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Old 02-27-2012, 03:24 PM   #11 (permalink)
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wallace - '98 landrover 300tdi defender 110 hard top
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thanks for the graph, can't pretend to understand it tho', what are the small numbers on the graph ie 197 & 210. the left side is that turbo pressure? ie at full chat it uses 197 thinggies, and at .5 bar it uses 230 of them all at about 1500-1800 rpm? also what are the dotted orange lines, pleaese explain to an idiot

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Old 03-01-2012, 08:51 AM   #12 (permalink)
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Well, BMEP, the vertical axis basically corresponds to torque, and the numbers are how much fuel is needed to produce a certain amount of physical work. (Lower is better)

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Old 03-01-2012, 03:32 PM   #13 (permalink)
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Originally Posted by yostumpy View Post
thanks for the graph, can't pretend to understand it tho', what are the small numbers on the graph ie 197 & 210. the left side is that turbo pressure? ie at full chat it uses 197 thinggies, and at .5 bar it uses 230 of them all at about 1500-1800 rpm? also what are the dotted orange lines, pleaese explain to an idiot
Hi yostumpy,
To expand on what jakobnev said. I've annotated the graph.

This isn't your engine, obviously, but your Rover's graph might look about the same.
The orange arcs are approximately constant power curves. The top curve is about 30 kW.
The left scale - bmep, stands for brake mean effective pressure - is the pressure in the cylinder pushing on the piston that can be used to move the car. 1 Bar is 100 kPa.
The little numbers are the efficiency given in grams of Diesel fuel per kW hr. Lower numbers = less fuel is better. The curvy lines that go through the numbers are the points with that efficiency.

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Last edited by mort; 03-01-2012 at 04:53 PM..
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Old 03-01-2012, 05:45 PM   #14 (permalink)
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Ok, thanks Mort. So , to recap, the 'correct' way to accelerate a turbo deisel, is the total opposite to that of a petrol engine with a vacuum gauge fitted. ie, short hard burst up to 1800rpm, as opposed to gentle , low vacuum throttle opening. I've been trying it for a couple of days now , but it does feel totally 'against the grain' to 'mash the peddle'. still been doing a fair bit of coasting, but the permanant 4x4 system on the land rover, takes a lot out energy out of the free ride. Getting a more used to it tho' and i'm using the kill switch I fitted at the weekend, a lights junctions etc..
As an aside, note to mods from a newby, as deisel and petrol are so very different, how about a seperate section as a 'one stop shop' for the dino boys,as some of the methods cant apply to deisels. You see i'm having difficulty in understanding exactly how a turbo deisel works. I've searched the forum and gone back 5 pages already. I keep thinking that when I plant my foot hard on the peddle,i'm pumping in loads of extra fuel thats going to flood the engine, but i begining to realise thats not true. i've always been quite easy on the peddle. If my mpg plummets this time, then its wrong for my truck, and I'll return to my old way. if its the same, I'll still return to the old way as I feel I'm being easier on my truck. if you know what I mean.
Cant wait for my first fill up, hope i'm not in 'negative equity'
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Old 03-01-2012, 06:24 PM   #15 (permalink)
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have been told by truck drivers that the proper way to drive a TD is to be light on the fuel feed. he was adamant about not calling it as throttle seeing as it was not a throttle.

of course this was for driving large semi trucks where power to weight ratios are rather horrible. he said that flooring it meant using lots more fuel for barely measurable increases in acceleration rates. perhaps with a smaller vehicle the gain in acceleration is worth the increase in fuel feed rate.

btw, i was under the impression that modern FI gassers did better with a heavy foot and short shifting. the reason being that fuel/air ratios remain constant even under heavy throttle.
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Old 03-02-2012, 08:49 AM   #16 (permalink)
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I accelerate my 3300-kg, 5.9L turbodiesel truck quite easily. Shift at 1,500-rpm or a touch lower (peak torque at 1,400-rpm, IIRC). Even with a trailer weighing somewhat more I don't find that harder acceleration is beneficial. On big trucks (lorrys) we don't ever give it more throttle than necessary to get to the next gear. "Rhythm" is what matters. Consistency. On those 10 thru 18 speed transmissions one would look up and learn (then practice) progressive shifting. Think of it as learning to waltz.

As a general rule-of-thumb, the highest gear at the lowest rpm is the best choice. So long as the truck does not "lug" one has made the best choice (especially on grades: don't downshift too soon).

So, "it" isn't about the throttle, but about the transmission gear. The single importance of the throttle is that it moves me between gears. And the gear choice is everything. I barely "use" the throttle, IOW.

The truck really needs nothing from you but strict attention to the road to determine shift points. The truck is "better" than you in the matter of greatest mpg is another way of viewing this. We work for the truck rather than the other way round. You might consider adding an Exhaust Gas Temperature gauge, and a Manifold Pressure gauge to be able to better listen to what you're being told. Low numbers of 600-F and 6-psi are good numbers for FE on my truck, for example.

Also, I'd analyze the times/distances your truck spends at highway speeds. While aerodynamic concerns are valid at lower speeds, the loss of utility may yet be present and cancel removal of the roof rack . . after all, a truck not used as a truck might be better replaced with another vehicle. To this end I recommend being able to calculate average kmh at the end of a tank-full (and on a calendar basis).

You might also contact the editor of CommercialMotor.com - Big Lorry Blog and ask if he knows of a link or a source to your stated interest. He's a very wide range of readers and contacts across the Commonwealth.

Now, I can't say comparing my truck to your has great equivalence, but if it is of help, then:

* With six forward speeds, and First being extra-low (a granny gear) I use it almost exclusively to get the truck in motion and am out of it almost instantly (unless crossing a roadway, etc). Getting all the mass in motion is my thinking (debate-able, according to other owners), but I prefer to set up that rhythm mentioned above. After all, the engine rise between gears is only a few hundred rpm.

* As Overdrive is the top gear -- and with the short axle gears of this truck -- most cruising in town is in Fourth or in Direct. As the goal of shifting is to arrive in the chosen "top" gear quickly, the "place" to shift (that point ahead on the roadway) must be amenable to such. Loss of momentum hurts, IOW. The weight of the vehicle, the mass, favor an even slower acceleration if a blind spot is ahead, traffic slowing, a turn is coming up, etc.

* Planning the trip I am making is beneficial. Delivery services here in the States use routing software to eliminate turns across traffic and to travel as many miles as possible at a steady speed. So a few miles out-of-route on longer trips is beneficial to this, and even in travel around town is an extra half-mile a good thing if it avoids several full stops or traffic lights. (I may think I "know" the best route, but have been proven wrong by consulting this form of GPS aid prior to travel).

* Most of all, note military or other convoys that are heavily loaded. They take no account of other traffic as their weight and gearing preclude the rapid acceleration to which we civilians are accustomed. A steady pace that emphasizes longest life (drivetrain ease) is therefore beneficial. Etc.

I see that my fuel consumption is about an average 10.6L/100-km. Look forward to what yours can do and how you've improved it in percentage terms.


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Old 03-02-2012, 11:14 AM   #17 (permalink)
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I feel it's a mistake to focus on acceleration techniques when getting in to eco-driving/hypermiling. Why? Because it's an "it depends" scenario. Saying high load acceleration is always best is wrong. "It depends", for example, on what happens immediately after the high load acceleration.

If you have to brake for any reason following high-load accel, you've thrown more fuel away than someone who does light load accel and avoids having to brake.

Keeping cruising speed down, using the highest gear you can without lugging, and minimizing use of the brakes (or engine braking) will yield much more.
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Old 03-02-2012, 12:45 PM   #18 (permalink)
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Lots of conflicting advice from you guys.I guess i'm trying to run before i can walk. 'Mashing the peddle' does feel wrong, and i only do it when I can see its of benifit, ie opening road. I know that ' jakobnev' must use this method, but i'll think i'll just go easy, with lots of coasting and kill switches, and go from there. (tank to tank) After all, Rome wasn't burnt in a day.
'Slowmover' thanks for a compehensive reply.
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Old 03-07-2012, 11:04 AM   #19 (permalink)
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I tend to get on up to speed when it looks like I get to stay there. If it is questionable, then I go all "light foot" on it. The 6 banger makes so much torque in the 1200~1500 RPM range, I feel it does pay off to get it over with.

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Old 03-09-2012, 07:57 AM   #20 (permalink)
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To mash or not to mash?

First off, I think you'll have difficulty measuring the effects of your driving until you can get real-time mpg feedback. I tried all sorts on my last car which didn't have any instrumentation - current car has a mpg readout as standard and there's really no substitute for it.

I don't have a land rover- but I can offer what I've found out on my 1.4 TDI vw engine. And that is a light touch on the accelerator, drive as slowly as you dare and keep to a constant speed. It can help to let the car slow going uphill, then take advantage of gravity going down the other side. I keep revs 1500-2000rpm.

I've tried the pulse and glide and it did not help on a TDI! It also happens to be impractical IMO here in the UK. Traffic is too dense and most other drivers expect you to go as fast as possible. Don't know where they get their cheap fuel

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