I been driving my 914 this summer. Closing in on 5 Kim so far this year. When I go, I get the highest octane that I can find; 91 or 92 with no EtOH where I live, trending towards more ethanol as we get west. So, I have been old guy writing down the numbers and have consistently hit 31 -32 mpg. This decreases if I leave my gas cap off just before a drive with the RRC 2024 folks.
The interstates let you drive at around 80 mph, and that adds up to a light throttle 3,000 rpm with my gears. The car must be pretty good with airflow.

Light weight really helps.

If you're hitting those numbers via gallons/miles calculations and that is the AVERAGE you're kicking ass on the economy numbers.

I believe you are beating the 4-cylinder factory numbers by 20% with nearly three times the power...

That's high enough mileage that I would want to see the AFR numbers.

I'd be worried about being too lean.

Still really good mileage numbers!

Isn’t that a Chuck Berry tune

The way life should be

I am a very law abiding driver in general, and the fifty five limit saved both gallons and lives. With all of that said, I saw almost no speeding on the interstates with the high speed limits. Maybe with so many miles to cover in this amazing country sometimes people just watch things go by and wait out the distances. As for that, I am grateful for my 914 to ride in.

I get around 32 with a stock djet. But at 4k on the highway… close to 90 with 16 inch wheels


And keep a paper log book of gas stops like a normal person should….

My 2056 gets about 20 in town, maybe 27 on a really good day on the highway. Anything over 60 starts to pull at that number. I have come to grips with that. It's still better than the 12 mpg I get with the mustang in town and 14 mpg I get with the explorer in town. Highway on those is 22 and 24 respectively.

Do I drive like grandma? Hell no. If you aren't playing in the 3k to 6k rpm range why are you driving a 914? If my mustang had a manual I can't even imagine how bad my mpg would be in that car.

Oh, and I used to get far better mileage before the cht and afr gauge. I like my heads, I don't want to buy new ones.

Truth be told I can't even get good mpg in the mini. I just can't drive that way. The volt, another story entirely.

I envy you. I have a 74 914 with an '87 Carrera 3.2L engine with Motronic FI and 916 Transaxle with Guard LSD. And I'm only averaging 22 MPG over the last 4000 miles including lots of time on Interstates. This was not unusual for the Carrera it came out of but I should be doing better.

Not if you are having fun....

My 2056 gets around 24-25 mph at 3400-3500 rpm. AFR is around 13.2-13.4. Check your plugs to make sure you are not running lean.

My 2056 gets close to 35 mpg cruising at 75 - 80 mph. Twin Webers

Flat terrain and a constant throttle opening help

Your AFR numbers are different than mine.

Air/Fuel ratio is usually based on air by weight/fuel by weight and stoic is 14.7/1

Often folks leave off the one.

14.7 is "perfect" combustion with exactly the right amount of oxygen to fuel for complete combustion of the fuel with "hopefully" the least amount of CO and HC being produced.

12.5 is rich, normally a max power mixture.

10.0 is PIG rich

16 is getting lean, some cars will do OK running 16. This is the beginning of "lean burn" IMO. You only want to see as high as 16 in cruise at speed.

18 is dangerously lean. A few max effort fuel economy vehicles run this high.
You need computer controlled hyper fast FI with multiple knock sensors to make this work.
Run an old school T4 with carbs at these numbers and you will MELT stuff...


What does 32-34 refer too?

The mileage numbers that members have been posting are interesting.
Even seriously modified cars can achieve decent numbers if driven in a "highly responsible" manner.

And that is NOT how I'd drive those cars.

I try to keep my cruise AFR between 13 and 14, but closer to 13. I think my air dam and such doesn't do any favors for mileage. That 6 might be hardly working moving a 914, however I would still want to know my head temps and AFR, and my engine won't cost 20k to rebuild.

HB gears in the 901 in the Alien. /i don't track mileage but it has to be good since I was able to tune the CIS.

Worn, I just did the Waumandee Hill climb/time trial last weekend. 2.3 miles with 400 ft elevation. Very fast, want to go next year. Mark

On the subject of AFR and mileage - I remember watching a video on YT, where the driver of an old school 911 (while basically being interviewed by the channel's host), running thru the twisties of some northern California mountain roads - would manually change the A/F ratio on the fly via a knob he had installed between the seats!!

I think he may have been running carbs but can't exactly remember. I thought that was kind of a slick solution and may try to mimic it at some point. Anyone heard of this before? Know how that could be done?

I set that up on my car. Very easy with d-jet. All you need to do is modify the resistance detected at the cht. I used a Bluetooth switch. Didn't keep it because it didn't affect head temps as much as I was hoping.

Can’t change AFR on the fly with carbs
As it would require a jet change on the carbs


Easy with djet
Possible with modern injection

@worn

Can you provide a little more info?
What tire size?
Stock 3.2 w/motronic?
What ratios on the 901? (A-F-?-?-HB)?
Were these numbers obtained at 80mph (1st post) or 55mph (second post)?
What RPM is the engine at 55mph with that HB?

Thanks for sharing!

well…YES. Sorry to lose contact. I dropped out when pca became organized.

14.7 is "stoichiometric" (with ethanol free anyways) "perfect" combustion, but that also means maximum possible head and exhaust temps

"Lean" is a relative term and isn't necessarily a bad thing. "lean of stoich" "Lean of peak power", "lean of peak EGT" are all different things. People need to be more specific when using the term "Lean" as vagueness leads to unnecessary fears and potentially people implementing poor tunes.

"Lean" isnt the enemy, more specifically with an air cooled motor its more running in the roughly 13.5-15.5 range, especially under load that is more likely to cook your heads

16+ is no problem at cruise (and cooler than 14.7) as long as you have the means to control the timing to burn it properly. Flame propagation speed slows down the further you get from 12.5:1 so without the ability to add the necessary timing then you are still combusting the gas when the exhaust valve opens and you get engine bucking and popping out the exhaust, so tricky with d-jet and carbs but enter modern EFI and wideband O2 monitoring and you can do some fun stuff!

Now that my Megasquirt equipped autocross car is a little more street friendly I have been experimenting in this area to see what is possible as far as head temps, fuel economy, and drivability. My entire 1000+ mile trip to Colorado and back for RRC a couple weeks ago 65% of my fuel map was 16:1 or leaner. Was targeting 16.2:1 but hadnt spent much time on the new tune so wasnt dialed in and was cruising some areas at 17 and 18+, no issues.

I’d guess I do about the same. 3.2 with stock DME injection. I use a tank or two each driving season and drive every weekend…

I posted this a while ago:

http://www.914world.com/bbs2/index.php?showtopic=364979

Given my 2.7 CIS and normal driving, my average is usually around 27-28mpg. I think that's pretty sweet considering my Wife's new Bronco averages 25-26mpg.

I think having an engine that doesn't have to work hard to push a car around helps.

13.2-13.4 AFR. Click to view attachment

My 71 2.7 twin plug with webers might see 14 mpg if I’m lucky.

At least it beats the 74 911 with an RS2.7 MFI, which I’ve yet to crack 13mpg. It’s prior 2.7 CIS moto saw 25 mpg.

All on ethanol free fuel.

When I road tripped the 3.2 conversion I saw 23mpg.

How in the hell are you seeing 30s?

He has gearing on his side

Thanks @JamesM

Made me do a bit of research. Found this which explains it a little deeper (and I like his videos)

https://www.youtube.com/watch?v=vcgmEKhCFTs

So, running lean does not specifically increase temps.

@Geezer914 If I was running carbs and non-computer-controlled timing the numbers you're hitting are EXACTLY what I'd be hunting (average).
Your plugs show this nicely.

Now, computer-controlled fuel and spark with proper data gathering I would be hunting in the 16+ range at cruise.
The "data" I'd want the system to make changes on is as follows.
Crank/cam degrees/position.
MAP/MAF.
Baro.
Throttle position, rate of advance.
AFR wideband
Cylinder head temps (all during provisioning, highest one in daily use)
Knock sensors. I'd want one for each bank.
EGT. useful during provisioning. CHT sensor may be enough for daily use.

Now, I believe running lean gives less room for error.
You have to be on top of everything to achieve reliability and longevity.
Once you update to modern equipment lots of improvements are possible.

To those folks who are getting crappy mileage my questions would be.
Are you running a wideband?
Are you logging the results?
And if so, what's your average cruise AFR?

I'd bet most of them are too rich.

Here is some really well presented data you might find helpful.

https://www.kitplanes.com/adding-direct-air...tio-monitoring/


Id suspect you are correct in that most if not all are running rich. Almost every car I have retuned for people has been rich, many VERY rich.

Rich is just the easy answer, far easier to get things to run without to many noticeable issues just by dumping a bunch of fuel in. Without vacuum advance you can usually be anywhere pretty much from 14.7 to 9.5:1 on the rich side of stoich and have an engine that runs without bucking or popping. On the lean side of 14.7 you can get to maybe 15.5 but you are already loosing power pretty quickly, so yeah, quick tuning by ear or feel its almost always going rich.


When you get near 16:1 you need to add advance to get a complete burn in time, but throw in the necessary advance and it cruises along just fine at 16 and leaner.

I don't generally talk about lean tuning because so many people don't have a good understanding of what they are doing and are more likely to create problems and/or damage something if they attempt it without a solid understanding of EFI, because as I said, rich is easy. Easier to explain to someone they can just setup their entire tune in the 12.1-13.5 range and everything just works VS explaining where in their map they can go lean, how lean they need to be, and how to setup the transitions from lean to rich in their fuel and timing maps to have a smooth experience and no hot spots etc.


Click to view attachment

Having trouble typing here after DePuytren’s correction so bear with me. It never ceases to amaze me how advances in technology have gone more into increasing weight and performance than towards fuel savings. The 914 is such a sweet car from that respect. Pushing relatively little with that wonderful 3.2 is so smooth, given that the engine's has quite a lot of torque considering that it comes out of a high performance car. I have the stock engine management, good oil temps and I can generally avoid using the brakes even in town on our belt line. This gives me some hope for the heads. Maybe I will check the plugs when I visit the car next month. Hello, did you miss me?

I think that would be driving along in my calabaloose but I could maybe need a spelling lesson.

Oh, but that looks like fun to drive.

That second link (kit planes) is EXCELLENT!!!
It gets pretty deep quickly but was damn interesting to read.
I've always wondered about widebands and 100LL!
One of the vehicles I service is the fuel truck for the Pecan Plantation airfield.
I can have 100LL delivered!

NTK sensors are the way to go.
The Japanese kick ass again!

@JamesM thank you for the link.
With what you know don't you absolutely hate it when you cannot adjust fuel/timing at will, with the stroke of a few keys?
Having to resort to mechanical advance with vacuum operated advance/retard just seems "Retarded" in my book.
It's a wonder it worked as well as it did!

Yup! And the reliability of the mostly stock 3.2 Carrera motor gives me the confidence to take it anywhere.

I would say I absolutely prefer to be able to adjust fuel and timing with the stroke of a few keys but don't mind the old way either (though not a huge fan of carbs). If anything working with fully programable EFI has been incredibly educational in understanding the relationship between fuel, air, and timing and helped greatly when diagnosing and tuning non-programable systems, after all 3 of my 914s are still running D-jet. My favorite part about modern programable EFI is that you can setup a tune in ways that just is not possible with mechanical distributors and older injection or carbs as well as the precision you can gain from using 3 dimensional maps vs analog curves. You are not going to get a d-jet car running smoothly and safely at 16+:1 at cruise while still hitting 12.5:1 under load and maintaining a perfect idle, just as a limitation of the technology.

I am poking at this at the moment (quest for cooler heads and better mileage). I thinned out my mixture a hair (quarterish turn tighter on the inner screw). I didn't hit the interstate yesterday on my way to the autocross event, but I did get a good long 50 mile stretch of 60 heading up Seneca lake. With a little throttle, just barely open but 'open' it sits at 14.5-15 now, it was around 13.5-14 before (12-15inhg). Vacuum advance hooked up (123 dizzy). However, on the flats or slight decline where I am really just barely opening the throttle it dips to 12afr (16-21inhg). I kind of ignore that since it just can't get any air at that point and I don't think the MPS can do anything at the high vacuums my engine pulls (can't really resolve much down there).

On a slight climb it drops to 13 (11-9inhg) and anything under 7inhg or so it dips to 12. WOT it stays between 12-12.5 depending on conditions, it will go below 12 due to the TPS enrichenment.

Driving around town at 30 in 3rd gear I end up with the same super rich scenario as cruising at 60 with a pretty much almost closed throttle. Cruising 30 on a flat in 3rd is around 19-20inhg. Idle hot is 22.5inhg and 12:1 on the gauge. I have my ECU about 4 clicks lean from factory.

I think if I try to thin it any more at cruise, I will have to compensate by altering the outer screw and possibly the stop, not fun. Might be able to get away with just the stop to richen the WOT but the transition feels good now, so I hate to touch the outer screw.


CHT's were good but it was 45 degrees on the way there. 70 on the way home and it didn't go over 374 climbing hills in 5th.
Oil temp barely hit 180, but it was a cool day.