86 Carrera gas mileage

I just got back from a trip to Lake Tahoe from Novato and was surprised to get 29mpg on a 372 mile trip using only 12.8 gallons of regular. This was from sea level to over 7000 feet and back.

So, on a tank of gas, I could see 600 miles. Is that possible?

Joe

The 3.2 in that 86 is rated for 22mpg highway. I think you may have a larger tank then you think. I get about 22mpg in my daily drive to work - mostly expressway, very few stops.

Did you drive at like 50mph the whole way? Was there a tailwind in both directions? Were you using an octane booster?

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Mark Szabo
1986 911 Targa 3.2

I averaged about 70-75mph with an eye on the rear view.

The book says I have 21.1 gals capacity. But wait, I once put in 23 gallons when running very empty.

Joe

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[This message has been edited by stlrj (edited 12-15-1999).]

[This message has been edited by stlrj (edited 12-15-1999).]

I get 28MPG when I go to see my parents. They are 300 miles away. I go about 85mph tho.

'85 Carrera

How are you guys calculating your mileage? Are you filling the tank up, then running it down, and filling it up again at the same pump to figure out how many gallons you are using? Are you sure your speedo and odo are accurate? I know that Porsche speedos tend to be pretty optimistic, I wonder if the odos are the same.

28 to 29 mpg at 75 to 85 mph in a car rated at 22 mpg highway seems pretty high to me. I think I get about 14-15 mpg in my SC in mixed driving, and am lucky to break 25 mpg in my 914. Its hard to calculate mpg accurately because you don't really know exactly how much gas you are using and the odo is probably not exactly on, but if you guys are getting anywhere near 29 mpg at 85 mph in a 200 hp car, I'd say that's pretty incredible.

I haven't had my SC for very long but I seem to be average 15-17 mpg in mixed driving.

dave
1981 911sc

I know it's really hard to tell how much gas you use on a 911 because of the bubble under the spare tire. But what I did to eliminate that problem was to add a vent under the spare, so I know that air is not trapped inside instead of gas. And I agree that unless you do this it is impossible to measure your fill up accurately.

I also calibrated my odometer on the highway with the mileage posts as reference. My odo was reading low by 1%.

Joe

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[This message has been edited by stlrj (edited 12-17-1999).]

I average bang on 26mpg in my UK spec 87 Carrera but then a UK gallon is a slightly higher volume than a US gallon (I think).

Hey folks:

To truly measure fuel mileage accurately, you must keep meticulous records.

You should write down the mileage when you fill up, always to the point that the fuel filler clicks off a number of times (it's amazing how much more gasoline will go in after that initial shut-off), and then record how many gallons went in (to the 1/10th of a gallon). Do this a number of tankfuls, and you can then do the arithmatic, and see what your average is. There is no oher way!!!!

Mileage will vary, just like Brian suggested (including temperature, tail-or head-wind, downhill, etc). On my 911SC I can get no better than 20 MPG (US), and I jave been recording mileage since 1982 (evern transposing to metric when the car was in Europe after factory delivery.

Sorry, but I really doubt that any 911 will ever get more than 25 MPG. It's a big engine, it's heavy, and the laws of physics can never be repealed. Tweaked, yes, but repealed, never.....Andras

Well how about my 86 Oldsmobile 98, it's even heavier and has an even bigger 3.8L V6 engine. It gets 28mpg on the hiway, although EPA rated it at 26. I used to get even better gas mileage, like 32mpg, before they oxygenated the gas.

What happened to the law of physics here?

Joe

[This message has been edited by stlrj (edited 12-16-1999).]

This is not your Father's Porsche

I agree. With everyone.

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Mark Szabo
1986 911 Targa 3.2

stlrj:

Right, you MAY get that much. I would be happy to declare the repeal of the laws of physics when: 1. You show me your records which document your milaeage ( I will be happy to send you copies of all the pages of my fill-ups since October 1982 which documents my averages; send me your fax number, please. My fax number is 614.461.6324), and 2. When you can explain how your V8 3.9, which weighs more than the 911, can possibly do that? It does not make sense.

Please, I am not being a wise a**, but somehow claims of extraordinary mileage seem to always have some little left-out bits of information to them. Yes, my log will show that I get 9 MPH at the track, at full throttle, but when the 911 is on the hgihway, at steady cruising speed, it only get 19-20 MPG and there is no way to get better mileage than it gets. You can't get blood from a turnip, and you can't improve the mileage on a corrctly tuned automobile. If you could, you would be rich and famous. There has never been a magic carburator, and I doubt if there is a V8 Olds that get such mileage as you claim. Sorry to be such a skeptic.....Andras

Time out... you can't compare SC and an '86 Carrera gas milage. The SC's CIS (continous, ie bad milage) injection will never get the kind of milage that the Carrera's Motronic injection can provide, especially at cruising speeds. My '79SC averaged 18-20 from California to Minnesota, average speed; 85. I would expect much better from a Carrera.

Sigh....OK time to get serious. Remember, folks, that when an engine burns a shot of fuel/air mixture, it converts energy into heat and pressure. The mechanics in your engine turn this into physical force that through a series of gears and levers puts that force in your tires, which moves the car forward. Pure physics.

The variable we're talking about here is the efficiency that the engine can transfer that energy. A typical gasoline engine gets a fraction of the *potential* energy out of the mix and puts it into the tires - the rest gets shot out your tailpipe as unburned fuel and heat into the cat. I do NOT know the actual percentage - but let's pull one out of the air...say, 50%. I've got a good chance at being close that way

So if your engine burns that mixture at 50% efficiency, half the potential energy gets shot out the rear of the car. If an engine could be coaxed into burning it a little more efficiently, we do some simple math (and I won't here) to figure that the car will use less gas, and move forward the same distance. Hence - miles per gallon. Cars that are "fuel efficient" work this way.

I GUARANTEE you that a car with modern designs to it mechanisms that promote efficiency will get better mileage. So - a 3.8l V8 can TOTALLY use less gasoline for a certain distance, since it's likely more efficient. Like, MUCH more efficient.

But - a 911 was never really designed to be efficient, is it? I have an 86 3.2 Targa. I also have an Escort. Of course the Escort gets better mileage, it's smaller, right? Nope. It just burns fuel more efficiently (and sure, the engine size (1.9l) has something to do with it). I also note that to maintain speed on the highway, I have to use WAY less pedal pressure; the damn thing almost idles at 55.

So sure. An old Olds can use less fuel than the 911, and I guarantee it's not nearly as fun, too.

Conjecture?

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Mark Szabo
1986 911 Targa 3.2

Well, I wish I knew the secrets to increased gas mileage! Like I said, I'm lucky to get 15 mpg overall in my 911SC. Big gas tank, but it sucks it dry at an alarming rate. True, it does have CIS, which is probably not as efficient as Motronic.

But, I checked the on board computer on my Motronic injected 1986 BMW 535i. Similar in engine displacement (3.5) and probably weight (maybe a bit lighter?) to the 3.8 liter, 30 MPG Oldsmobile mentioned above. The computer has not been reset for months, so the computer calculation is based on many tankfuls of gas and many, many miles. Average MPG as shown by the computer: 16.9!

About 6 months ago I ran some very careful calculations on my 914 for gas mileage for some testing I was doing on the effect of Temp Sensor II (the cold air temp sensor). I would top up the tank to the exact same level (with the 914, you can see when the gas tops up in the tank, so its accurate), write down the mileage, drive it until the tank ran almost dry, top it up to the exact same level, and note how many miles were traveled. This is in mixed driving, probably a bit more on the highway than city. I think the best tank I got was a little less than 24 mpg. The worst tank was a little less than 20 mpg. Average was probably about 22 over the course of about 5 months. This is in a perfectly tuned, stock injected 2.0.

Don't know why, but I'm definately doing MUCH worse than the 32 MPG Oldsmobiles and 29 MPG at 80 mph Carreras of the world!

Brian

Brian - your CIS may be out of "tune". They can run rich. If you have the Lambda unit it may have a bad sensor. You should get mid 20's mpg (highway)like all the other thousands of SC's still on the road.
As for this rediculous mileage issue, CIS is a very good simple form of injection but it is not geared toward optimum fuel mileage. A modern pontiac firebird weighs in at around 3500lb with a 315hp V8 and gets nearly 30mpg on the interstate lofting along at 1500rpm in 6th gear. Why? Computerized Tuned Port Injection and lots of sensors. If you want to experience bad mileage slap on a set of webers.

I have a 1983 911 SC and now live in Charlotte, NC. I bought the car when I lived in Long Beach, CA. I have noticed a 3 mpg difference between the non-oxy. fuel in the East and the CA fuel. My SC regularly gets about 22 mpg in mixed highway driving at about70 to 75 pmh. In CA, I rarely broke 20 mpg under ideal conditions.

I am in agreement with the averages for milage here my SC 78 gets at best 13mpg city and 22mpg highway with average speeds 80mph.The motronic cars run leaner and should get better milage than CIS .
Dr. Porsche always touted that his cars were naturally fuel efficient by utilizing light weight materials and engineering techniques it seems you should be able to get decent milage if you can keep your foot out of it which would take much more discipline than I am capable of
One interesting note is I seem to get better milage on premium fuel as to regular

[This message has been edited by jryerson (edited 12-16-1999).]

Andras,

I have a scan tool which allows me to look at the data stream as I drive my 3.8L Olds 98 on the highway and learn about what strategies GM uses to get that kind of mileage. As soon as the computer senses the car is in a highway cruising condition I notice the timing goes up to 50 degrees BTDC and the knock sensor keeps backing it down a few degrees and then back up again, always on the ragged edge of detonation. At the same time the torque converter is locked up and the engine is only turning 2000rpms at 70mph.

I do not think that GM has suspended the laws of physics but is in fact using the laws very effectively and practically.

I also believe that Porsche is using some of these same strategies on the Boxter and the 996 in order to get the kind of mileage they get.

Joe

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[This message has been edited by stlrj (edited 12-17-1999).]

Gentlemen:

I find this thread to be fascinating, and thank you for the additional information on your Olds. Now this makes sense, for my original impression was that you had an older V8, with carburators, with which you claimed to have had such great mileage.

Yes, the more recent 911s will get better mileage, and for all the reasons that everyone cited. And yes, if your V* does all those electronic gymnastics, you will get good mileage.

However, I will still contend that a larger engine pushing a larger car through the air will get less mileage than a smaller car with a smaller engine. There are so many variables (gearing, frontal area, rolling resistance of tires, type of roadway, type of tire, im-tuneor out-of-tune) that an abberation of one car's particulars cannot be used as induction to the general of all cars.

Laws of physics, as we have stated, cannot be suspended - they can be "tweaked" by electoncis/engine management, but if they could be suspended then the touters of high-mileage carburators would be rich and famous by now, not dead and forgotten.

Can we all get along and move on to another topic?...........Andras