Turbocharged Saab hit 99.9 Mpg highway, 51 Avg after fill.
 

Well, for those who thought you needed a naturally aspirated or electric assist engine to achieve unheard of mileage, think again!

Vehicle: 1998 Saab 900 S 2.0L Turbo 5 Speed Coupe.
MPG Modifications: Gutted interior, only 2 front seats (reduced overall weight by about 200lbs. Hi-flo filter + intake located right next to the engine (gets crazy hot.)

Trip: Belleville, NJ --> Pittsfield, NY = 180 miles each way over mountainous terrain.
Conditions: High humidity, partly cloudy in the low 80's.
Fuel: BP Ultimate (93+ octane rating on pump.)
Techniques employed:
- Acceleration on boost gauge remaining in -10 in/hg of vacuum. (gently depressing 50% throttle max.)
- Speeds not exceeding 65 mph using throttle. (GPS said 61, Speedometer said 63 typically.)
- Drafting behind large vehicles where roadway was full of cars... (never do this on the open road)
- Engine off neutral coasting down every incline. (Speeds vary, please be aware of local laws and speed limits.. lets just say "I got really far" after many of the hills with the engine still off. Vehicle brakes do not work with the engine off, keep this in mind if you are doing this at highway speeds. Simply let out the clutch to restart the car in 5'th gear once speed reduced to below 55 mph.)
- Neutral coasting during in town driving (it's much easier to maintain slow rolling speeds due to less wind resistance.)
- Always parked facing next direction of travel. (avoid unnecessary back-ups and turn around)
Luck factor: There was virtually no stops or traffic in front of me for at least 350 miles of my total trip. I chose good times to travel, and misses traffic on purpose.

It took 2.5 hours of constant downhill coasts I watched the MPG gauge go from the high 50's to the mid 70's for a while. Finally at the bottom of a hill it had maxed out at 99.9 mpg where it remained for the next 30 minutes before it's descent back down to earth at around 35 mpg (construction zones and traffic forced me to slow down out of my "sweet spot."

Stopped at the BP gas pump I had used to fill before leaving, mileage was reset to 0. Upon arrival it was 410 miles, the tank took 8 gallons of gas to fill back up. = 51.25 avg / mpg tank.

The plan for this vehicle was to be fun to drive and perform double duty as my race car, and gas mileage experiment. While some may argue burning up gas for fun at the racetrack negates all fuel savings, I tend to disagree. I find saving fuel to be a great challenge and equally as satisfying as running 13 seconds in the 1/4 mile or running a road course. The benefits of this vehicle aren't in the dollars saved, if money were my main concern.. I wouldn't drive an automobile. My Saab just goes to show "it can be done." You can have a fast / fun car that also sips fuel when off boost to the point that hybrid owners may be envious of.

I have recently purchased a laptop and run a program which basically controls all parameters of the ECU and how it operates the vehicle's engine. I'm working on several new maps, some for increased hp and performance, and some for ultimate fuel conservation. There's a fine line between sipping fuel and pre-detonation when it comes to turbocharged engines though. When reducing the amount of fuel going into the engine, one must also reduce the throttle input to match, or risk catastrophic engine failure.

This, my friends.. is my eco-modding story.

http://i16.photobucket.com/albums/b3...d/100_0621.jpg

(The top row of pixels are out on my information display, but you can see for yourself.)

This is so far beyond what would be expected from the above vehicle with the above techniques that I must doubt the accuracy of your measuring techniques. 99mpg is an obviously erroneous figure. Even the 50mpg fill is suspect. Can you do two 50mpg tanks in a row?

I typically get in the mid 40's with mixed city / highway. The key to my success here has everything to do with a low compression engine staying out of boost, and spending just as much time coasting with the engine off, as I do with the engine on. 51 mpg is my record high for this car, last fill was 359 miles / 8.119 gallons of fuel = 44.21 mpg. Prior to that was 423 miles / 11 gallons of fuel = 38.45 mpg.

I take trips upstate NY every few weeks, so of course I will report back next time I return home with new results. I believe If traffic conditions remain the same, I could potentially pull of another 50 tank.

The common misconception most people seem to have is that if you have a turbocharger, you can't get good gas mileage. When in fact, turbocharged engines are more economical off-boost in most cases. 8.4:1 compression requires much less fuel consumption than my Subaru with 9.5:1 naturally aspirated.

Staying out of boost is as simple as not going more than 40% throttle in the first 2 gears, and less than 50% throttle in 3-5 gears. In essence, when I'm driving for fuel conservation, I'm driving only as though the engine were naturally aspirated. I let the 5 speed transmission gearing do the uphill work for me by downshifting to 4'th gear keeping the rpms at 2,600 where this engine makes peak torque - but I stay out of boost as I try to never exceed 10 in/hg of vacuum. At 65 mph on the highway the engine is very near peak efficiency from what I've observed thus far from my records.

The vehicles mpg calculation is not an instant reading, it doesn't fluctuate quickly at all, it climbs very slowly. On this particular occasion I was able to coast for a few miles at a time many times in a row as I rolled through the mountains.. climbing back up-hills was a breeze achieved by my downhill speeds. Now, if one were to discredit the factory gauge reading and call it instant, regardless of any error.. the final fill / math shows that at over 50 mpg the car was getting plenty of time with infinite mileage as I coasted with the engine off.

There are a few things worth noting here.

Smaller turbocharged engine are definitely more efficient than larger engines, even when on boost in certain circumstances. It just mainly depends on if you hit fuel enrichment under boost or not and if the engine has to pull ignition timing back. However, the 2.0L isn't a small engine to start with for a car of that size. If you look at the EPA ratings for the 2.0L turbo and 2.0L NA, the NA gets better mileage as would be expected.

A lower compression ratio engine is generally less efficient. You can't compare an AWD car to a FWD car, theres more losses in the AWD due to the drivetrain.

I'm as doubtful as robertsmalls here. My guess would be either you had a good amount of downhill coasting (and the trip back would be much lower), or you had a short fill, or both. I'm not trying to rain on your parade, but that vehicle at that speed just doesn't equal that mileage.

Good job getting 50 mpg. I might suggest running low octane fuel since you are still operating in the intake vacuum side of things.

I'm not sure what a short fill means, but I went from a full tank / 0 miles on the trip OD to filling until the pump clicked off. After squeezing another dollar into it filling it to the brim, you could consider it about 8.4 gallons which would still equate to 48.80 mpg.

I assure you there's no smoke & mirrors. This has everything to do with the driving techniques here and my relationship with my automobiles. Quite frankly, I hoped to use less gas than I did. I achieved a high of 47 mpg in my dodge Neon with 160,000 miles, about 37 in my Subaru Legacy with 204,000 miles..... so my Saab which tips the scales at 2,700 lbs getting as high as it did really isn't as difficult as it sounds. Each way on the trip was roughly 180 miles, I had the engine off for an estimated 40 miles each way as I rolled down hills effortlessly (and up and over the next one fairly quickly with the speeds I obtained going down hill. Out of my 410 miles, perhaps 70-80 of them were with the engine not running at all. The rest were at (what I call) peak engine performance. 410 -70 = 340. 340 / 8g = 42.5mpg. That ought to help put it in perspective a bit. Free mileage = outstanding numbers. I believe anybody can do it, I'm no pioneer just love to experiment.

Any other theories on why / how I may have miscalculated or what could potentially have skewed my results? I'm always eager to take on other perspectives. Thanks

I believe his figures are possible.

Nice work Drive Stick.

His car has fairly good aero and he is using the terrain to his advantge very well.

Especailly if his gearing is allowing him to use lower revs to maintain speed.

Reducing his vehicles weight also allows him to use less energy to climb, as well as less sectional density on the downhill sections which would reduce his terminal downhill speed.

regards
Mech

current or avg?
 

My wife's bone stock 2010 equinox very often shows 99.0 mpg on the instantanious mpg readout. No big trick--get to speed , let off the gas. A long downhill coast would keep it there a good long time.

I have not been able to get a trip average mpg any where near the 50's. You are to be congratulated:thumbup:

Coasting down and building speed for the next uphill run is the way to do it for the best mileage. Most use their cruise control which does just the opposite....

I do find it hilarious when someone tells of success that there are 10 people waiting in line to tell him that he mis-filled his car, that he had wind at his back, he didn't do aba testing, the 3 or more tanks that he filled were all short? and didn't give true results. It is quite frustrating. If he is in a hilly or mountainous terrain, getting double the EPA rating is fairly easy. Plenty of people are getting 25-30% better on flat terrain. Believe what you want, but you dont need to always call BS to feel important.

What exactly do you teach?

I find one-run fe claims hilarious.

What do they mean?

See "Sport Coupe" as exhibit A. Coupe's numbers are not fake... but you can be damn sure the whole gaslog average fe is nowhere near that of the particular "snapshot" I have here, for the reasons you derisively listed above and even more.

Nice result !

They either give instant FC, or a tank average FC.
Then again, even instant FC is usually slowed down slightly - by a few seconds - to keep it from changing constantly.

The Scangauge reading is closer to being instantly, it's at 0 L/HK some 5 seconds before my car's FC reading goes to 0.

Thank you to those in support of great gas mileage, I appreciate it. The cars gauge does tank AVG, which is why it was shocking to see it reach 99.9 but that was after back to back to back downhill coasting engine off.

I was excited about the fact that I was finally able to see the driving habits at work with this car. My other vehicles don't have any such OEM equipment to help me read things. (also installed aftermarket vacuum/boost gauge in this one.)

Everyone gets "unlimited" gas mileage when coasting with the engine off, and most of us get in the 20's / 30's around town so I don't know why it's hard to believe that some of the time we are actually getting 99.9mpg. That's how the overall tank numbers raise significantly, by having high highs, and not so low lows. Everyone's car does this under the right conditions.

Frank Lee - people don't make posts about every tank they get good results from. They post when they get outstanding results, or something note worthy to encourage the fellow board members. I want people to know anything is possible. I can see why you might say: because quite Frank-Lee... it's funny how people drive long distances remaining on the gas pedal the entire time. They could be using advanced driving techniques and reaping the benefits of saving some at the pump. ;)

I feel I should comment on this thread..

I've just bought a saab similar to the one the OP is discussing.

A couple of observations/points to make

1. The SID (onboard computer) offers BOTH Average and instant MPG

2. Even the 185bhp engines have a compression ratio of 8.8:1 (not particularly low for a turbo engine, infact similar to the m20 6pot 12v NA lump in my old BMW's)

3.I dont believe the OP is claiming that his FE figure is representative-merely reporting his findings on this ONE trip.

4. I'm currently baselining my car, and hope to have a figure available within the next week- currently its looking like 40mpg UK (33mpg US) with no EOC.

Certainly, its worth taking all figures published with a pinch of salt, but there will never be a shift in attitude of the general public if us ecomodders cant support each other!

Thankfully the OP is not selling a "Snake oil" additive etc.

They are possible in that car, but not at 65mph average. At 65mph, it takes far more energy per mile to drive a Saab through the air.

Using P&G, operating the engine near peak BSFC or not at all, I was able to achieve almost 50mpg in my Subaru Legacy on ideal terrain - at 35mph.

DriveStick - the techniques you use do save fuel, and your Saab has pretty good aerodynamics. I'm sure you got pretty good mileage, but I would expect something in the low 30's with cruise control, low 40's with the P&G that you used. I have to admit a lightened Saab is better configured for this sort of driving than I had realized, for the reasons OldMechanic mentioned.

Fuel pumps are known to deliver inconsistent fills (just ask anyone at a fuel economy run), and extraordinary claims require extraordinarily careful data gathering.

So for now, congratulations on what is in any case an impressive result. Now let's wait and see if your next fill comes up long.

I believe you are misreading the sentiment here. The "naysayers" as you would have them are known, reputable, frequent posters. They (we) are here not just to pat each other on the back, but to make sure everything we do that for is replicable and worth that pat. Having been around here for a while, I would encourage you to trust that RobertSmalls, Daox, Frank Lee, et al are KNOWsayers, not naysayers... plus a little bit of venom as always from Frank ;).

I'd be willing to believe this number is achievable with this car, because it does have reasonably good aero, but I doubt you could keep doing this trip. I also believe you had ideal conditions for this tank. My friend has an 01 9-3, which I would consider VERY similar to your car. I have driven this car. I do well in fuel economy competitions if I might say so, and getting this kind of mileage from a saab like yours is tiresome without mods, and I would add doubtful at the speeds you mentioned - as you said, it's much easier to coast in slower speeds. Like I said, I don't not believe you, but I too think you had some pretty ideal conditions, and doubt the duplicability of this tank. Aerodynamic modifications would help not only your time at the track, but the ease of consistently getting numbers in the 50s. Although it's exciting to get a one-off tank with very good numbers, I feel that's not what we're really after here. I think the real purpose behind the forum is CONSISTENTLY good mileage; reporting whatever mods/techniques used for others to try out and keep pushing the MPG envelope. Don't take it as us shooting you down, take it as encouragement to continue testing and give a good solid raising of the bar for other saab owners to aspire to and try to get even better.

No doubt about it, some areo mods would keep figures like this possible on long trips. The conditions were perfect, no traffic, no wind, no obstacles, and a LOT of huge hills. Up-hill climbs were in the 50-55 mph range, and steady flat driving was 61-63. Downhill coasts obtained speed which I can not mention. The momentum kept me going much further than if I had used the brakes and maintained a legal speed limit down hills.

(I do not condone breaking laws, as always with no risk there is no reward.)

Getting this kinda mpg from this vehicle (or any) is only possible under the same circumstances. That much is certainly true. Results will always vary, to what degree I don't know. I will definitely record my results next time I go upstate and back to compare.

Next time I go, I will probably have more hp and more weight reduction - but don't let that confuse you. Results only depend on how the vehicle is driven and the outside conditions.

Ya think? :thumbup: Nice numbers, thanks for sharing them. I want to move where the roads are that uncongested!

Note that I didn't go after the OP...

On an instant reading, surely, but not on a tank average reading.

While coasting engine-off, metric format is a better indicator as it'd show 0 L/100 km.
But when stopped, it should read infinite ...
MPG is quite the opposite, it'd show an infinite reading during coasting, with 0mpg while stopped.

Neither of the infinite values can be used to calculate averages ...

It's also the theory behing P+G .

Let's say you were getting 50mpg before starting the coastdown.
You'd need to travel an equally long distance with the engine off to reach 100mpg - and more coasting downhill to go beyond it.


Maybe the trip computer is using some very high (near-infinite) instant mpg values while you're coasting engine-off , and these may throw off the overall average reading ...

Technically it's correct to use the extremely high mpg figures, but in the real world it doesn't work out that way in the end :D

51 MPG unassisted is pretty high for that car on the freeway even at the speeds listed. I suspect the drafting may have played a big part. Warm air into the engine certainly helps too.

BTW, I'm 450 miles into a 48+ MPG (indicated) tank myself. 100% slow speed city driving with traffic lights! As long as I stay away from China it should be my best tank ever.

Frank,
I teach high school technology education in the areas of metals and automotives. I also tend to teach realism, acceptance, patience, politeness, and other lost arts of humanity. Some of these are lacking in many of the threads. If you would like to question the validity of my teaching degree or the magnitude of my brain power (and its possible battle for supremacy over room temperature), go ahead. I would suspect that this would be par for the course. I maybe should start it in another thread as "I am a teacher" to which many can tell me how that isn't possible, how I have mental handicaps, or how I must be a preschool teacher (as first graders appear to be more intelligent). I have no idea on whether I should leave this forum all together or stay so that there is a balance in this microcosm that is ecomodder.

It looks like you still have a bit left to learn.

This is the best / funniest thing I've ever read, and I've read some pretty great books! haha Thanks for lightening the mood, I appreciate it.

When all is said and done, I say just take what people say for what it's worth. When I receive positive feedback, it encourages me to continually strive for better results. When people doubt the factual material I present them, I smile and say to myself "everyone is entitled to their own opinion."

In this case, I completely understand how it might be hard to believe in my results. They were difficult to achieve and conditions may not present themselves to be so ideal again. The human variable in the equation is really the limiting factor in most vehicles. People may consider themselves great drivers, savvy hypermilers, but in reality somebody else can always do it better. If people can't duplicate what somebody else did.. their reaction is to say "it's impossible" or "highly unlikely." I accept this as human nature. I can't jump 4 feet off the ground, but I still believe Mugsy Boughes @ 5'-3" did.

Perhaps my lack of contribution to this forum has lead some to believe I am not a significant part of the community. Well, that's because I work 3 jobs.. am in the process of designing / building a net-zero energy house in NY and have been working on design and theory for my boattail saab project. Guess I'm just usually too pre-occupied to post on forums. I prefer to post when something significant happens.
:thumbup:

http://i16.photobucket.com/albums/b3...peed/ffsff.jpg

I'll be back when this is done, of course.

Then I would assume you know the rules of a civilized debate.

In case you forgot.

State your position clearly and succinctly.

Do not attack or denigrate your opposition.

Your grade so far is not worth mentioning.

regards
Mech

I believe you posted them in good faith - though I suspect the numbers were off because of the infinite-mpg error while coasting engine-off for an extended period.

We call them passive houses over here, I'm looking into building one as well ;)


It reminded me of the older Saabs (99 ?) and the SAAB 92 prototype (1947)
http://ll.speedhunters.com/u/f/eagam...news/saab3.jpg

If you look carefully at the road ahead in the photo, you will see a hyper milers dream, almost the perfect grade conditions to allow pulse and glide while maintaining a fairly constant speed. Apparently some of the grades were steep enough that he could gain speed downhill and use that to climb some of the uphill slope beyond.

Combine that with drafting opportunities and you have the ingredients for success.

That prototype Model 92 Saab is one I don't think I have ever seen before, and one of the best designs aesthetically I think I have ever seen.

regards
Mech

I love that prototype, I was inspired in part by the fact that almost all saab vehicles have quite a nice slope to the rear window! Very cool photo you posted there.

The Passive Haus concept is something I was reading about, so yes essentially net-zero / passive haus techniques are very similar. The two books I read most recently were:

- Green From The Ground Up
- Toward A Zero Energy Home

By: David Johnston & Scott Gibson

Great reads, kinda the same book.. but one covers houses which employ the techniques for producing their own energy and being self sufficient, and the other talks about the different systems in a bit more detail.

For your engine off coasts down hill what are you doing to take care of your turbo? What I mean is those things get hot while compressing air, and spinning at high RPM and flowing lots of hot exhaust gasses. Then with the engine off for coasting the oil lubricating and cooling the bearings stops flowing and starts to cook off in the high temp of the turbo.

Even if he short filled a whole gallon he is still in the 45mpg range. After a few more tankfulls we may know better how well a saab turbo does.

You are correct, turbocharged vehicles should be allowed to run for a couple minutes before being shut down in order to avoid coking. (For those who aren't yet familiar with coking.. basically the oil that sits in a turbochargers oil passage around the bearings essentially "cooks" in place as the turbo cools down.)

On this particular vehicle, the turbo oil return line comes directly off the bottom center of the cartridge. This allows just about all of the oil to drain-back to the oil pan. Since the drain line is only about 3 inches in length, and sits a mere inch above the standing oil in the oil pan it does a great job at draining itself before much coking can occur.

The turbo is the original T25 with 130K miles on it so far. A look inside didn't reveal any crude build-up when I changed the drain line. I don't really cool it down when the turn the car off either. Partially because it's got 130K miles and partially because it's done so well thus far I guess the engineers did a good job setting up the lubrication system.

Engine off coasting / shut downs with out cool down are relatively the same minus the engine turning back on after coasting (usually no more than 2-3 minutes at a time) the oil doesn't seem to get a chance to bake in there as the hot oil resuming flow would push any buildup right out. (this is my theory anyway.)

I think a lot of that "coking" cool-down theory is for the worst-case scenario ie. racing, hard-working heavy equipment, etc. and probably not needed for garden variety street driven stuff.

With gentle driving, it is less of an issue. Good quality oils (especially good synthetics) with good heat tolerance reduce the issue further.

U don't run low octane in turbo motors or any forced induction motors for that point It would ruin the turbo after a while

I'm not sure who told you this, but I'll tell you the reason turbocharged or high compression engines use higher octane gasoline.

The turbocharger sees no gas, it's predetonation you're trying to avoid with the higher octane rating. I would take the time to explain what detonating is, or how octane ratings work but.. I must go to work.

I don't think he ran any boost. I believe he kept the engine at 10"hg vacuum.

Part of being eco in my opinion is to not use the more highly processed fuel. When the lower octane will run the engine without detonation. He was keeping his cylinder pressure down with his driving style.

I have had a turbo truck. The manufacturer recommended premium fuel but stated it was safe with lower octane as the fuel map and boost and or timing would adjust to prevent engine knock. I never drove it for economy. It had a turbo and I was going to use it. In my part of the country premium fuel is not always available. I had to fill with unleaded regular or gasohol many times.

Cool graphic showing the extended butt of the Saab.

Are they out of business after the GM collapse?

I picked one of these cars up. Just got 32.6 mpg in hilly terrain by staying out of the boost averaging about 65mph. Not bad for a $400 car with 178k miles and a bad o2 sensor. They published a max economy rating around 45 mpg @ 45 mph back when they first came out. Since then Saab made some minor mods for the Talladega record to reduce drag (ie. dish like wheels and ride height) . These cars will do 150mph+. I will post more results as I get this thing tuned up.

I had a reading of -39mpg on my SG2 today.

Driving backwards? :p

I payed a little more for this car than you did for your SG2. I will recoup my investment vs driving my Tacoma in about 6 months. What do you tow your boat with?

ok so i"m a little late to the party (story of my life!).
having owned a ng900 saab i can tell you from my personal experience that the SID (SAAB Information Display) on the dash takes quite a bit of time (and/or different driving style) to make a change in the mpg number.
I say great job even if you can't make it happen everyday.
***a side note about my experience with switching to synthetic fluids, I saw a 1.2 mpg increase in the MPG #'s after switching to synthetics (it took about a month to get there but it stayed there for the following 8 months i owned the car, so probably not a fluke.