With gasoline prices being what they are, I wonder if anyone has tinkered with various speeds to see at what speeds would one get the best fuel economy (everything else being equal). I have a 1997 Bonneville with a 3800 Series II from an " '01 or '02 Buick LeSabre" and I assume the transmission is obvious & ubiquitous (that there are a million identical or nearly-identical engine / transmission combo'* out there).
Is this a simple matter of lower RPM'* are better? I know it gets better gas mileage at 55 mph or 90 KM/h than at 62 or 63 mph (100 KM/h is 62.5 mph) but I am not going to do 85 KM/H for 2 hours just to try it out: I'm hoping someone else has!

Related, I hope: I have found best gas mileage after several (4-5) consecutive tanks of 92 Octane gasohol, and if you want to point out that makes no sense, save your breath / keystrokes, I already know that. But it works. 94 Octane gasohol with octane boost and it goes down to about the same as 90 Octane gasohol. By gasohol I mean (E= <10%) or that it'* ethanol blend, not more than 10% ethanol. FWIW the octane boost was NOS with a touch of nitromethane in it. I also constantly use what *I* call "MoleKule mix" also called "the brew" or MBF (MolaKule Brew Fuel???) A FINE gent (MoleKule) on another board (abbreviated "BITOG") is a chemist or something with secrecy agreements with a few companies. I believe he is legally OK, however, JUST saying trust me, the best daily-driver mix is 1 part Schaeffer'* Neutra to 3 parts FP (Fuel Power) and add 1 oz. per five gallons. And ask him nothing of how or why.
What'* the state of those instant fuel-consumption meters? I'm thinking something more than a vacuum guage; I heard about that one 20 years ago.
Is there a point to cranking up nominal timing? Having a "summer thermostat"

I want to drive to beaches LOTS in the next 2-3 months and I know going over 100 KM/h really guzzles.
Thankyou very much in advance
Rob in Winnipeg

120kmh I get the best economy that should be 75mph. I get about 29mpg with the ssei and 31mpg with the olds.

at 130kmh or or 80mph i get about 28 with the ssei.

have you replaced your o2 sensor and cat?

oh i also should add the olds has the grany gear trans of 2.84 so it will get 30 at several highway speeds.

I just finshed a 800 mile round trip through the NC mountains, with a full load of people on board. I averaged around 27 MPG, and I generally ran around 70 MPH. If I had ran around 60 MPH, I am sure I could have hit 30 MPG. I would say the best "trade-off" (speed vs. MPG) speed would be 65 MPH for me.

NCC

I've pulled 31 with my 93, and 30 with the 95. It'* quite possible to get that in any car on the Forum.

Buick_Engine, can you put your year and trim level in your signature?

At an avg. speed (cruise control doesn't work) of 110kmh (70mph) with highway and (35mph) city driving I get around 26-27mpg.

Last weekend on a 300 mile highway trip home at an avg. speed of 100kmh (60mph) @ 1900-2000rpms I got 33mpg - 480km on exactly half a tank.

. The highest mpg I've seen is 21 on a 300+ mile trip. And No Will , I wasnt Nitrousing to the Hershey Show. I average 14 and it has gone as low as 10.8. you must have meant just 3800'* right?

I would get 23-24 at 74. I slowed down recently to 68 for gas prices, and I get a little over 26.

13 mpg city, haha, highest i've gotten was 16mpg.