I find that mileage can vary tremendously depending on how I drive. On a 200 mile highway cruise for example, I find I get about 35-37 mpg, while in aggressive city driving with frequent trips to redline, I'll get 23-25 mpg. The engine is a D16Y8 with JRSC and header.
Also, to get accurate mileage numbers, divide total miles/kilometers accumulated since last fill up by the total number of gallons/liters required to fill up the tank (don't "top off").