[Cd]

I plan to eventually do some throttle stop testing on my car to estimate the cars' new cD, but for now, the geek in me would like to know if I can get a really rough guess at the change in cD based on changes in fuel consumption.

Here is a quote : To put Cd changes in perspective, Frasher put some numbers to a hypothetical sedan. Our imaginary car has a curb weight of 3,527 pounds, a Cd of 0.30, a frontal area of 23.7 square feet and 9 pounds of rolling resistance for every 1,000 pounds of weight.

According to Frasher, "If we put a gas-burning engine in this car, expect reasonable performance and drive it on a combined driving cycle, we can expect to get 23.8 mpg…. Add 10 percent to the drag coefficient, we'll now get 23.3 mpg…. Take 10 percent from the drag coefficient, we'll now get 24.3 mpg."

So I drive a 1993 Honda Civic hunchback.
The car has a approximate weight of '2,094' lbs. when new, with mine maybe being 100 lbs heavier with it's automatic transmission and aero mods I have added.

Dimensions: 160″ L x 67″ W x 51″ H for the frontal area

Rolling resistance ? ....no idea.

Stock, the factory quoted cD is .31

Highway MPG is 41 stock

So given these figures, what rough guess can we get at change in cD if there is an increase in MPG by

A ) 5 MPG
B ) 10 MPG