I've been taking data, and I'm convinced engine temp might be the single biggest factor in determining my mileage in the city. Here are a sample of my numbers from today over various trips I've taken. The first number is my engine temp as indicated by my UG at the end of the trip. The second number is my mpg from the trip. The first trip was from a cold start; the rest were warm.
152/27.9
181/31.1
190/39.1
176/29.2
Other variables that surely impacted it included my trip distances, trip mph, intake temp, and so on. I recorded those too. Engine temp seems to have the highest loading so far, however. I've been experimenting with various forms of insulation here too. The most successful to this point have been cardboard blocks around the radiator. I'll be very interested in seeing how your numbers are affected by your mods here.
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