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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old November 8th, 2011, 09:26   #1
Vekke
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Default Hypermiling videos to better fuel consumption

Here you can find few videos how you should drive your TDI if you want to maximize its fuel economy:

Cold start techniques:
http://www.youtube.com/watch?v=bz2cBBD5TCU
City driving:
http://www.youtube.com/watch?v=THkVciVpmxs
Highway hypermiling uphills
http://www.youtube.com/watch?v=f7LZIyu9EN8
Highway hypermiling downhills
http://www.youtube.com/watch?v=Ke2ATgnuFWg

General rules:
- accelerate fast with full throttle to posted speed limit
- Keep revs between 1800-3000 +-200 rpms depending on the motor and gearing.
- glide in neutral as much as possible (at least all downhills)
- dont use the brake pedal so lots of anticipating
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Last edited by Vekke; July 12th, 2013 at 04:40. Reason: Corrected links so they should work again.
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Old November 8th, 2011, 21:04   #2
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Cool thanks for your efforts.
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Old November 9th, 2011, 16:42   #3
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Nice videos. Good work on the fuel saving front line, as always.
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Old November 9th, 2011, 19:28   #4
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Quote:
Originally Posted by Vekke View Post
General rules:
- accelerate fast with full throttle to posted speed limit

Really???
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Old November 10th, 2011, 00:03   #5
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Yes. That comes the fact that turbo diesel works at best efficiency in the bsfc map with full throttle. Lower the figure in the map, lower the fuel consumtion.
http://www.google.com/imgres?q=bsfc+map&um=1&hl=en&client=firefox-a&sa=N&rls=org.mozilla:fifficial&biw=1280&bih=77 0&tbm=isch&tbnid=2jvTkVVwwgqf0M:&imgrefurl=http://www.dodgetrucks.org/gallery/showphoto.php%3Fphoto%3D10192&docid=fy-cGu4xMog-jM&imgurl=http://www.dodgetrucks.org/gallery/data/500/TDIdiesel1_9L_ALH_BSFC_map_with_power_hyperbolae.p ng&w=403&h=450&ei=ynO7TtSfKonRhAf62dCoBw&zoom=1&ia ct=hc&vpx=1027&vpy=126&dur=3346&hovh=237&hovw=212& tx=138&ty=110&sig=115318704233533286321&page=1&tbn h=131&tbnw=117&start=0&ndsp=24&ved=1t:429,r:5,s:0

That map is for ALH engine, but never pump duse TDI maps are similar. The sweet spot is usually little bit lower throttle position but still I would recommend on acccelerations to use full throttle, because the difference between sweet spot figure and flat out is smaller than the difference in torgue. More torque means faster acceleration.

Also when you tune your engine to more HP the engine will work more fuel efficient and lower the fuel consumtion. All the time when you make more torgue the fuel map figures get smaller... That is the case if dont make more horsepower with black smoke (extra diesel). So the air to fuel ratio still needs to be correct.

With that engine map I would try to accererate from 1700 to 2300 (that is the same curve than in my old seat) If you go lower the engine will drop from boost curve too much and it will take more time to get the boost up. Of course the points always depend on the gear ratios. On my lupo nothing happens under 2000 rpm and gear ratios are so tall that I have to rev it to 3000 rpm or I would drop under 2000 rpm with next gear.

And for example if you do push and glide from 45 mph to 55 you should use 4th gear instead of fifth. Both sit inside the torgue curve but 4th is shorter so car will accelerate faster to that posted speed limit.

The lower fuel consumtion with lower engine speeds is related to engine RPM`S. Here is a efficiency map of one engine.
http://www.dodgetrucks.org/gallery/s...=10171&cat=500
So if you can tune your engine to make more torgue at lower rpm`s its bsfc map will get better. Usually there will come problems with first clutch. When you install better cluctch with transmission gears. So the pressures to engine components are much greater with low rpms than they are at the high rpm section. 1.9 TDI can easily handle 250 Nm and at stock clutch will brake at about 300 Nm. If you make it to produce 400 Nm you have to install stiffening plates to engine and stronger clutch. Now the weakest point is the gearbox witch will brake frequently with that kind of power and torgue. So you need to install stronger gearbox also from some high power engine. If you have more cylinders like truck engines they can make the torgue lower rpms because the engine pulses are smoother even though they are high. That map at doge truck is propably from big dodge truck so its not a tdi but same priciples apply .
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Last edited by Vekke; November 10th, 2011 at 00:23.
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Old November 10th, 2011, 22:04   #6
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so what i'm being told is that it is more efficient to push the accelerator to the floor and rev the engine up? i was always told that gradual accelerations, shifting at 1800-2100 will yield the best MPG's. I feel that in testing, if i drive more conservatively, i get better mileage. should i raise my IQ to reduce smoke under heavy acceleration? i just can't believe that faster acceleration and higher RPM's will not hurt fuel economy.
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Old November 11th, 2011, 00:44   #7
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Yes if you have fingered the IQ set the value so that car dont smoke so much under full load. After that test one tank and see the results. With revving up you should not definetely pass the 3000 rpm mark. In many TDI the thumb rule last change point is already at 2500 rpm.

You should be able to see clear difference if you accelerate modesty at the moment. Also its more fun to accelerate fast . Note that your fuel consumtion only gets better is you make the accelerations to that posted speed limit so that you dont have to press brakes after you have reached the speed limit. So obrserve the other drivers is the key to be able to accelerate fast and save fuel while doing that.

With flat out your fuel consumtion is very high, but the time is much shorter than slow acceleration. ALso the engine get more power from the fuel at full load so that helps also. If you measure the difference in for example 1 mile level stretch with your old and new technique difference should be visible.

This is also one of the reasons why hypermiling is faster way to move in city driving. You accelerate fast from driving lights so you have better changes to make through the next ones (of course this depends on the situation you dont want to accelerate fast towards. red lights or ones which you can predict that they will turn red when you rech that point.
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Old November 11th, 2011, 05:10   #8
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On the highway, I was under the impression that coasting in gear was more fuel efficient that coasting in neutral

But good videos nonetheless. Thanks for taking the time to film and upload these. I try to drive like that in town.

The end of this video had me laughing: http://www.youtube.com/user/TunekoLtd#p/u/3/f7LZIyu9EN8

"Now I have lost my truck and will have to find a new one". Sounds really funny if the context is not known

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Old November 11th, 2011, 07:02   #9
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Its always more fuel efficient to coast in neutral. However if you driving speeds that are well over 65 MPH its more fuel efficient to stay in gear and feather the trottle (not in engine brake mode), if you have a certain avg speed you want to maintain. So when putting the car to neutral you start to loose speed very fast it is more wise to stay in gear. When doing P&G if your glides start to be same time as your pushes its more wise to drive steady throttle. So wind resistance is already so high that it stresses the engine more than the gain will be with P&G. With stock TDI the limit is about that 60-65 MPH. IF you start driving behind a bus that speed is raised to about 7 MPH. So you can drive about 7 mph faster with same fuel consumtion.

Remember basic rule is that it is more fuel efficient to drive the whole trip with same speed for example at 70 MPH rather than half at 60 MPH and other half 80 MPH. Steady speed is more fuel efficient and the avg speed is the same .

To get most of gain from P&G takes practice and time.

More similar videos will follow.
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Old November 11th, 2011, 07:46   #10
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Quote:
Originally Posted by K.I.T.T. View Post
On the highway, I was under the impression that coasting in gear was more fuel efficient that coasting in neutral
Coasting in gear is infinitely fuel efficient above ~1200 rpms. The injectors won't fire and no fuel will be used. This is best used when you know you will have to stop soon, so you coast in gear in order to use no fuel, and slow your car down.

However on the highway, you will lose a lot of precious speed coasting in gear, and neutral will be more efficient.

I think of coasting in gear as an efficient brake pedal.
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Old November 11th, 2011, 12:41   #11
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Its not coasting in gear if you release the gas pedal. Its called engine braking. If you want to move forward and save fuel it is not wise to brake in any way. Driving in neutral also brakes with drag and rolling resistance but those are valid all the time.

Only time engine braking is more fuel efficient is when the cars speed is slow like 20 MPH and you know you have to stop. Of course there are situations where its more wise to engine brake than coast in neutral but if run into that kind of situation you havent been successful in traffic anticipation.
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Old November 11th, 2011, 13:12   #12
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Thanks for the videos.

A rule of thumb I use is if you are able to maintain your desired speed while coasting in gear( engine breaking) it's more fuel efficient because it keeps the motor spinning without fuel. Going down a steep hill for example Or if you are wanting to slow or know you will have to stop ahead.

Otherwise you are better of truly coasting in neutral.
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Old November 11th, 2011, 13:42   #13
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No you will just have to start slowing down with neutral coasting much before. Or if you encounter so steep downhill that you have to start enginebraking you have come too fast to that hills highest point.

Slowing down to 30 MPH from 62 MPH
With engine braking you can start that engine braking about 600 yards before the 30 mph speed limit
When coasting in neutral that same distance is over 1000 yards, depending on your aero, windspeed and its direction, cars weight, uphill or dowhill, rolling resistance etc

These are the rules that give you the best fuelmileage. Not necessarily you fastest to places but more fuel efficient. This is last post I try to clear this neutral coasting in this thread. I will make a video to prove it if its so hard to believe it.

In USA you have those long and deep downhills where you have to slow down so then the engine braking is the best way to do it if you dont want to get speeding tickets. But you can also try to come slower to that hills highest point so you wont have to overspeed so much in the downhill. There are few that kind of hills in finland also and speeds can go from 62 MPH to 90 MPH and the limit might be that 62MPH. If you come to hills highest point driving 42 MPH your speed will then be 70 and in finland they dont give ticket in that small speedings.

If hills are longer then you just have to put the engine brake on but those situations are minimal at least in finland. You cannot write or tell a driving rule that fits all situations that is just impossible.

What I call a general rule what tells do you know how to drive fuel efficient is that you should be able to have same fuel consumtion average that you had before you go over a "medium" hill and return to same height over sealevel. That is just a basic physic law also. If done correct it can be even better at the other side due to BSFC map correct usage (ifyou normally drive with steady throttle/cruise control).
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Old November 11th, 2011, 14:09   #14
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Thanks
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Old November 13th, 2011, 15:38   #15
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Here is the gliding in gear VS gliding in neutral video:

http://www.youtube.com/watch?v=CPvv08oFKKY

I will check the gliding in neutral result with correct start point next time I drive pass that same place on next week.
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