Cruising AFR
If I can get it to be consistent, open loop 15.2:1 in most cruise areas. However, I have interlaced the fuel map so some cruise spots are 14.8:1 and some are 15:1, that way the engine does not always sit at 15.2:1 for extended periods. There is not much fuel to be saved by running it slightly leaner, some for sure but not much.
The real economy is in the timing. Pull out timing until EGT goes up noticably to establish a lower limit, then gradually add timing until your datalogs are showing a severe diminishing returns (less and less EGT drop for additional timing added). Many different engines I have tuned, all seem to fall in the 33*-40* range for optimal cruise timing. For the most part. Ancient chevys like 1985 year 2-piece block iron heads low compression, emission heads with carbs on 93 would take 44* (and 36 total WOT) but newer engines need much less.
The real economy is in the timing. Pull out timing until EGT goes up noticably to establish a lower limit, then gradually add timing until your datalogs are showing a severe diminishing returns (less and less EGT drop for additional timing added). Many different engines I have tuned, all seem to fall in the 33*-40* range for optimal cruise timing. For the most part. Ancient chevys like 1985 year 2-piece block iron heads low compression, emission heads with carbs on 93 would take 44* (and 36 total WOT) but newer engines need much less.
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Verdad Gallardo As much vacuum as you can squeeze. Adding the correct timing (do not add too much!) and watching EGT drop should give you some additional vacuum signal and a lower throttle position as the engine makes better use of it's fuel. You can also reduce vehicle weight, adjust tire pressure, alignment, lower brake drag, grease fittings/replace bearings, better balance rotating parts, make the vehicle more aerodynamic for higher speeds, use less friction tire compound, all of this should make the vehicle more fuel efficient and increase engine vacuum during cruise given the same displacement engine.
In the old days before widebands and fancy EFI engines, we would read plugs and adjust fuel/timing for better engine vacuum cruise.
In the old days before widebands and fancy EFI engines, we would read plugs and adjust fuel/timing for better engine vacuum cruise.
