That's crap, I have a B16B Civic Type R swap in my 2000 Civic Si, the CTR transmission has lower gear ratios than the stock B16A transmission so my car is at a steady 4,000RPM at 70MPH and I still manage to get 32MPG mixed driving. I've gotten over 350 miles per tank with the car's 12.5 gallon fuel tank.

 

a few years ago on in a stick 2000 civic ex(D16Y8) I was getting around 33mpg with about 70% HWY driving.

with a turbo I'm getting 30mpg in the same conditions. And obviously it sees boost every day.

 

I get 28-33mpg depending on how I drive. The best I ever got was 37.5 on the highway and driving like a grandma.

 

The owners manual says you can use 87 octane but you'll notice a decrease in performance and mileage. It can actually run on both. Premium fuel is a no brainer though.

 

I know the gas cap says to use premium fuel only, but I almost always fill up with standard 87 unleaded. My average miles to a tank with all highway miles, which has been tested quite a few times, is about 300-320 to a tank. With a good mix of highway and city driving, I almost always get 270 miles...

 

as does my Si as 70 mph