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General tuning question - fuel economy



Not having really any engine "tuning" experience I stumble on some of the
basic concepts (such as when to add spark advance).  My rebuilt 350 TPI
F-body gets about 20% less highway gas mileage with its bigger cam (GM ZZ3)
and stock computer.  I figure more air in at X rpm requires more fuel to
appease the O2 sensor, hence gas mileage goes down.  How do I compensate, or
can I?  I noticed there are some Hiway mode parameters, such as Hiway spark
add (?), in the 165 ECM that I could take advantage of.  Or, is the only way
to get better mileage mean changing the target AFR?

However, I also thought that this engine cruises at about 2200 rpm on the
highway at 75 mph.  I'm wondering if the different cam (and valve timing)
has defeated the ram tuning effect of the runners and made the engine less
efficient on the highway.  Any thoughts?  I'd appreciate a little basic
help.  Since this car is my daily driver (70+ per day) I'd like to keep fuel
economy in mind when tuning.

Thanks,
Steve Marteney
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