of the word 'supposed' in the net effect of energy loss - as many would know that no real world application of energy conversion is perfect. Im sure that they theoretically measured the differences to determine the 'best' solution but i wonder how they would have validated their results. Being involved with a project that must prove a 1% fuel efficiency increase when there are so many factors that contribute to it (the list involved about 20 factors) then that is very hard to measure.

They all make big claims but i would love to see documented proof that its beneficial - and car manufacturers being what they are would rather go bust than reveal that kind of information (and hope that because of it they wont go bust )

The best proof i have seen of real world fuel economy increases from only one change is in the Falcon with the difference between the 6spd auto vs the 4spd auto - 10.7 vs 10.2 (BF figures with everything else the same)

[jak]

i think it would be pretty much just shutting down the injectors and probably closing the intake ports on the cylinders, while having a valve (not cam operated) a similar size to the spark plug hole placed somewhere in the cylinder head to get around the compression issue. The id say id would just pick the most even format (eg a 6cyl running on 3cyls would shut down one bank and on 4cyls would have one piston in each corner going) and then adjust the firing order so it doesnt shake around like having dropped a cylinder.

my idea anyway
Jak