Getting Max Fuel Mileage

[VWRacer]

My brother is thinking about buying a diesel VW, but is interested in max fuel economy rather than power, as he is on a very limited budget. Assuming he can't find an EcoDiesel, what is the best combo? I'm thinking a TD with...

5-sp manual trans (Duh!)
Increased boost and disabled enrichment circuit
Lower fueling via the max fueling adjuster
Disable (open) the boost limit switch
Advance timing
Lower idle speed
Switch to slightly taller tires

What do you guys think?

[QuickTD]

Increased boost and disabled enrichment circuit

High boost is counterproductive when you are shooting for economy. You only want to run as much boost as is necessary to burn the amount of fuel injected, any more just increases pumping loss and will hurt fuel economy. The ideal setup would be a naturally aspirated engine with the fueling turned down to about the 35hp level. No sense in using a turbo and then crippling it by turning the fuel down to NA specs...

[RAMMSTEIN]

Yeah, except "retard timing"

The early .85mm setting was considered 'economy', while 1mm was for 'performance'.

Advanced timing on TDI yields higher fuel economy.

How is it the opposite on IDI's?

[VWRacer]

Interesting conversation!

I recall the mileage boost with Callaway's kit in the early 80's. I wanted to buy one back then, but couldn't afford it in those days. In any case, I would be interested to read any articles that address the question of timing and boost as regards fuel economy.

Also, Rammstein is right about advanced timing improving fuel economy in TDIs. Another mileage improver is bigger injectors (the apparent benefit coming from dumping their fuel load in a shorter amount of time). I suspect that Giles' technique of shaving the back sides of the pintels would have the same effect.

Also, IIRC the EcoDiesel uses a smaller-than-TD turbo for continuous boost, but uses the NA fuel pump to get about 6 more HP and better fuel economy than the NA cars. This lends further credence to the notion that added boost alone can improve fuel economy slightly, in spite of its pumping penalty.

Experimentation is the mother of conversation, though, and this sounds like an ideal recipe for back to back testing! :lol:

[ricosuave]

dont forget to max out your tire pressure as well!

[VWRacer]

Yep...absolutely, Rico!

[AntonUK]

Suppose that extra boost will just raise intake temp and make negative effects unless your going intercooled..

[SMOKEYDUB]

You can also screw around with the lda and making it travel further when not creating boost as in creating more spring pressure so it staysup longer.

my 2 cents

Jeff

[QuickTD]

I would agree with the turbo = better economy to a point. A naturally aspirated engine that was already smoking, even slightly, before adding the turbo kit would very likely realize a gain in both fuel economy and power. What I'm suggesting is detuning a NA engine so that it cannot be made to smoke, even under full power. Sad as it may perform I'm thinking it would deliver the best economy.

[DieselsRcool]

I have noticed an increase in mpg with changing from the 130bar injectors to 155bar. My guess it's due to the higher spraying pressure and better atomization. I also notice better power just off idle. This could be due to retarded timing caused but delayed pop.

[web]

Loosely related... what's the BSFC of our engines roughly, or comparable small automotive diesels?

[fspGTD]

Loosely related... what's the BSFC of our engines roughly, or comparable small automotive diesels?

Now that's the right question to ask... minimize BSFC (brake-specific fuel consumption) and you will see mileage being maximized.

I wouldn't be quick to accept the notion that the most efficient engine would no naturally aspirated.  I feel in my gut that the turbo would be more efficient.  You see when looking at the BSFC maps of the naturally aspirated diesel and 1.6lTD, that although they both have a similar minimum BSFC, the 1.6lTD has a broader "plateau" of minimum BSFC.  So what I think is, when you're actually driving it (the TD) you will see better real-world mileage.  From a thermodynamics standpoint it makes sense that the turbo could add efficiency, because it can make more torque (IE: smoke-free) so can be run at lower RPMs thereby reducing engine RPM-related friction (IE: bearing drag, etc).  The only cost is a little extra backpressure, but I think that's more than made up for by the engine thinking it's bigger as a result of the boost pressure.  The turbo recovers some portion of energy that would normally be lost as heat out the exhaust.  Granted, the turbo is not perfectly efficient itself, but I think it's true that a turbocharged engine is more efficient than a naturally aspirated engine with enlarged displacement (so the two engine being compared develop same amount of power or torque output.)  This is particularly true with a turbo-diesel, as CR doesn't need to be reduced.

There are BSFC plots (of RPM vs load) in some of the SAE papers...  off-hand I only know that the TDI engine broke below the 200 g/kWh level.

Edit: I looked up the BSFC maps - The 1.6l diesels are around 260 g/kWh.

For 5-cyl IDI TD motor, see figure 54: (note:bsfc contours are hard to read, but range from 261 to 562)


For 4-cyl 1.6lTD motor, see figure 36: (note:bsfc contours range from 264 to 977)


And those of you with the 1.5lD SAE paper, can see a BSFC plot for this motor on page 111 (figure 55.)  The minimum contour is 250 g/kWh, at about 80% throttle, between 2250-2500RPM.

[farkman]

One of the easiest changes to make would be replacing fluids with synthetics. I don't know what kind of temps your brother will be driving in but I would start with an oil in the thin 40 weight range. There aren't many thin 40 weights which are diesel and VW 505.00 rated, so I would do a 50/50 mix of Amsoil Series 3000 5W-30 and their European Car 5W-40. I will be using this mix when I change my oil tomorrow. It will be costly, about $35-40 US, but it only needs to be changed every 10,000-14,000 miles, with a oil filter change half way. For gear lubes I would suggest Redline MTL since it's the thinnest gear lube you can easily get (70W-80). However, if the car's going to be used in a warm climate mix in some Redline MT-90 (75W-90) to give better wear protection from the increased viscosity. I would have suggested Amsoil S2000 gear oil but they discontinued that a month or two ago. But if you can get it I would recommend it. I have that in my car now and is real good, I gained a good 3 mpg with it.  Finally regrease the rear wheel bearings with some real good grease like Amsoil Series 2000 racing grease. My apologies if I sound like someone who works for Amsoil, I don't, I just really like their products and it's about the only quality lubricant I can get easily where I live for a decent price. Oh, and a 2.5" exhaust system would really help too   .

[vwmike]

I wouldn't be so quick to switch to synthetics. Synthetic oils carry a detergent factor to them that tends to clean out all the "crud" around seals which will cause them to leak. So, if you want to run synthetic be prepared to change all the associated seals (engine or trans).

[VWRacer]

Very interesting discussion, guys. Whether the ultimate fuel mizer engine is NA or turbocharged is not really the issue. My brother's needs are more 'real world'. He lives in the NW and is looking to get better fuel mileage than his gasser 4wd Ford pickup gives him (~12 mpg around town, maybe 15 on the highway). He told me he could make more trips to visit family outside the area if he could get 2 or 3 times better fuel mileage, so is looking at a VW diesel. The basics of what to do to get the best mileage are well covered here, and will hold him in good stead should he end up buying a car or caddy.

BTW, I snagged this fuel chart off the TDI forum a couple of years ago and thought you might like to have a look at it.



The solid black curved lines are grams per kilowatt-hour, starting from 200 at upper left and going up to 500 at lower right. From the right edge, you can see the hp curves from 10 to 90. By following the hp lines to the desired RPM one can see the fuel required at that hp. For instance, follow the 50 hp line to the upper left and you'll see that the most efficient a TDI engine can get is about 197 gm/kwh at ~1750 RPM. Kind'a cool, eh?  :wink: