VWDiesel.net The IDI, TDI, and mTDI source.
Engine Specific Info and Questions => IDI Engine => Topic started by: VWRacer on November 14, 2004, 09:57:00 pm
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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?
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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...
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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?
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Interesting conversation! :D
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:
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dont forget to max out your tire pressure as well!
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Yep...absolutely, Rico! :D
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Suppose that extra boost will just raise intake temp and make negative effects unless your going intercooled..
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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
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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.
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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.
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Loosely related... what's the BSFC of our engines roughly, or comparable small automotive diesels?
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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)
(http://home.comcast.net/~vwgtd/tdsae/f53-f57.jpg)
For 4-cyl 1.6lTD motor, see figure 36: (note:bsfc contours range from 264 to 977)
(http://home.comcast.net/~vwgtd/tdsae/f35-f39.jpg)
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.
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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 :) .
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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).
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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.
(http://home.earthlink.net/~rps1976/Images/Diesel/TDI%20Fuel%20Consumption%20Map.jpeg)
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:
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Thanks for the BSFC data, very interesting.
I must say though, that synthetic oil, wheel bearing grease type etc are not worth your while. I have tried such things in the past and never noticed even a .01 mpg difference. If everything spins smooth to the touch and no brakes are dragging severely (which you would smell if it ate any appreciable power), there is not much you can do besides adjustments to the engine itself and perhaps trying to reduce air drag a bit.
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Web
Just because you never noticed a difference in your fuel economy doesn't mean that synthetics don't work. I tracked my mileage very accurately, driving the same route everyday, from home to school, and averaged 38-40 mpg. When I changed to Amsoil gear oil my next tank went up to 42 mpg. There is nothing else I can account for that would have increased my mileage this much. Driving conditions were nearly the same as well. Rammstein will tell you the same thing, he changed his gear oil to Redline and got a 2-3% increase in fuel economy. I do admit using synthetic grease for the wheel bearings won't do much, but every little bit helps and it's easy enough to do.
Peter
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I went from the factory 75W90 to Redline MTL 70W80.
From 3 to 5% difference from last year. :D
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Back when my Rabbit was a daily driver and I was measuring fuel economy on it :lol: I recall switching from 15W40 mineral oil to 5W40 synthetic made a 3% improvement in fuel economy. Furthermore, it was noticeable... especially in cold conditions the engine started easier, and when it ran it just felt "freer" driving on the freeway, etc and just plain had less friction I think and a bit more more torque to boot. Lugging it up a hill I could keep it in gear instead of downshift in some scenarios.
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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).
Although early formulations of syntheitcs may have caused this, it is no longer true (and hasn't been for a long time)... Taken from http://www.mobil1.com/why/myths.jsp :
Myth: Mobil 1 will leak out of the seals of older cars.
Fact: Mobil 1 does not cause leaks. In fact, new Mobil 1 with SuperSyn™ was tested in dozens of industry standard and OEM tests to prove its seal performance. It is fully compatible with the elastomeric materials from which all automotive seals and gaskets are made.
ExxonMobil engineers are wary of conventional oils that tout their use of additional seal-swelling agents. With extended use, these agents can over-soften engine seals, resulting in leaks. More to the point, an oil additive will not rejuvenate worn or damaged seals. The damaged seal may have been caused by a worn rotating metal component in the engine.
If an older engine is in good condition and does not have oil leaks, Mobil 1 with SuperSyn™ provides the same advantages as when used in a new engine. ExxonMobil recommends taking measures to repair the leaks, then using Mobil 1 with SuperSyn™. ExxonMobil also always recommends following the automobile manufacturer's manual for the proper oil to use.
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Just because you never noticed a difference in your fuel economy doesn't mean that synthetics don't work. I tracked my mileage very accurately, driving the same route everyday, from home to school, and averaged 38-40 mpg. When I changed to Amsoil gear oil my next tank went up to 42 mpg.
Right. I have tried everything BUT gear oil and NOTHING made a difference. Now of course it COULD be that gear oil is the ONE area where a decent improvement can be made, but color me skeptical.
Nevertheless, if it was mainly gear oil you were talking about, I stand corrected for now. I still stick with my statement about engine oil and wheel bearing grease though. They just don't make a worthwhile difference whenever I tried anything like that. Of course there IS a very slight difference between old and fresh engine oil (probably more so on a diesel than a gasser), but that's about it.
Marcel
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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).
Although early formulations of syntheitcs may have caused this, it is no longer true (and hasn't been for a long time)...
I happened to me about 6 years ago. It didn't leak until I put synthetic in the engine. And from experience it seems like everytime I use MTL it leaks. I've even had that problem with the seals were replaced.
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If your brother has a 4x4 putting synthetic oil in the diffs, transfer case, and tranmission is supposed to help a fair bit. I have a van that gets 12 MPG so I just don't drive it. It's pretty sad that Ford kept making that crap 6-cylinder for 30 years instead of developing an economical engine and sleeker body like Mercedes did.
My 92 Golf with a low compression (360 psi) engine and bull-low transmission burns 6.3 litres / 100 km or about 38 US MPG running between 110 and 140 km/hr (My speedo is atleast 10% too generous). The engine has 380k km on it and I'm running 0w40 synthetic engine oil and 75w90 semisynthetic gearbox oil. If your brother buys a car with good compression his mileage will go up. The cars with reasonably geared transmissions also get better mileage and don't scream on the highway (bigger tires can help). Also, I wind my car out to red-line in every gear before shifting and can't maintain a constant speed so 38 MPG is pretty good in my book so there's no way your brother can loose money. :P
Cheers, Steve
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I run allotta miles 200km/day - Thurs -Friday - Saint John Sat - Halifax Sat night - Sunday night run back in the night - to Fredericton - and back to the JOB.
Mileage is due to alotta things - including gettin into the pedal - I have run 62 mpg running a NA diesel in 5th around the quebec townships - to 52mpg running with the pedal on the floor on the 20 and 401.
I ran - 480km on 44 liters -30.76 MPG hauling 1000# more stuff and a trailer with 500 pounds of stuff to a market. She ran boost all the time - and I drove her like I was running an old cab over 9000 that I use to drive.
Tall tires - high pressure - low 5th gear - low pinion ratio
and oils all help
Cheers - Centurion
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I just checked my mileage and I'm getting 39 mpg....that sucks. The truck does smoke, so I guess it's just got more fuel than it can burn. I think most of the problem is when I shift it down into 3rd on the freeway to try and keep the speed up around 55-60. The speed limit is 60 most everywhere, so I normally drive in the 65-75 mph if I have a vehicle that will actually do that on a consistant basis. I got it up to 75 once...going downhill....with a tail wind.