Cylinder de-activation. will it work?

[Yostumpy]

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

I think this is what I was trying to say earlier, in that a disco t/box would overgear my truck for the speed I travel at, unless I speed up to 65mph, then I lose the advantage.

[western]

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

my 200tdi with a 1.410 transfer box & GKN OD gives me these figures

60mph in 5th [overdrive disengaged] 2600 rpm

60mph 5th overdrive 2100rpm

[Yostumpy]

my 200tdi with a 1.410 transfer box & GKN OD gives me these figures

60mph in 5th [overdrive disengaged] 2600 rpm

60mph 5th overdrive 2100rpm

Ah thanks for that. so at 55mph I'm turning about 2350rpm without o/d

and presumably 1950 rpm at 55mph with o/d

so one last part of the conundrum, what would the rpm be at 60mph with the disco box. Anybody?

Also can you tell what speed you engage o/d in top , I mean what speed would you drop out of it?

Also do you find it gives better mpg with o/d, or more relaxed cruising, or both? Oooo this is getting good!

[CwazyWabbit]

You want this mate, http://www.ashcroft-...ratio_calc.html and you can play with different gear boxes, transfer boxes, diffs, overdrives and tyres to your hearts content Enjoy!

[Yostumpy]

that's fun. On the strength of that , this afternoon I went trundling in the truck at 47mph to silmulate a 1.22 t/box, very quiet but sluggish as hell. Might be worth a punt if I can find a good one cheap.

[ProteuS]

Is the simplest approach to get the economy up not just to strip weight out as much as possible. Do you need to run with a spare? Perhaps just a can of tyre weld in the back. Do you need the seats in most of the time?

I seem to reall an article quite some time ago in a land rover mag where they tried to make a 50mpg defender, I think they got pretty close, by pulling the roof off, front window off, doors off (replaced with cardboard) , seats out and I think they wrapped the vehicle with a clear packing film to smooth out the surfaces.

[Yostumpy]

Is the simplest approach to get the economy up not just to strip weight out as much as possible. Do you need to run with a spare? Perhaps just a can of tyre weld in the back. Do you need the seats in most of the time?

I seem to reall an article quite some time ago in a land rover mag where they tried to make a 50mpg defender, I think they got pretty close, by pulling the roof off, front window off, doors off (replaced with cardboard) , seats out and I think they wrapped the vehicle with a clear packing film to smooth out the surfaces.

Yes I remember that, it was a 90. I could strip it to the bone yes, but as someone said elsewhere, its a work truck? if it ceases to be of use as a work truck because of your mods (or deletions) then you may as well get something else.

[western]

Ah thanks for that. so at 55mph I'm turning about 2350rpm without o/d

and presumably 1950 rpm at 55mph with o/d

so one last part of the conundrum, what would the rpm be at 60mph with the disco box. Anybody?

Also can you tell what speed you engage o/d in top , I mean what speed would you drop out of it?

Also do you find it gives better mpg with o/d, or more relaxed cruising, or both? Oooo this is getting good!

I usually engage my OD when in 5th at around 55 to 65 depending on the road, if it's got s slight incline, I normally leave OD out until I'm near or on the top of the climb.

most dual carraigeway & motorway driving is done with OD engaged, but depending on how good the traffic is flowing, OD engaged is quieter than just 5th gear without OD.

[Eightpot]

I'm not totally convinced the weight makes all that much difference - it seems right that it should, but maybe the torque characteristics of the diesels mean it doesn't.

I've been monitoring my fuel useage for a couple of years now in my Rangie ambulance (with 2.8 Isuzu turbo diesel) - while we were in Africa I was getting a steady average over a tankful of 29mpg when doing distance driving on fast dirt roads, and the all up weight was usually sitting between 2.6- 2.8 tonnes.

It's all stripped out now and weighing around 2.1 tonnes, and if I sit on the motorway at 65 in overdrive, I get around 32mpg.

A lot of energy must be lost through the 4wd system and the weight of all the propshafts, diffs, gears and big heavy wheels the engine has to turn all the time. And then we get excited about fitting a Kenlow fan to save energy

[zoltan]

The weight issue is most relevant when you come up to a hill and you have to turn some of your precious kinetic energy into potential energy. Irrespective of what powers your beast you have to add energy into the system or lose speed

[Daan]

Weight matters on acceleration, but once you are going it doesn't matter much. So the more stop start you do, the more it matters. The comment on lost energy in all the gearboxs is also important. Hence my suggestion of freewheel hubs and a 2wd conversion. Also, adding an overdrive is effectifely adding another gearbox, which isn't great from the drag point of view. Also, it is a shame that an LT77 has direct drive in fourth, it would be preferable to have direct drive in fifth from a consumption point of view.

Daan

[TheRecklessEngineer]

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

Ah yes, that sounds better. I'm a bit fuzzy on how economy varies with rpm - the diesels in my day job are fixed rpm.

[simonr]

Ah yes, that sounds better. I'm a bit fuzzy on how economy varies with rpm - the diesels in my day job are fixed rpm.

The higher the rpm, the worse the economy. They will have picked an rpm and designed the engine such that at the normal working load, it is running at somewhere around 80% of the peak torque that it can deliver at that rpm - so 80% throttle. At a guess!

Si

[Yostumpy]

The higher the rpm, the worse the economy. They will have picked an rpm and designed the engine such that at the normal working load, it is running at somewhere around 80% of the peak torque that it can deliver at that rpm - so 80% throttle. At a guess!

Si

So then, the 1.41 t/box is perfectly suited to the 300tdi, in its original design perameter, the fact that people now like to travel around faster in their landies than they did 15 / 20 years ago, AND the useage of the trucks themselves has changed, means that they are now undergeared for their usage, unless of course one uses one's landy as nature intended. Imagine if in '94 LR brought out a 110 capable of a sustained 90mph with a 6 speed box!!!! Thats L reg IIRC, what cars were about then.... If you think back that far, all cars were much slower altogether. We seem to have gone way OT but its an interesting thread none the less.

[vulcan bomber]

So then, the 1.41 t/box is perfectly suited to the 300tdi, in its original design perameter, the fact that people now like to travel around faster in their landies than they did 15 / 20 years ago, AND the useage of the trucks themselves has changed, means that they are now undergeared for their usage, unless of course one uses one's landy as nature intended. Imagine if in '94 LR brought out a 110 capable of a sustained 90mph with a 6 speed box!!!! Thats L reg IIRC, what cars were about then.... If you think back that far, all cars were much slower altogether. We seem to have gone way OT but its an interesting thread none the less.

I personally think the 1.4 box is fine for every use, my 200 tdi is standard other than i've been at the pump with hand tools, with a 1.4 box it will pull all the way to the pumps govenor, on a 1.2 box i found it would always slow down in 5th unless you were going down hill, there for i didnt see i as an improvement. I did 290 miles last weekend at a happy 65mph, just a tad noisey

[cackshifter]

Going back a way, Cummins tuned their 14 litre motors for economy by upping boost and limiting revs (2100 down to 1900 or therabouts), and getting the same power at lower speeds, and therefore quite a torque boost . There were a few other things - like a smaller oil pump and lower oil pressure to reduce parasitic losses, but that was the gist, and this had to be combined with raised gearing to match. There was quite a fuel saving, around 10% I think, they were attemping to match the Gardners which were also very economical, again only revving to 1850rpm. However I think you might need more gears in a defender - but you might get the same effect with a 1.2 transfer box, and keeping the revs down.

[Yostumpy]

I believe what is needed here is a gear that is between the 1.4 and the 1.2, say 1.3, that ashcroft could make, that would indeed be the best of both worlds, and it could be a retro fit cog, as they do with the 1.2. Now that would be good.

[FridgeFreezer]

Custom ratio LT230? Not as easy as you might hope - http://forums.lr4x4.com/index.php?showtopic=72643

[muddy]

Why not do some maths for final drive ratios for 1.4 and 1.2 boxs crossed with various tryre sizes (235/70, 245/75, 235/85, 255/85 etc etc)

Sure you can find a happy medium somewhere.

Will.

[Daan]

1.2 will be perfect for your requirements.

Daan

[rusty_wingnut]

I find to make a 1.2 work in a standard 300tdi you need to rework the intake pipework, removing that poxy plastic restrictor!

[Yostumpy]

I looked for ages to try and find a set of 255/85, as I believe they are the optimum size gearing wise, look right etc but to no avail. I didn't need /want MT's so at's would be ok, like the cooper st, but too much wonga for me. I run Avon Rangemasters 7.50's, not everyone's (aynyone's?) cup of tea, but they do me, last well, and I pick them up as new / little used spares, for not much, (last pair brand new £100 pair). If I go down the 255 route, I'llneed 5, then keep an eye out for more for the store cpd. This is the reason i originally fitted 1 ton rims.

Rusty, does removing the elbow restrictor (you mean the bit just inside the wing) make that much difference. Got a decent photo of how you overcome this heinous obstruction. Surely tho' this is nothing compared to being squeezed thro the air filter.

[rusty_wingnut]

Having just completed a jaunt to Liege and back this weekend with my free-er intake and a 1.2 transfer, I dare say the cruising speeds aren't much different to a 1.4. I find I can reach 72mph at what feels like a decent throttle margain but give me an incline and it's down to 65mph. Around town 1st was a little tough when loaded on some of the hillier starts.

I got 280miles from a full tank in the 90.

I can only summise that trying to push the brick shape of a Defender through wind at anything over 65mph is going to hurt the economy. I wonder if the Ibex has less frontal area and a better windscreen rake angle?

[Daan]

Having just completed a jaunt to Liege and back this weekend with my free-er intake and a 1.2 transfer, I dare say the cruising speeds aren't much different to a 1.4. I find I can reach 72mph at what feels like a decent throttle margain but give me an incline and it's down to 65mph. Around town 1st was a little tough when loaded on some of the hillier starts.

I got 280miles from a full tank in the 90.

I can only summise that trying to push the brick shape of a Defender through wind at anything over 65mph is going to hurt the economy. I wonder if the Ibex has less frontal area and a better windscreen rake angle?

No on both counts, but it is heavyer. What is your mod on the intake?

Daan

[FridgeFreezer]

So you're running fatter rims with distinctly non-eco tyres, that's not going to help!

Pulling a set of road tyres off a scrap Disco or RR for a few quid and running them as your road-wheels will save a load, and if they're smaller in size then they may help the gearing as well as lowering the car.

I would look at calculating the power required to push the defender through the air at various speeds, I'll bet the curve rockets up as you get near 70mph, you may find dropping back a bit would save a load.