I just discovered something disturbing about my fuel efficiency and need validation.

I have a 4AT RX-8 and have been getting about 17-19 MPG on average in a 25/75 mix of city/highway. I'm a conservative 65 mph driver (egads!).

However, the past weekend I made 2 high-speed runs on the highway (in warmer weather, no less) at 90 mph average, totalling about 170 miles. The fuel gauge was still almost 2/3 full!

Then, I ran those 2 routes again in the evening at my stately 65 mph. After the 1st leg, I was out of fuel (about 100 miles). Total out of the tank was 279 miles, which is a LOT more then I usually get.

My hypothesis is that this engine is geared for efficiency at higher than the 60 mph that most other piston engines are geared for. Any thoughts?

 

I average between 85-105 on highway, and my around town mileage of 12-13 doubles. I would say that makes this an efficient car at higher speeds

 

Gosh, I wish my automatic would get 17-18 mpg......should I drive faster!!!:] Yipee.

 

Could I use that as an excuse to the highway patrol?

"I'm trying to get more efficiency out of my car!"

Thanks all.

 

"If I don't speed I'm not gonna make it to the next gas station! For crying out loud officer, this is a rotary engine, don't you know anything?"

That oughta do it!

 

LMAO!

 

that's not an accurate measurement. Especially the "almost 2/3 full".

I can understand you're excited by the observation but I would not give much on estimates based on the fuel gauge.


I have to report that I got my best-ever mpg value on a roadtrip to Sacramento, with an *average* speed of 80 mph.

My daily driving is freeways as well, but *averaging* only 60.

 

As much as I would like to believe the 'tuned for best fuel efficiency at 85 mph' theory, it doesn't make sense.

Someone here explained that and why you get best fuel efficiency by driving in the highest gear possible at the lowest rpm possible.

I don't know how it is with the automatic transmission but the MT goes in 6th gear:
3000 rpm -> ~60 mph
2000 rpm -> ~40 mph

The optimal mpg could probably be observed driving 40 mph in 6th gear. The owner's manual lists those conservative shift points, I think they say get into 6th gear at speeds of 47 mph, :-)

That's the theory. Anyone on this board ever done this for more than a minute?

 

Actually leaving work yesterday I shifted at all of the recommended shift points..
After which I looked over at my wife and said "I'll bet you didn't know that this car could accelerate that slow!"
It damn near caused me physical pain to drive the car like that.

 

lmao