most fuel efficient 911
 

Hi,

I have a 1967 911 with the smallest 911 engine but 48 year old technology. How would the mpg compare with a larger engine with the newest technology. In other words, which 911 gets the highest mpg at a steady speed on the highway.?

Thank You,
Mike

I only worry about Smiles per gallon. :)

I just noticed this was your first post, please post a photo of your car.
It is an unwritten rule... :)

A '78 SC is not a gas sipper.

I programmed an open loop lean burn chip for my completely stock '86 3.2 and cross country at an average of 80 mpg was getting almost 700 miles/tankful.

My 3.2 gets around 34 miles to the gallon (UK gallon) on the open roads here in New Zealand at around 100kph (the speed limit) When I'm being naughty it's much lower, but that's why you own an air-cooled 911!

Excellent! For those unaware, it should be noted though a UK gallon is 1.2 US gallons ;)

You're doing something wrong if you are getting that sort of fuel economy.

Could you explain this a bit more?

I would also like to know more about the details at 675 miles on 16.5 gallons - over 40MPG?

oops wrong tank size - looks more like 675 mile of 21 gallons so 32 ish ?


To answer the original question, I think the 3.2 will get you the best gas milage. I watch my fuel milage pretty closely and I used to get 28 mpg on a trip with my stock 3.2 on regular gas. My 92 C2 gets 23-24 mpg on a trip and requires premium gas however I just got 26.5 from Virginia to NY recently - 412 miles on 15.5 gallons. My county sells only 10% alcohol fuel so I am wondering if the increase was due to filling up in Richmond and the fuel possibly not having 10 % alcohol.

oops found this for 3.2
MPG City 16
MPG Highway 23
MPG Combined 19
Fuel Tank Capacity 22.5 U.S. gallons

In answer to the original question I believe the newer the car, the better it's "theoretical" mileage. According to what I've read the later injection systems are more economical than both the earlier systems and carbureted versions. Makes sense since the systems are able to adjust air/fuel/ for the maximum efficiency. In my 3.2 I get about 30 mpg (UK)(24mpg (US)) when doing a (more or less) constant 65mph. Although a more powerful car, my 993 seems to get about the same in the same circumstances. "Walk on her" however and the fuel rapidly disappears. Cheers

My example of one is not statistically relevant. Nevertheless, sort of as an experiment I drove 628 km (390 miles) in light traffic from New Jersey to Quebec. Where possible, I drove at a steady state of 3000 rpm = 100 kph (+/- 62 mph) with the gearing that my car has (7:31).

I got 7.78 liters per 100 km (30.2 mpg U.S.). The car is a 1974 coupe, but has a '75, 2.7L S engine with C.I.S.

Edit: My engine is totally stock.

With MegaSquirt running 80lb injectors running AFR's in the low 15's and timing in the 40's, I saw 28MPG with mostly highway. There was some city mixed in.

My car is an 87 with 3.4L and only 7.5:1 compression ratio. If I had the normal CR or higher, eclipsing 30MPG's shouldn't be hard I'd imagine.

What I can add to this is last year my son and I went on a road trip. We both filled up on Long Island drove up to the Catskills stayed together all day drove the cars the same and at the end of the day he was under a 1/4 tank and I had about a half tank left. So my 3.2 gets better gas mileage than his 3.0. That's all I have FWIW. I thought the gas tanks were 21 gal not 16 ???

Gearing is a big overall factor. The mileage on modern cars with some of these slick 8-speed transmissions is amazing. I probably get the same MPG in the 3.2 flat 6 '84 carrera as I do in a '11 BMW M3 with a 4.0L V8 and a 6-speed on the highway.

Wow Jerome! Admitedly I'm probably not the most economical driver when in a 911....I let the car run away with me at times....LOL. Around here (PNW) at normal times, it's very difficult to maintain a constant speed that is even at the posted limit. The left lane is often clogged with vehicles doing 10-15 mph under the limit...even when traffic isn't heavy. In our cars, that often means 5th or 6th cannot be used, and when "blue sky" shows up, I'm accelerating before the opportunity is gone (killing econonomy). Is Quebec any better? I was born, raised and learned to drive in Quebec and at the time it was somewhere between Europe and the rest of North America as far as pace goes. Cheers

I just completed my first trip in my 84 3.2. Stock except for a S.W chip and a Dansk sport exhaust. After 830 miles going from sea level to 10,000' and back I averaged 26.7 mpg. I also drive between 80 and 90 mph on the hwy. I am pleased.

Do tell!! I'm so subscribed!

He simply runs a lot of timing plus AFR's higher than stoch.

Yes, that's correct. I mapped the part throttle fuel AFRs in the cruise and light load regions to run in the 15-16s which is leaner than 14.7:1, which is the stoichiometric mix the O2 sensor tries to adjust it to, disconnected the O2 sensor to disable it from readjusting the mixture, and added a bit more ignition advance in these leaner areas to compensate for the slower burn of a lean mixture.

I leave full throttle fuel and ignition tables mapped for max power, so when it's needed, just press full down on the gas pedal.

Mpg
 

We get 26mpg FWY on our stock '86.

interesting concept, I have been toying with this idea on my EFI930 build. I can even program in the target AFR to my tec3.

As soon as I get my cruise to run smoother. So far, my car likes to go into lean misfire when I get even close to 14.7 :confused: