Cylinder de-activation. will it work?

[Daan]

Would weather/temperature conditions have an overall effect on the calculations as well - do we get slightly better mpg on very cold days due to the denser air??

Yes, it does have an effect, but not in the direction you think: you will use more fuel because the aerodynamics are less favourable because the air is denser. Thats why you use more fuel during the winter.

daan

[vulcan bomber]

Cold weather puts more in your fuel tank as well when you fill up as well. And due to colder intake temps, burns the fuel more efficiantly.. Its swings and roundabouts with the weather.

[Daan]

Its swings and roundabouts with the weather.

If only it was:

http://www.metrompg.com/posts/winter-mpg.htm

Daan

[zoltan]

We get much more power on the dyno on a typical crisp cold winters morning when there is a high pressure system over us. Even despite correcting the figures to ISO, engines still perform much better in it. That said, on an engine dyno it is only breathing in the good cold air and not running through it

[Tanuki]

Commercial cylinder-shut-down systems do it by closing both intake and exhaust-valves. They generally arrange for the cylinder to get a full 'suck' of intake-air and then shutting both valves - the piston then compresses the air and allows the air to push the piston back down (working like an air-spring).

This 'cushions' the process and damps-down the harshness that would otherwise come from 'misfiring' a cylinder.

They also generally switch the 'shut-down' cylinders around after a few cycles - so if it's shut-down 1 and 3 for a couple of engine-revolutions it will then bring those cylinders back in and instead shut down 2 and 4 for a few cycles. This stops some cylinders getting hotter/cooler than others - something which would be a potential problem when you stomp the throttle and need all cylinders to suddenly pull their full weight.

--Tanuki.

[Yostumpy]

Would weather/temperature conditions have an overall effect on the calculations as well - do we get slightly better mpg on very cold days due to the denser air?

Surely the only way to make a serious dent in economy is to reduce weight and wind resistance. Maybe lower the springs, a smooth steering guard to improve airflow under the front, road biased tyres. Then remove the roof and sides, recline the seats, fold the screen down and wear a swimming cap.

I get much better milage when its v.warm weather. like it was the last few weeks.

My old truck was a 2.5n/a and I put one of those perforated steering guard jobbies on and that knocked it for about 1.5mpg from day 1

Have lowered the rear springs, taken off the Britpart DA4208 and fitted ANR3450, gen LR wolf springs, and its droppd the rear 30mm

[Daan]

Yes I could fit an overdrive @ £1200, or change the t/box for 1.22 or even the v8 one, but I'm trying all I can without spending much, as yes it would be loverly to have a rocky mountain overdrive, but I couldn't justify the expense for, say 6-8mpg gain.

.

Has yours got the 1.6 box?

I reckon the change to a 1.0 box, which you probably can do for les than £100 pounds, that is the biggest hit you will ever give to your consumption. If I needed my landrover for daily driving, that would be my number 1 mod. In fact, I am considering it at the moment for mine, but it probably is not worth it for my mileage.

Daan

[elbekko]

Do you really think it's viable to have a 1.0 box with a TDi? It already feels fairly sluggish with a 1.2, so I can't imagine having to push the engine harder on acceleration will save fuel.

Really what you want is an overdrive, so acceleration is unaffected, but you have an extra gear on the motorway. Too bad they're all so damn expensive.

[simonr]

If it will genuinely give an improvement of 6 to 8mpg - then, based on 10,000 miles per year, it will save you about £600 per year. On that basis, they are pretty good value!

Why don't you pump your tyres up to the max, fit pizza trays to the wheels (to make the outside of the wheel flat, which apparently makes a reasonable difference) then every time you fill up, put 20% of the cost into your piggy bank. At the end of the year, you'll be able to buy an Overdrive!

Si

[HoSS]

I'm having visions of a Concorde style visor that slides up and improves the front aerodynamics at cruising speed

Go on, someone do it please - Concrover

[Daan]

Do you really think it's viable to have a 1.0 box with a TDi? It already feels fairly sluggish with a 1.2, so I can't imagine having to push the engine harder on acceleration will save fuel.

Really what you want is an overdrive, so acceleration is unaffected, but you have an extra gear on the motorway. Too bad they're all so damn expensive.

If the objective is to save fuel, absolutely. The fact that it will be slow on acceleration shouldn't matter, because that is the way you should be driving anyway. To be fair though, it will only matter in 1st gear, from then on, your shiftpoints can stay at the same RPM, it just happens at a higher speed. And probably use 5th as an overdrive. If it proves too tall, you can fit 205 tyres, narrower and lower, and will save even more.

Daan

[elbekko]

The fact that it will be slow on acceleration shouldn't matter, because that is the way you should be driving anyway.

To save fuel, perhaps. But not to be a safe driver. My TDi with 1.2 TC is just barely adequate for safely merging on a motorway, and I usually feel as if I'm stressing it when cold. I don't think you'll still care about a bit of fuel savings if a big truck hits you in the arse.

[ian_s]

i've been thinking about this over the last few days, and the more i think about it the more it seems to me like if you could safely divert the injector pulses, this could work.

i would deactivate the inner 2 cylinders. if you did the outer 2, they will cool down more while they are deactivated and so when they are reactivated, they would be less efficient for a while. deactivating the inner two means the outer two will help to maintain heat in the middle of the block.

the actual deactivation i think could be done with just a single solenoid on each injector pipe, fitted via a t-piece to act as a pressure relief valve. they would have to be able to withstand the pressures provided by the IP during normal running, but when opened would provide an alternative path, offering almost zero resistance and so not allowing the pressure to build high enough to open the injectors. you would then divert the fuel back to the fuel tank, but the pipe work would have to be able to withstand the pulses.

i think the whole system would benefit from being electronically controlled, so it only deactivates the cylinders when conditions are right:

1) engine at normal temperature

2) revs above set figure e.g 1200 rpm

3) throttle position below 50%

this *might* just work. i think though that the resulting 2 cylinder engine with 2 cylinders of dead weight would be quite difficult to live with.

as for whether it would improve your fuel consumption, i have no idea. As Simon said, you still need the same amount of power to be produced, so the real question is can 2 harder working cylinders produce the same amount of power for less fuel than 4 cylinders?

[FridgeFreezer]

For less money & better effect surely you could just swap in a more efficient engine? Perhaps even a modern one... with cylinder shutdown?

[Escape]

To save fuel, perhaps. But not to be a safe driver. My TDi with 1.2 TC is just barely adequate for safely merging on a motorway, and I usually feel as if I'm stressing it when cold. I don't think you'll still care about a bit of fuel savings if a big truck hits you in the arse.

As long as the truck stays there, you should get great MPG!

Back on topic, I know Lotus experimented with shutting down 2 cilinders on the 910S 4-cil engine. On low rpm and load, the ECU would alternate firing injectors 1/3 and 2/4, making it in effect an 8-stroke engine. It did run a bit rough, no idea how much fuel it saved, no idea why anyone would care in Lotus either...

[zoltan]

Lotus did lots of curious research projects including some interesting work on solenoid powered poppet valves to get very accurate control of valve timing events

[Yostumpy]

Overdrives! yes. Now if a 1.2 t/box in a tdi makes it sluggish, this is only a 16% increase IIRC, but the o/d is 28%

Now I normally drive between 55-57mph on t'open rood. For 2 reasons, well 3 actually,

I like it at that speed, as I don't get caught up in t'traffic rushin'about

The engine sounds unstressed and buzzes along nicely (the most fuel efficent speed is usually that just after top gear is engaged)

Its a good speed, as any faster , the law of diminishing returns re the air pressure on the front.

Now say with a 1.2 t/box on a tdi, what speed would you travel at?

a) at 55mph..... so as to make least impact into the wind, BUT it would be like driving your std t/box around @45mpg in 5th, a tad overgeared at this speed for inclines etc

b) 60-65, which in effect means the engine is working harder than it was at 55 with the old t/box on, as its pushing x tons more air out of the way to run at an efficient rev range.

How would an overdrive on a 1.6 box pan out. you'd have crawler range in high range, and overdrive range which would be somewhere between 1.4 &1.2?

[TheRecklessEngineer]

IIRC my thermodynamics, a diesel reaches peak efficiency at around 80-85% load. So you really want it geared to be at such an rpm as to correspond with 80% maximum fuel at your cruising speed (58mph from the above statement).

If of course that co-incides with a reasonable boost level from the turbo. If it's in an area of no boost then the whole thing goes out the window as your turbo will be a hinderance rather than a help.

This will of make the whole thing feel very sluggish as the engine will only have another 20% left to give. That means you'll have to drop down a gear or two for inclines.

Fit a CVT?

[tacr2man]

By the time you have messed your landy about doing all this , you might as well get a Picanto this will give you a 200% increase in fuel economy , cheaper tyres etc etc . JMHO

[Daan]

I dont know what revs you are seeing at these speeds, but most super efficient cars (like vw bluemotion etc) are seeing about 2000 rpm at 70 mph. So I think that is what you should look at aiming for. Also, with regards to aerodynamics: Most mods tend to be done at the front, but from what I learned, the most drag is created at the rear, pulling the back out of a vacuum. So it might be worth thinking about that end as well.

Daan

[Yostumpy]

its all just a bit of fun really, Ok, its a landrover, but if you CAN get 30mpg running about instead of 25mpg, then why not. Its still a landy, still goes off road, and still makes me smile!

2000rpm@70! Imagine the tonnage of air pressure on a landy at 70 as opposed to 55mph!, that would mean about 1200 rpm at 55mph, well too slow.

[Yostumpy]

By the time you have messed your landy about doing all this , you might as well get a Picanto this will give you a 200% increase in fuel economy , cheaper tyres etc etc . JMHO

Don't wanta Picanto, want my Wallace!!!!!!!!!!!!!!!!!!!!

[Daan]

its all just a bit of fun really, Ok, its a landrover, but if you CAN get 30mpg running about instead of 25mpg, then why not. Its still a landy, still goes off road, and still makes me smile!

2000rpm@70! Imagine the tonnage of air pressure on a landy at 70 as opposed to 55mph!, that would mean about 1200 rpm at 55mph, well too slow.

I mean you should aim for roughly 2000 rpm at your cruising speed, for best economy.

Daan

[simonr]

IIRC my thermodynamics, a diesel reaches peak efficiency at around 80-85% load. So you really want it geared to be at such an rpm as to correspond with 80% maximum fuel at your cruising speed (58mph from the above statement).

I may be wrong, but IIRC it's 80% of the max torque at a given RPM, but the efficiency also reduces as the rpm increases. Therefore, it's not simply a case of increasing the ratio, it's getting the ratio right for the kinds of speeds you want to cruise at. So, perhaps 50 in 4th and 70 in 5th. The RPM wants to be as low as possible, but not exceeding 80% torque.

Si

[Yostumpy]

ok then! who's got a rev counter, on a std def t/box set up, and who can tell me the approx rpm at 50 55 60? be very grateful to know what i'm turning when doing 55 (on the clock that is) Ta muchely