Let's first all agree with the following statements:
- No two engines are alike; tolerances, configurations, and state of tune.
- Variable timing, and distributor wear, coils, etc and advance differences.
- Fuel configurations, AFM settings, fuel maps, etc.
With that out of the way, let's not talk what we know and our experience, but let's show what we have observed, and lets support it with some data...
I'm fortunate enough to have digital logging capabilities, and somewhat accurate temperature probes on the air intake and head-surface of the #3 cylinder.
For this experiment I "pre-heated" my engine, and went for a 60 minute ride. I purposley emposed "13.0:1" across my entire fuel map, including steady idle at "13.0:1".
Here are somewhat relevant tid-bits:
- Idle: 900RPM at close to 11 BTDC . Max mechanical advance: 28 BTDC @ 3000 RPM.
- Fuel: 2 squirts per two crank revolutions; or 1 engine cycle. (same or similar pulse as stock L-Jetronic as if you tuned your idle for 13.0:1 AFR)
- Engine: stock cam, 42mm intake x 36mm exhaust valves.
- Stock Fan.
- Stock Heater Boxes.
- Working thermostat.
- Conditions: 70F ambient, city driving, some hills.
Here is somewhat raw data....
CLT - #3 cylinder head surface temperature - TempII Sensor location - in Fahrenheit (F).
MAT - Manifold air temperature (Intake AIR Temperature) - in Fahrenheit (F).
RPM - Revolutions Per Minute
AFR - AIR to FUEL RATIO
Hits - The number of times that event was observed
Let's break that down a bit...
First filter, 800-1000 RPM; Second filter, 1000-2000 RPM; Third filter, 2000-3000RPM;
Fourth Filter, 3000-4000 RPM, Fifth Filter, 4000-5000RPM.
