This data suggest that merely installing an overdrive
unit on an RX8 will improve the MPG to 35 on the highway.
The RX8 engine is turning 3000 RPM at 80 MPH.
A Corvette turns less than 2000 RPM at 80 MPH and gets 25 MPG.
Both cars need less than 40 HP to go 80 MPH.
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"It's been 2 decades since Detroit began offering overdrive
transmissions as original equipment in virtually all vehicles rolling
off their assembly lines. And while the OEM's intent was to improve fuel
economy
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and decrease engine wear, it wasn't long before enthusiasts realized the
performance gains that were possible by adding another gear with a ratio
of less than one-to-one. With overdrive in high gear hot rods could
benefit by using a lower (higher numerically) rearend gear, which
translated to greater acceleration without the inconvenience of higher
rpm while cruising at highway speeds. This was akin to having your cake
and eating it to, as high-output engines were allowed to run in their
power range while blasting from stop light to stop light, only to be
given a reprieve when it came time to hit the open road. "
Paul Lamar
I would disagree with this assertion. We have a friend living in
the apartment under our house, and he has an RX8. He claims an
improvement of 2 or more MPG keeping the rpms in the 3500 to 4000 range
instead of lugging it down in 6th gear. We live in the Florida Keys,
with the speed limit 45 for 20 to 40 miles at a stretch. For a long time
he was complaining about the mileage he gets around here. We talked
about the airplane engine version, and how its "happy place" was around
6k. I suggested he get his rpms up a bit and see what happened. For a
week he ran in 4th and 5th gear, and reported a gain from 14 to 16 mpg.
While my diesel is quite happy running at 1600 rpm at 65 mph getting
24.8 mpg, I think the rotary needs a bit more speed to breathe better.
Highway speeds might change it a bit, the next time he goes to
Miami maybe he can check it.
Kevin Alderman
My RX8 will happily run at 45 MPH in sixth gear at 2200 RPM.
It will pull away at zero MPH with out depressing the throttle pedal
in first gear from 650 RPM. It gets a steady 25 MPG at a cruise
control setting
of 65 MPH.
I would have to ride with this fellow. Some people have a bad habit
of pumping
the gas pedal to maintain a fixed speed.
It runs at stoichiometric 98% of the time.
You can calculate the fuel burn from this OBD II data on the RX8.
One pound of fuel per 14.7 pounds of air.
Paul Lamar
-- I am not sure how he drives- but he is a 20 year old that
routinely runs out of gas. That alone tells me that he isn't that great
at planning and/ or executing.
Do you think that your rx8 would get better mpg if you could OD it down
to around 1900 rpm?
KA
Yep.
Going 45 MPH in 4th gear gives a lower BMEP (torque).
Sixth gear will up the BMEP.
I think I can make an Overdrive out of a FORD Auto tranny front planet.
With gas at $4 a gallon it could pay off.
It should pop out of overdrive if the pedal was suddenly floored and the
intake
pressure increased.
Tell me about the speed limit in the keys. I got a speeding ticket for
going 55 mph at 3 am :)
Paul Lamar
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