One other thing to pay close attention to is the timing. At lower RPMs with even a modest load, timing can drop to almost zero which can seriously affect fuel economy. This is done in order to help prevent detonation under those types of load conditions. Larger tires compound the problem by dropping the RPM at certain speeds.
For example, my Expy with 3.31 gears gets better fuel economy at 80 than it does at 75 because of the load and RPM range. Oddly enough though, it also gets good economy at 65 which, despite the lower RPM and load range, I assume is due to the lower wind resistance at that speed.
One other thing to remember is that in order to help reduce droning from the CAI kits, we remove the modified Cam Timing curves and revert back to the stock ones. This has a slight economy hit as well.
Take care.
__________________
Bill Cohron - The Mad Doctor  
Power Hungry Performance - The ORIGINAL in Ford performance tuning... Since 1997!
(678) 890-1110
www.gopowerhungry.com - Home of the Hydra Chip, Minotaur Tuning Software, and the new Orion Reflash System for Navistar!
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