Ok, the tank I just posted is my highest, to date. From what I've been able to experience, a grill block helps.
I tried a grill block by just blocking off the inlets with packaging tape, which looks pretty ugly and it did have some positive effects. I changed to a cardboard shaped grill block, with more of a lower nose to it.
With this change, I have had my highest mileage tank, so far. This tank was a combination of about 2/3 freeway and 1/3 city, although a good portion of the freeway driving was stop and go traffic.
Highly recommend this modification. It appears to be capable of delivering 5%-10%, in my experience.
I'm having trouble separating whether the improvement is from getting and keeping the engine warmed up sooner
aerodynamic improvements from less turbulence in the engine compartment and under the car.
You folks think it's both? Or?
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.
From my experience I believe it's totally due to the aerodynamic impact. I have mine blocked off so that it's down to a couple of 3"*4" holes, one in each side. The engine temperature in that configuration runs the same as it did before I did the block. I did run a little warmer going up hills, so that's why I made the second opening. As it warms up I anticipate putting either more openings or removing the grill block, to keep the temperature at it's normal range.
I have been fiddling with my grill block in the last week or two. I am trying to get a balance between keeping the engine coolant at 190+ degrees F while NOT overheating when I am stuck in traffic. I don't like going above 210 degrees F, so I have a narrow window to work with. This temperature window is my "comfort zone". Maybe I could go higher, but I don't want to until and/or unless I learn more about the engine's safety zone.
One thing that I have found is that with a full grill block, my "mixed air" warm air intake doesn't provide enough hot air. I figured out that with the grill block, the air around the exhaust header (front and center in my engine bay like most front wheel drive cars) is stagnant and does not move into the airbox. With a grill block that is partly opened (bottom dead center), the outside air being pushed into the engine bay allows the hot air to get pushed into the airbox.
Alternatively, I could restore my air dam to push that air in and go with a full grill block and see what happens.
This may be something that only I am seeing because of my "mixed air" hot air intake. Other people probably won't see this if they go with 100% hot air from the exhaust header or use the IAT resistor mod.