Driving around in my automobile, The 3.2 giving me about 32 mpg. Flipped HB Options

[worn]

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.

[technicalninja]

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...

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.

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.