From what I'm reading the speedo is inaccurate, about 8% off, but I'm reading that the ODOMETER is actually pretty accurate with stock tires sizes, and that using a larger front tire to correct the speedo puts the odo off. I just got 48 and 54 mpg on an 86 with high mileage, ear shaved, coastered, jetted #40/#138.
"Fiamma" - 86½ Pontiac Fiero GT fastback
Frame-off resto w/ Cobalt SS F23 trans swap, high lift valves, sprint headers, de-cat etc.
Track ready adjustable suspension w/ poly bushings & Herb Adams antisway bars
Too much other stuff to list. 100% built with my own two hands.
94/86 VN750s - Ears shaved, coastered, jetted, R/R moved.