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Wow, I took it on the freeway to get some cheap Costco gasoline today and the dash indicated 25.5mpg@65mph in cruise control! That's a huge improvement over 23.0mpg stock. I had tape over the oil cooler in a slight different position so it blocks a little more of it off, but the oil definitely could not have been much above 100C because the freeway was a very short distance away and I immediately turned on cruise control to check the mpg gauge.
I think my intake cam retard must be responsible for most of it. I believe the cam should be something like 10-12 degrees retarded from its stock position, which should be in the vicinity of 5% reduction in volumetric efficiency, while internal EGR according to my simplistic modeling (residual exhaust gas + overlap * constant / rpm) should be down something on the order of 2%, so pumping losses are probably unchanged (EGR heats up the air) while combustion efficiency is up for one reason or another. It could be due to the fact that ignition timing appears unaffected by VVT, and now I have a faster burning mixture with the same ignition timing.
This kind of exceeded my expectations. 26mpg is probably within reach if I add a little more tape to the grille, 27mpg may be within reach with some external EGR, and 28mpg could be possible with thinner oil, which is honestly pretty respectable...a lot of V6 cars can't do much better.
I also realized that I could get mildly warm air if I do airbox and intake snorkel deletes (planned for when the air filters need replacement) and then tape off the entire bottom of the grille, as the engine would suck warmed air through the front bottom of the radiator from inside the engine bay. It would only be barely warm but it probably counts for something on a long trip and only needs a few strips of tape.
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