What's the most fuel-efficient speed for a IIA?

[Alaskan RoverIIA]

I always sort of keep track of what any particular vehicles "sweet-spot" is for road travel. By sweet-spot, I mean the speed at which the vehicle seems happiest. Now this doesn't necesarily mean the speed at which it gets its best MPG. The rover's "sweet-spot" seems to be around 35 mph. It just seems happiest at that speed.

But what I am wondering is: Has anybody figured out what is the most fuel-efficient road-speed for a IIA that doesn't have overdrive?

I recognize the fact that too LOW of a speed is just as bad for MPG as too high of a speed...as the engine is still ticking over at a certain rpm, consuming fuel, but traveling less distance per unit time.

The defining factor, then is at what point does coefficient of air friction become less of a detriment than fuel used per unit time if air friction were not a consideration.

I'm think the most fuel-efficient speed for an old rover might be anywhere from 35 to 45. I think anything over 45 or so, air-friction starts taking a big chunk out of MPG.

Anybody figure out any quantitative fuel-efficiency speeds?

[BGGB]

with my rover i've found the most fuel effiecent speed to be 0.

[crankin]

with my rover i've found the most fuel effiecent speed to be 0.
+1

Also, pushing it around in neutral seems to help my gas mileage...but than again I am in a series III.

Oh...also because of the bouncing speedo...my sweet spot is right around 20 to 55.

[LR Max]

with my rover i've found the most fuel effiecent speed to be 0.

My 109 is the most efficient when I park it and drive my little car. I didn't buy the 109 because its cheap and reliable. That is what my chebby is for :thumb-up:.

62 mph seems to be the magic number for rovers with 4 cylinders.

[yorker]

I think 45-50 is about ideal for MPG without an OD. If you had a BSFC chart for the 2.25 you could peg it down exactly.

[yorker]

1973 Motor road test:




Touring 17.8 MP IMPERIAL gallon
Overall 16.3

From graph - Steady Speed:

30 MPH - 25.5
40 MPH - 22
50 MPH - 18
60 MPH - 14

Max speed (banked circuit) 66.7 MPH
Best 1/4 mile 70.0 MPH
Terminal speed at 1/4 mile 57 MPH
mile 66 MPH
Speed in gears @ 5000 rpm - 1st - 21
2nd - 34
3rd - 54

Acceleration - 0 - 50 15.6
- 60 27.4

It was a Series 3 canvas hood SWB model DXC 959 L on 600 x 16 Dunlop Crossply tyres.

The standing 1/4 mile was 22.4 sec. The test was 1014 miles long and the speedo was dead accurate!

The brakes recorded a max stop of 0.89g at 95 lb pedal pressure.

The testers commented that:

'Despite this low gearing the acceleration is poor with 60 coming up in over 27 seconds, using the fur high-range ratios only, of course. the maximum speed will not worry the authorities either, the best flying quartermile was exactly 70 MPH, with a mean of 66.7mph at 4400 rpm - 400rpm past the peak power. Since the frontal area, weight (27.3cwt) and power are about the same as those of a pre-war luxury saloon, we feel that it ought to be able to pull a much higher top, unless Rover's engine output claims are exaggerated.'

[mongoswede]

haha...I read the heading to this thread and the first three posts were exactly what I was thinking :D

[stonefox]

Hey I didn't sign on for all these quantum physics questions here .This forum is really taxing my third grade edgamacation.
I'm going to have sit down and really drink this threw.:gulp:
All I know is my machine gets its best mpgs towed behind a tow truck.:eek:

[Alaskan RoverIIA]

I think 45-50 is about ideal for MPG without an OD. If you had a BSFC chart for the 2.25 you could peg it down exactly.

Yeah, that's about what I was thinking...actually, I put it closer to 40-45 mph. I've found that over 45 and the rover seems not to like it as well, and nothing is worse than driving a rover that is pissed-off at you. :)

Incidently, when my Rochester 1bbl was properly tuned and timing spot on. I would REGULARLY get 18-20 mpg, with an all-time high of 24mpg.
Mind you this was WITHOUT overdrive and without a backing wind.

For the person saying zero miles per hour is of course the best fuel mileage...as that would equate to ZERO miles per gallon, this would be the WORST fuel mileage, not the best.

To the person who posted the fuel and performance stats from 1973...THANKS! That was pretty interesting. My OWN, numbers are the following in terms of acceleration:

Zero to 60 miles per hour = 23 years. Meaning that during the past 23 years, I've only had it up to 60mph ONCE....and that was driving downhill in front of an heavily loaded logging truck in Alaska that was taking up ALL of my rear-view mirror! I think I hit 73 miles per hour that day, and immediately blew one of my exhaust valves.

Smiles per mile: infinite.

swear words per mile: WAY less than infinite!


BTW: My rover gets in the true "Chitty-Chitty Bang Bang" sweets-spot mode right at 35 mph. I just re-confirmed that today, driving down a wonderful back-country road in Ware Neck, Virginia. I was waiting for the wings to unfold, but they never did...I guess I have to work on that! :)

[SalemRover]

BTW: My rover gets in the true "Chitty-Chitty Bang Bang" sweets-spot mode right at 35 mph. I just re-confirmed that today, driving down a wonderful back-country road in Ware Neck, Virginia. I was waiting for the wings to unfold, but they never did...I guess I have to work on that! :)

I saw a movie of someone driving a back-country road in a series rover singing that song once. Was that you? :sly:

[RoverForm]

1973 Motor road test:
I found this extremely helpful.

[bkreutz]

1973 Motor road test:

I noticed in this article the mileage figures are for "imperial" gallons, since that's bigger than "our" gallons the mileage would be less. (I forget the formula for figuring how much larger the imperial gallon is)

[yorker]

http://www.markporthouse.net/rangie/fuelconsumptionconversion.htm

[Jim-ME]

IIRC an engine is most efficient between 80% of the rpms where max horsepower is obtained and the rpms where max torque is obtained. My 2.5 diesel is happiest running between 2000 and 3100 rpms. I seldom drive by the speedometer and always reply on my tach.
Jim