60 MPG back to back Thread Secrets Only

Kind of off topic and not. First I have had 60+ tanks back to back. I used to live in the burbs with a nice 40mph 11 mile on way to get anywhere. I think that helped a lot, now that I am "in the city" I have been getting around 50.

Recently, Dec of 10 I had the TB done and now I have noticeably more power, less smoke and lower mpg numbers. I am guessing my last TB was set advanced and this one is probably right on. Anyone think that could make a 3-5 mpg difference? If it is the case I am torn I like the new power but miss the mileage

My best two tanks, back to back, averaged 57.37 mpg driving from Southeast KY to east central Virginia July 9-10-11, 2010 and return. Just me in the car with about 75 pounds of tools in the trunk. I did a variety of driving (stop and go) but the vast majority (97%) was on the road at about 50 mph average, in 5th gear of course. I did run the AC a bit. And, I was not really driving with the attitude to achieve maximum fuel economy.

I apologise flasht, but it seems that just about everything you said on this thread was made up as you were typing it. Why is it that everyone raves about increased economy when doing certain power mods such as larger injectors or nozzles? Obviosly if you limit the fuel being injected into your motor you will go farther with the same quantity. I also disagree with the limiting of air to increase efficiency. It could be done with different ratios, the tune plays a large part as well. In my pd just messing around before I got a tune or boost gauge just driving around the city I averaged 55 mpg to a whole tank. This was with a digi pd set on c. I don't claim to have a complete understanding on the theory of injector size or some of the other stuff you were saying, but I don't think it's cool to talk about stuff that contradicts what seems to be common knowledge or what is considered acceptable to such a large group of semi informed people such as the tdiclub.com.

The general wisdom (which I have no reason to doubt) says that increasing low-end torque is the best way to improve MPG, since it allows you to stay at lower revs for longer (hence decreasing engine resistance).

Certainly, my 115hp PD used to have pretty good MPG compared to most on the forum - it was a Euro model rather than NA, so it had larger injectors & more torque in the map at the low end (both standard). I always found that the best MPG was to be found at the lowest-possible end of the RPM range given the current load.

That's the exact opposite of what flasht was suggesting in his 'mods' post earlier, since his mods would have had the effect of decreasing low-end torque (and also top-end power, but to my mind that is irrelevant to mpg), which would force the driver up into higher RPMs.

MikeMars said:

The general wisdom (which I have no reason to doubt) says that increasing low-end torque is the best way to improve MPG, since it allows you to stay at lower revs for longer (hence decreasing engine resistance).

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Yes, the TDIs are able to burn fuel more efficiently at lower rpms, on the torque peak. An educated view of the BSFC curve will reveal that, so if you increase the torque (within reason and the engines capability), you will increase fuel efficiency at a higher road speed with reduced gearing.

MikeMars said:

I'd say that's a lot more extreme than hypermiling.
Hypermiling costs nothing, and you can do it in any car you happen to be driving. If you normally hypermile, but you need to be somewhere in a hurry, you can just put your foot down, and hey presto! You've got your original performance back.
But if you've strangled your air & fuel intake, spending hundreds in the process (which you probably will never recover), you've permanently blocked off your options, and probably make your car unsaleable (to Joe Public) into the bargain. Once you change your car, you have to start from scratch again.
So to reach the same MPG target, you can either do something free & reversible, or expensive & irreversible. I fail to see the point in spending $300 to save $50/year when vehicles are typically only kept for 3 years.
(Of course, my position is hypocritical since I'm about to have some mild aero parts - exhaust tunnel cover & airflow improvement around the front wheels - added to my car during today's service. It's purely vanity since at $122 they'll probably never save enough fuel to pay for themselves, hence despite adding them to my car I still wouldn't feel justified in recommending the changes to other people. However at least aero improvements don't negatively impact the car in any way, at least, unlike strangling the engine.)

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this was full of funnies.

E-Z Wood said:

I apologise flasht, but it seems that just about everything you said on this thread was made up as you were typing it. Why is it that everyone raves about increased economy when doing certain power mods such as larger injectors or nozzles? Obviosly if you limit the fuel being injected into your motor you will go farther with the same quantity. I also disagree with the limiting of air to increase efficiency. It could be done with different ratios, the tune plays a large part as well. In my pd just messing around before I got a tune or boost gauge just driving around the city I averaged 55 mpg to a whole tank. This was with a digi pd set on c. I don't claim to have a complete understanding on the theory of injector size or some of the other stuff you were saying, but I don't think it's cool to talk about stuff that contradicts what seems to be common knowledge or what is considered acceptable to such a large group of semi informed people such as the tdiclub.com.

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I honestly think that you missed the point that I was trying to make. To be clear though, I was thinking more along the lines of gasoline engines and how they must maintain stoichiometric A/F ratios. This must be done on a gasser motor, and that was why I recommended reducing fuel and air. However, diesels do not have to maintain a certain A/F ratio, so that step may be superfluous in regard to diesels.

Also, it is true that by installing larger injector nozzles, fuel economy will increase due to the shorter injection window. But these benefits, including chip tuning, are marginal. What I preposed was drastic underfueling of the engine which will reduce fuel consumption. Is that really so hard to understand?

FlashT said:

What I preposed was drastic underfueling of the engine which will reduce fuel consumption. Is that really so hard to understand?

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What is hard to understand is the basis for your conclusion. How will underfueling increase mileage? You would certainly reduce power potential, but you are not increasing the efficiency of the engine. To do that without engine modification you need to operate in a more efficient part in the BSFC curve, which is higher load at the torque peak.

UFO said:

What is hard to understand is the basis for your conclusion. How will underfueling increase mileage? You would certainly reduce power potential, but you are not increasing the efficiency of the engine. To do that without engine modification you need to operate in a more efficient part in the BSFC curve, which is higher load at the torque peak.

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Re-read post #28. It really is simple math, the point is to reduce the rate of fuel consumption to the point that the engine is only consuming a specified amount, regardless of rpm's, efficiency, or torque peak. Meaning, if engine load is at 100% and it is only consuming 1 gallon of fuel for XX amount of miles traveled, then you have succeeded. Example: I reduce the rate of fuel delivery to the point that no matter what, I can not get less than say, 60 mpg's on the highway, simply because the engine can not consume any more fuel than that.

I absolutely agree though, it will definately reduce power and efficiency in every aspect, but that was not the point I was making.

Please don't equate thermal energy conversion efficiency with maximum miles per gallon.
That 197g / kWh comes at as near to foot-on-the-floor accelerator pedal position as can be, and 1750 rpm with "WOT" is as near to 48 hp. You CAN'T drive at 1750 rpm and WOT or you'll accelerate and be out of that sweet spot. You can drive at 1750 rpm, and maintain speed, but you'll need only about 8 hp, or about 1/6 of full load. And that's about 300 grams / kwh.
48 hp is about 36 kW. 197 g x 36 kW = 7.1 Kg per hour.
8 hp is about 6 kW. 300g x 6 kW = 1.8 Kg per hour.

Smaller injector flow rates simply extend the fuel flow duration. The amount of power required to move the vehicle through the air at some speed requires some amount of power. Whether that power is delivered in a large squirt over a short time, or a trickle of fuel over a longer time, the result is exactly the same. The same amount of fuel is used to produce the same power requirement.

FlashT said:

Using my method, there really is quite a good bit of room for improvement, especially considering that the average TDI is only at 25-35% engine load when cruising at 55 mph.

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Using your method is a violation of the law. Boyle's specifically. We can add Carnot and Diesel too.
Reducing the power to about 25% without compromising the air mass will entail a variable displacement engine. Leaving one cylinder running at full air volume and shutting off fuel and air to the others will provide one cylinder operating at near to peak thermal efficiency (197 g / kWh) and also reduce the number of kWh. The other three cylinders do have parasitic drag from rings and rod bearings, but the 'spring' action of repeatedly compressing and expanding the entrapped combustion chamber volumes will be less of a loss than using them to pump air.

My Saturn TDI project has been topping 60 mpg over the last few weeks as the weather has improved. My commute is mostly highway, staying around 60-65 mph most of the time, coasting to exits, toll plazas, stop signs, ect. My best so far has been 64 mpg, the last two tanks have returned 63 mpg.

The car weighs 2480 lbs with 10 gallons and a second battery in the trunk, has a '97 AHU with a RC2, no muffler, and a VR6 clutch. I've been experimenting with aerodynamics as well...making one change at a time and measuring results, a lot of little things can really add up.

Lug_Nut said:

Please don't equate thermal energy conversion efficiency with maximum miles per gallon.
That 197g / kWh comes at as near to foot-on-the-floor accelerator pedal position as can be, and 1750 rpm with "WOT" is as near to 48 hp. You CAN'T drive at 1750 rpm and WOT or you'll accelerate and be out of that sweet spot. You can drive at 1750 rpm, and maintain speed, but you'll need only about 8 hp, or about 1/6 of full load. And that's about 300 grams / kwh.
48 hp is about 36 kW. 197 g x 36 kW = 7.1 Kg per hour.
8 hp is about 6 kW. 300g x 6 kW = 1.8 Kg per hour.

Smaller injector flow rates simply extend the fuel flow duration. The amount of power required to move the vehicle through the air at some speed requires some amount of power. Whether that power is delivered in a large squirt over a short time, or a trickle of fuel over a longer time, the result is exactly the same. The same amount of fuel is used to produce the same power requirement.

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But what if fuel delivery is limited by using a smaller sending unit? That would allow you to use larger injector nozzles. The whole point of my reasoning is to limit fuel consumption based on liters per hour. If you can limit that, then you can still attain a useable cruising speed, but the rate of acceleration will be reduced, since less power is available. In turn, better fuel economy numbers should be attainable.

And the thing about power requirements, you would need less power to accelerate at a slower rate, and even less power to maintain a constant speed, so therefore, you would simply need to figure out the minimum fuel consumption rate to maintain a certain speed. That is the limit without modifications.

I'm sorry flasht, that just makes no sense at all. All you have to do to restrict fuel intake on a diesel is not to use your right foot. Strangling the amount of fuel which is injected per cycle will not magically make it able to use less fuel to reach the same speed, it will almost certainly make it *less* efficient because the driver is forced to use a higher rpm to get the same fuel delivery.

MikeMars said:

I'm sorry flasht, that just makes no sense at all. All you have to do to restrict fuel intake on a diesel is not to use your right foot. Strangling the amount of fuel which is injected per cycle will not magically make it able to use less fuel to reach the same speed, it will almost certainly make it *less* efficient because the driver is forced to use a higher rpm to get the same fuel delivery.

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In manual transmission equipped vehicles, the gear ratios are fixed, so how could the engine possibly use 'higher rpm' to go the same speed? The only different thing that happens is that you accerate at a slower rate, becuase there is less power available.

Firstly, try actually reading the line that you've highlighted.

... because the driver is forced to use a higher rpm ...

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... In manual transmission equipped vehicles, the gear ratios are fixed, so how could the engine possibly use 'higher rpm' to go the same speed? The ...

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Easy. The driver finds that the car can't get up the hill/maintain speed/etc in the current gear, and drops down a gear. This increases the RPM, and hence the number of fuel injection cycles, and hence the driver gains the intended power.

But since the engine is spinning at a higher RPM (due to being in a lower gear), it's using more fuel than it would have been otherwise, to maintain the same speed.

... you accerate at a slower rate, becuase there is less power available

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And I still think the best way to obtain this is simply not to press your right foot so hard.

Lug_Nut said:

Oh,
1996 Passat sedan, I think I had a 1k ohm Evry mod on it at that time.
Moderately hard acceleration (no wheelspin) up to desired speed, then highest gear possible (1200 rpm in 5th and 35 mph) and no acceleration. Maintenance of momentum with minimal braking and slowing, and minimal acceleration.
Central Massachusetts, between 1200 ft and sea level, May 5th to May 12th and then August 6th to August 16th of 1999.
Mileage was from odometer (checked against 100 consecutive miles of interstate back in '97? or '98?) and dollars spent over price per gallon ($16.75 at $.999 a gallon is 16.76676 gallons).

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oh boy - great mileage. I guess I have to take some mileage lessons. I couldn't achieve this on my 6 speed 02 Jetta. It is inspiring - Thank you.

Lug_Nut said:

Oh,
1996 Passat sedan, I think I had a 1k ohm Evry mod on it at that time.
Moderately hard acceleration (no wheelspin) up to desired speed, then highest gear possible (1200 rpm in 5th and 35 mph) and no acceleration. Maintenance of momentum with minimal braking and slowing, and minimal acceleration.
Central Massachusetts, between 1200 ft and sea level, May 5th to May 12th and then August 6th to August 16th of 1999.
Mileage was from odometer (checked against 100 consecutive miles of interstate back in '97? or '98?) and dollars spent over price per gallon ($16.75 at $.999 a gallon is 16.76676 gallons).

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oh boy - great mileage. I guess I have to take some mileage lessons. I couldn't achieve this on my 6 speed 02 Jetta. It is inspiring - Thank you.

FlashT said:

Fuel Economy: who cares? hammer down!

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Yep, we should listen to you for fuel economy advice...

SMALLER nozzles will atomize the fuel better leading to quicker, and to more complete, combustion. Larger nozzles increase the rate of fuel flow, but since the pump or injector is determining the quantity of fuel to be injected, a faster flow capacity only lets that same volume of fuel get in within a shorter time.
Large orifice tips and low flow (your fictitious smaller sending unit) will lead to less complete combustion of that volume of fuel, possible fuel migration past the rings and oil dilution.
It is all to do with the fuel droplet surface area and it's exposure to the O2 in the compressed and heated air.

What you proposed, less air (restricted air flow)and bigger fuel droplets (bigger injector tips), are exactly opposite the conditions needed for fuel efficiency (whether thermal or mpg).

The simplest means of limiting fuel delivery volume is to put a rock under the accelerator pedal.

^ well put, Lug.

Seems as though no one has mentioned to flashT yet that our engines run LEAN, all the time (with full WOT the only possible exception to this description of A/F ratio.. even so, stock tuning is above stoich at WOT to avoid smoke).

With a constant surplus of air to combust with, the power produced is dictated solely by the quantity of fuel injected. Since cruising at a constant speed requires a constant power (suppose 60 mph = 15 HP required to overcome aero and rolling losses), then you will ALWAYS need the same amount of fuel to maintain the same speed, all other thing constant.

If you study the BSFC chart posted previously, you'll see that gearing changes can move the engine rpm and thus fuel conversion efficiency around. Similarly noticeable, but small, gains can be had from improving combustion efficiency, from nozzle size / atomization or injection timing - but this is a very limited opportunity because the stock components and tuning are already really quite good.

So the biggest gains in mpg are really found from reducing aero and rolling load (aeromodding, LRR tires, etc), or slowing down, which naturally reduces both. Hypermiling techniques break the mold somewhat and can be both very effective and very dangerous, depending on the degree and specific methods employed.

However I continue to remain amazed at how many people on this site over-analyze every facet of engine maintenance and other variables for effect on mpg, but so few actually just try aero-modding their vehicles. I'll take this opportunity to again point out that I raised my hwy mpg from 47 to 56 mpg at ~75mph continuous hwy cruising, almost all from reducing aerodynamic drag. Simple.

I pretty much agree with every part of your post. Virtually every time someone comes on here complaining about poor MPG, they talk about faults / mods etc in their first post, without looking at the conditions & their driving style. It's only when people interrogate them that we find out that they're doing short trips in the city, or it's -20c, or they like doing 85mph, or whatever.


When it comes to mods, I tend to look first at the cost versus benefit. There are very few mods which save enough fuel to quickly repay the cost (especially if you have to rely on a garage to do the labour).

FlashT said:

In manual transmission equipped vehicles, the gear ratios are fixed, so how could the engine possibly use 'higher rpm' to go the same speed? The only different thing that happens is that you accerate at a slower rate, becuase there is less power available.

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Use a lower gear? Really, get your feet on the ground.

Lug_Nut said:

Yep, we should listen to you for fuel economy advice...

SMALLER nozzles will atomize the fuel better leading to quicker, and to more complete, combustion. Larger nozzles increase the rate of fuel flow, but since the pump or injector is determining the quantity of fuel to be injected, a faster flow capacity only lets that same volume of fuel get in within a shorter time.
Large orifice tips and low flow (your fictitious smaller sending unit) will lead to less complete combustion of that volume of fuel, possible fuel migration past the rings and oil dilution.
It is all to do with the fuel droplet surface area and it's exposure to the O2 in the compressed and heated air.

What you proposed, less air (restricted air flow)and bigger fuel droplets (bigger injector tips), are exactly opposite the conditions needed for fuel efficiency (whether thermal or mpg).

The simplest means of limiting fuel delivery volume is to put a rock under the accelerator pedal.

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Thing is, I never said anyone should listen to me. To be perfectly clear: No one should implement the ideas that I proposed. I was just testing a theory of mine, wondering if might be feasible in the real world. To be honest, I am really not that concerned with FE since my car is more modified for the track than for FE. I don't even drive 10K miles in a year, so whether or not I am getting more than my 40 mpg average is irrelevant to me.

Easy flash, if all this was your theory, you should have proposed it as a question rather than present it as fact to where someone with less knowledge might believe it. There is no need to be upset over this. Just express the intent of your posts better, and you will be better understood, or people will explain it the way it Is if you are incorrect.

E-Z Wood said:

Easy flash, if all this was your theory, you should have proposed it as a question rather than present it as fact to where someone with less knowledge might believe it. There is no need to be upset over this. Just express the intent of your posts better, and you will be better understood, or people will explain it the way it Is if you are incorrect.

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That was, in fact, precisely what I wanted.

Lol, hey you know Malone is offering a stage 0 tune. Natural aspiration!

However I continue to remain amazed at how many people on this site over-analyze every facet of engine maintenance and other variables for effect on mpg, but so few actually just try aero-modding their vehicles. I'll take this opportunity to again point out that I raised my hwy mpg from 47 to 56 mpg at ~75mph continuous hwy cruising, almost all from reducing aerodynamic drag. Simple.

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Aero modding is on my list, along with the .658 5th gear. Cruising the flats of SE MI and Ohio, friction is the main enemy. I did manage to get a 1000 mile tank (in a wagon!) but it took more effort than I can muster routinely. And still I didn't quite break 60 mpg.

I also loved the look of your car when it was lowered. Presumably that helped aero performance somewhat, at the expense of scraping on these wonderful Michigan roads?

MikeMars said:

The general wisdom (which I have no reason to doubt) says that increasing low-end torque is the best way to improve MPG, since it allows you to stay at lower revs for longer (hence decreasing engine resistance).

Certainly, my 115hp PD used to have pretty good MPG compared to most on the forum - it was a Euro model rather than NA, so it had larger injectors & more torque in the map at the low end (both standard). I always found that the best MPG was to be found at the lowest-possible end of the RPM range given the current load.

That's the exact opposite of what flasht was suggesting in his 'mods' post earlier, since his mods would have had the effect of decreasing low-end torque (and also top-end power, but to my mind that is irrelevant to mpg), which would force the driver up into higher RPMs.

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Well explained and sensible input.....

Should be lot's of you guys doing the 60-60-60 backto back thingy now with the nice warm weather. I'm able to manage it again with the same driving technic's as before ..... summer fuel, summer air, and warmed lube from the get go makes it all come together. June through sept is the only time I can do this?

Question to all you guys getting high MPGs, is your odometer correct? As I am sure you all know, changing tire size will affect the actual miles being rolled up......could over state or under state, depending on the tire size deviation from OEM. Also, even the OEM tire size doesn't always result in accurate odometer readings!

Just wondering! In my Excel spreadsheet formula(s), I add a correction factor depending on the circumstances,,,,,take off a little or add a little! Of course, the variation has never been more than 1.5% + or - !