Originally Posted by joelg1988
I get about 34 mpg with very aggressive driving (A/C off). But since it's now May and temps here in Vegas are starting to hit 100 degrees, I get 32 mpg with aggressive driving (with A/C on) and 38 mpg slow driving with A/C on.
I guess it's only easy to get 40+ mpg with the A/C off. Once you turn on the A/C compressor, you lose 5 mpg (or more, depending on how you drive) easily.
My V8 Camaro only loses about 1 mpg with the compressor on. Looks like our little FrankenMazda is not happy with the compressor on.
No fault of the frankenMazda!
On a car like a V8 Camaro...
+ You have a higher amount of air to waste power moving through ( the car is significantly wider and less streamlined, but perhaps just as tall ).
+ You have a transmission that needs to transmit over 4 times the torque, so the drivetrain losses make up a significant amount of load to move the car. The lower the load of the drivetrain is ( IE when cruising at a steady speed on the highway ), the higher % this is of the horsepower needed to move the car along.
+ That rear differential also adds to this drivetrain friction.
+ Your engine has over 3 times the displacement, and at a low load such as highway cruising, it also takes a big friction and pumping loss penalty.
The Load that comes with a ~3 horsepower compressor turning on easily disappears in the noise of all these losses.
But on our very aerodynamically optimized ( this car is smaller than a Prius ) cars, an extra 3 horsepower load is a big kick in the balls.