modifying the diesel for more economy

[theunchosen]

The only issue I could forsee there would be the drive train would probably not much care for that. It would have to run a compression without having an expansion cycle to power it. You would also have to pump air through the other two cylinders even if they stopped injecting. IF you disconnected them from the crank thats different but way more complicated.

[Ernie Rogers]

I worked with Kerma last summer to attempt to improve the fuel economy of my Beetle TDI, by "chipping." We did not find a change that improved mileage. Injector nozzles were changed also and that gave no noticeable improvement.

Ernie Rogers

Originally Posted by Southcross

heated fuel yes...

I suspect though, if you tried to lean out your injector pump your EGTs would go through the roof and cook your turbo. I'm gonna say no, unless you wanted to invest in watermethanol injection/etc to bring them back down.

What kind of vehicle? On the VW TDI engines, you can chip them... while it gives the engine more power/performance, if you keep your foot off it (drive it normal, hypermile would probably make a huge difference), its been reported to increase efficency by 5-10% (hypermiling would likely do even more) due to better timing and mixture.

If I had to guess, without knowing your engine/enginemanagement... timing, timing will have the greatest single effect you can do without external modifications (chip, water-meth, etc)

[Big Dave]

The commercially available diesel engines are pretty well sorted out from an economy standpoint. I, too have tried and gotten only trivial improvements.

Diesel vehicles can get better MPG with gearing changes. Diesel vehicle have to use the same gearing used for gas engines because of economics of scale.

Erni'e TDI Beetle uses a 3.89:1 ratio, but the TDI is very torquey and could easily push something in the range of 2.93 or 3.08 and such ratios will greatly improve MPG, particularly in conjunction with aerodynamic improvements.

If you think you can improve MPG with engine mods, you are kidding yourself.

[caissiel]

I had a 98 GM 6.5L Diesel for 9 years, I was getting 16 MPimpG with this truck and went to the dealer on warranty and no results. When the engine Warranty was over I did the open 3" pipe exhaust, and made and installed a Mechanical Turbo Waste Gate Control. I kept the Boost at 8PSI Max. Well later I made a turbo electronic fooler and set it at Max 6 PSI, while the Mechanical controlled it at 8 PSI. The fuel Milage improved from 16 to 23 and the truck was like a completely different truck. I could beat a GM 350 1/2ton that weight 2000 LBS less on the line and could haul my trailer with a 2 MPG advantage. When I accelerated I just did not floor it because I knew the heat was building fast as the left manifold hi temp warning held me back. Not worst then when it was stock though. These trucks were afull for heat with no Intercooler.

[roflwaffle]

Originally Posted by diesel_john

I'd like to just take out two pistons once i get up to cruising speed, but i haven't figured out how to do that yet.

Unless you have a significant downhill/low load drive, or have basjoosed your VW, taking out two pistons won't do much. Even then, the stock tires are so small that increasing wheel/tire diameter can cut engine speed a good ~30%, even if you have a trans that already has the engine turning at ~2100rpm at 55mph.

In terms of FE word is that the biggest pump side gains come from fiddling with the dynamic timing advance, since the static timing range isn't wide enough to help much. Before doing this you also need to check internal pump pressure since a drop will retard the dynamic timing mechanism, which means worse mileage. In fact, since the diesel today has much lower viscosity than the diesel of the 1980s, even if the pump was in tip top shape we would still need to at least reset the internal pump pressure. Anyway, fiddling w/ dyamic timing ]ain't too bad, just different springs/smaller shims.

You can also get a turbo pump/turbo, and use something to cut off the boost pressure connected to the LDA on the turbo pump to get super lean or stock fueling on demand from in the cab. Supposedly a stock VNT turbo from a TDI offers a small efficiency/great power improvement with an IC and appropriate boost.

[theunchosen]

As Caissel noted and I forgot to mention, An intercooler and duping the ECU would be huge improvements. The intercooler would be important to slightly lower combustion event temps washing to the cylinders. It also would let you get more air into the cylinder for a tiny bit of extra pumping.

Power gains sound a little odd, but the mpg claims sounds about right since he was cutting 2 psi out of 22 he was running 10% leaner than a diesel does anyway.

[Deezler]

Originally Posted by Ernie Rogers

I worked with Kerma last summer to attempt to improve the fuel economy of my Beetle TDI, by "chipping." We did not find a change that improved mileage. Injector nozzles were changed also and that gave no noticeable improvement.

Ernie Rogers

Really? I have Kerma tuning also, and I would definitely agree that he is not the premier TDI engine tuner. I noticed a definite improvement in mileage from the bosio PP520 nozzles, but nothing concrete from the engine tuning. But I think it helped, especially in conjunction. There are logical reasons why altering the engine calibration can affect mpgs. Some of them are trade-offs for emissions though, which is kind of a selfish adjustment to make. On the other hand, trading total carbon emissions for a little NOx is worthwhile to some (depending on the magnitude!).

The nozzles provide better atomization of injected fuel and that should have a direct benefit on combustion.

If you drop the EGR rates way down, you get way more fresh air into the cylinder. Assuming you've started from a relatively high EGR %, this improves combustion efficiency. Also, if you have more fresh air coming in, you can reduce the amount of turbo boost required to get a certain combustion efficiency and thus engine power output. Less requested turbo boost means lower exhaust manifold pressure means less pumping losses, which should directly translate into better mileage.

Advancing the injection timing should also have a definite effect upon power production for the same amount of fuel injected. Trouble here is that most modern diesels come pretty well optimized already. If you inject too soon, you will not make more power.

Finally, pushing the engine to a higher overall power output can help you to accelerate through the higher BSFC portion of your engine map, and make it possible to run more extreme gear ratios and still be able to accelerate. Do this at your own risk however!

What no one seems to be saying yet in this thread is that you can't just lean out the air fuel mixture on a diesel and expect MPG benefit. Lean out the mixture and all you've done is REDUCE POWER! If you leaned out your entire engine operating map, to make your vehicle travel the same speed down the road you would just put the pedal down further and get back to the same amount of fuel to make enough power. This is why diesels don't have much room to improve (via tuning). In a diesel the amount of fuel injected is directly proportional tot eh amount of power made (assuming reasonable injection timing and air/fuel ratios).

[tasdrouille]

Ernie, when you say you worked with kerma to chip your TDI for fuel economy, how did you measured fuel economy when making changes to the ECU maps?

Using vag-com to log fuel consumption, my experience has been that advancing start of injection timing 3 degrees over stock (everything else remaining the same) led to more or less 5% increase in FE.

Tweaking the EGR for max recirculation also lead to an additional 3-5% in FE when combined to a 6 degrees timing advance over stock. When using vag-com or a scangauge to read fuel consumption, increasing EGR will look like fuel consumption went up, because the IQ value was offset upward when you change the EGR rate, which is deceptive, you need to look at tank-to-tank FE. Also, since increased EGR retards the start of combustion event, you need to advance the start of injection timing in order to preserve optimal FE.

[Ernie Rogers]

Tas,

I am amazed by the depth of your thinking. The textbooks say that EGR shortens ignition delay.

I haven't played with fuel economy since the experiments last summer. My normal procedure was to fill my tank to the neck at the Tooele truck stop area on I-80, west of Salt Lake City. I drive west to the Nevada line (Wendover) 100 miles, then turn around and drive back to the truck stop and refill. All on cruise except the start, stop, and turnaround. The highway is nearly flat and usually has very light traffic. I monitor my speed with a GPS, and use GPS for distance. I also drive fast for one hour before beginning the test. Results are fairly reproducible, about +/- 1 mpg (in 65).

My scan guage is running during the testing. Here is something to ponder. About 10 miles out of the truck stop, the highway pavement changes from smooth concrete to smooth asphalt. I see an abrupt drop in fuel economy on the ScanGuage when I transition from concrete to asphalt, maybe a few mpg.

On a trip near the bay area in California, I crossed a pavement change where I-580 connects to I-5. I-580 is smooth concrete and I-5 is rough asphalt. My ScanGuage reading dropped by about 10 mpg. Repeat: From about 75 mpg to about 65 mpg--about a 15% difference due to pavement change from smooth concrete to rough asphalt. This effect has been documented by others.

Ernie

Originally Posted by tasdrouille

Ernie, when you say you worked with kerma to chip your TDI for fuel economy, how did you measured fuel economy when making changes to the ECU maps?

Using vag-com to log fuel consumption, my experience has been that advancing start of injection timing 3 degrees over stock (everything else remaining the same) led to more or less 5% increase in FE.

Tweaking the EGR for max recirculation also lead to an additional 3-5% in FE when combined to a 6 degrees timing advance over stock. When using vag-com or a scangauge to read fuel consumption, increasing EGR will look like fuel consumption went up, because the IQ value was offset upward when you change the EGR rate, which is deceptive, you need to look at tank-to-tank FE. Also, since increased EGR retards the start of combustion event, you need to advance the start of injection timing in order to preserve optimal FE.

[diesel_john]

Ernie, Good to hear from you. Did you notice much difference in wheel slip going from concrete to asphalt? There is the ground effect. But maybe rolling resistance is the biggest. I noticed the roads that are very noisey to require more fuel. A rise in shock or tire temperature could indicate more fuel. Hot asphalt deflects more so your driving up hill both ways.

Do diesels run better on foggy days despite the heavier air?

I am getting that leaning out most diesels don't help much cause they are already leaned out. Am slowly advancing the static timing. I am assuming that advances the dynamic timing also on the mechanical rabbit. I suppose the head gasket will blow if I stretch the head bolts too much. Piston slap noise definitely is louder, so I am carrying more pressure over TDC. Guessing the max. VW spec. is close to the max. MPG.

roflwaffle, correct me if i'm wrong, you obviously know a lot more about pumps. how much timing advance is too much? when EGT's drop? On the mechanical system should i raise the internal bypass pressure?