[Ladogaboy]

I'm curious about the relationship between estimated increases in mileage. Most often, I hear the expected/anticipated increase in percentages, but I'm not sure what the relation is to actual.

For instance, if modification X is estimated to produce a 10% improvement in fuel economy, and X is performed on vehicles A (~ 20 mpg) and B (~ 30 mpg), would A see a 2 mpg improvement while B sees a 3 mpg improvement? Basically, do these modifications become more substantial as the vehicle's base mpg increase? tiy