> I did that for 80 MPH because I know the RX8 engine runs
> at 4000 RPM in sixth gear at 80 MPH. I calculated the
> fuel burn given the .67 BSFC at about 30 pounds of fuel
> per hour. That is about 5 gallons an hour or about 16
> MPG. Not far off what an RX8 will really do at a steady 80 MPH.
> My measurements using the real time OBD II data indicates
> the RX8 will get roughly 20 MPG at a steady 80 MPH.
> You can calculate the pounds of fuel burned by dividing
> the OBD II mass air flow data by 14.7. 14.7 is represented
> as one in the OBD II charts. I have included some for
> reference.
>
> If you changed the RX8 rear axle ratio for 3000 RPM at 80 MPH
> the BSFC would drop to 0.57. Fuel burn would drop to
> 15.6 pounds per hour or 4.3 gallons per hour and MPG
> would jump to 18.6. That is about a 16% improvement
> in steady speed MPG.
> Paul Lamar
------------------------------------------
Paul,
My "91" RX-7 gets 24-26 mpg, @ 3000 rpm, which for my car is 80 MPH.
This is actual driving in the high desert of central OR. 3500' Elv. I go
into the valley all the time, going over the Cascades to get there. I
usually cruse @ 80- 90, sometimes pushing to 100 to get around trucks. I
have never seen mpg below 21.5 mpg, that is mostly when I do just city
driving.
I don't know what the rear axle ratio is. This car has 140,000 miles on
it,
and these mpg's are all with the top down! (;.)
I keep telling myself, some day, I'll drive at a steady 60-65 mph, just to
see what mpg I get. And then I start driving again.
Tom Phy
-------------------------------------------------
I had no idea the 3rd gen RX7 was/is geared that high.
Of course it is a turbo so it generates more torque at 3000 RPM.
I wonder why Mazda geared the RX8 at 4000 RPM at 80 MPH?
As I said the BSFC chart I was working with is 50 years old.
A friend just drove his RX8 to Las Vegas and back to LA
claiming to hit 103 MPH and averaged 21.4 MPG.
Thanks for the new data.
--
Paul Lamar ...No rotor no motor.
When I am at 80 mph, and need to pass right now, for more torque, I drop to
3rd gear and take it to 7500 rpm or more. At that rpm, my car doesn't seem
to have much more umph left.
TP
You need to P-port it Tom :)
Paul Lamar
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