Idle Mind's Idea: Shut Off Injectors & Spark to Save Fuel & Engine Hour Meter

[ballpencil]

I'm sure this is an old idea and has actually been implemented. I just want to know your guys' opinion on the matter.

There's a system on some GM V8s that shuts off some cylinders on cruise speed to save fuel. Can this be implemented on 4 cylinders like 4A-GE?
I understand that GM has some mechanism to keep the valves open on the cylinders being shut off, but seeing this is impossible on 4A-GE, can we do it by simply turning off the injectors and spark for a pair of cylinders?

In order to maintain rotational balance, i believe it has to be a pair of 180 deg separated cylinders like #1 and #4.. Luckily, on a wasted spark system, the sparks are paired this way as well. As i'm using Megasquirt and EDIS-4 Wasted Spark, i can simply install a switch between the spark signal for cylinder 1&4 and injectors #1 and #4 to shut down these two cylinders anytime.

1. Will this work and actually safe fuel?
2. Would it be necessary to shut down the spark? I mean, with the injectors shut down, the sparks won't be igniting anything, just air. Is this safe for the pistons and cylinder walls?
3. I think, the reason why GM keeps the valves open is to reduce compression resistance. Some say with the valves working as normal, this would not be an effective way to safe fuel as the other cylinders will have to work harder to fight this compression resistance and consume more fuel. What do you think?

Last one, if one is to install an engine hour meter as a reference for oil change, what is the recommended interval? 300 hours?

[convertableTA23]

No idea on your no fire idea. 300hrs is too long for a car. If you take a 10,000km service interval and take into account a vehicle doing mixed run of about 30% highway and the rest stop start/city driving the average speed is approx 45km/h. Multiply that out and you end up with about 222hrs. I like to service my cars every 5,000km and for the sake of round numbers that comes in at 100hrs.

I do a bit of work on trucks, some cement trucks that do a lot of idling and low speed work. A normal prime mover is serviced every 20,000km and we drop the oil on the concrete trucks every 300-350hrs depending on what the owner/driver wants and the oil is similar to that coming out at 20,000km. Just as a reference for you.

I am guessing you would only install an hour meter because you do a lot of idle work, so yeah, I would be looking at 100hrs, 150hrs tops.

[timbosaurus]

1. No. An 8cyl with 4 de-activated needs a LOT of changes to make it run with an acceptable level of N&V (smoothness). You could barely run a 4 cyl engine in 2cyl mode.

2. Ignoring the fact it wouldn't work, I wouldn't expect leaving the plugs sparking would hurt.

3. If you leave the valves operational you are losing a lot a energy to compress air, and you don't get anything back from that by injecting fuel/making fire. By keeping valves closed (BTW, GM leaves valves closed, not open), it uses that compressed air as a 'spring' to push the piston back down, so not so much wasted energy.

[ballpencil]

1. No. An 8cyl with 4 de-activated needs a LOT of changes to make it run with an acceptable level of N&V (smoothness). You could barely run a 4 cyl engine in 2cyl mode.

it won't work even if i only deactivate in when the vehicle's coasting on long straight highway (light load)?

3. If you leave the valves operational you are losing a lot a energy to compress air, and you don't get anything back from that by injecting fuel/making fire. By keeping valves closed (BTW, GM leaves valves closed, not open), it uses that compressed air as a 'spring' to push the piston back down, so not so much wasted energy.

but by keeping the valves open, there won't be any energy wasted to compress the air in the first place?

[timbosaurus]

it won't work even if i only deactivate in when the vehicle's coasting on long straight highway (light load)?

When coasting under no load, you should turn off all fuel (decel fuel cut). When cruising under light load, as an experiment, try driving your car on 2 cylinders and see if you can cruise with that. I guarantee you will not be happy.

but by keeping the valves open, there won't be any energy wasted to compress the air in the first place?

You were talking about leaving the valves operating as normal... that is when there is wasted energy.

If you actually leave them open all the time, you'll be pushing air out the inlet... essentially backfiring and running like crap.

I guess your only other option would be to leave exhaust valve open, and inlet valve closed. Cant think of any real reason not to do that, except that it is more complicated and gives no obvious advantage over leaving them both closed.

[maccac__1590]

i still struggle to see how there systems work anyway, like if your cruising along the highway at 100 and you using xx kJ of energy to keep you moving, assuming that energy produced is directly proportional to petrol used (i realise that it wont be in all rev/load situations) then it shouldn't matter if you are running on 4 cylinders or 8, you are still gonna need the same amount of energy to keep you moving, hence fuel. unless the spring of the closed valves is enough to produce a difference, or maybe the individual cylinders are more efficient when worked harder, ie under more load. so when some are shut down and the rest are forced to work harder they are more efficient.......
i don't know im confusing myself hahah

[timbosaurus]

assuming that energy produced is directly proportional to petrol used (i realise that it wont be in all rev/load situations)

Yeah, that's the assumption that causes you confusion.

Change your thinking to "energy produced is proportional to petrol used multiplied by efficiency", and that efficency figure is lower under low-load and small throttle openings (ie: lower dynamic compression).

Then you realise that 4 cylinders working at their efficiency peak are better than 8 cylinders at low efficiency.

It's not a huge difference in reality, but every bit helps when you have 6 litres of muscle to feed

[dumbass]

the gm ecu does so much shit to get the cylinder displacement on demand to work properly
goodle "gm DOD"
it actually has one bank where the hydraulic lifters are collapsable,
then has 4 solenoids that control oil pressure to these lifters
in turn it suts down fuel and spark to that cylinder aswell
it doesnt do all cylinders at same time
there is good info out there for it and i doubt any aftermarket ecu is smart enoug to work this properly
where u dont feel and jerking when driving
if u want to save fuel fk off the toyota ecu and put decent afternarket one on there and tune it for lean fuel savings
or go buy a fking pushbike because petrol prices are going to be up the ass in 5 years

[banana_socks]

The advantage to using a V8 is that with a bank shut down you still essentially have an inline 4, and that produces power relatively smoothly. Shutting down 2 cylinders on a 4 will mean you've only got one power stroke per crank revolution. On an engine like the 4AGE with a lighter flywheel this would likely be noticeable. The other pistons will still be moving, so you'll still be harmonically balanced (unlike an actual twin) but the power delivery will be affected.

If the unused cylinders have any valves open, you'll just be uselessly pushing air around which will rob power and efficiency.
The reason it works in the GM case; the more the throttle is open the less pumping losses the engine will have. using half the engine means you've got twice the throttle (approx) and it will work more efficiently (assuming the tune isn't richer for more power)

I like that you're thinking of new ideas, but probably in the wrong direction.