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1987-1991 Parley with regards to your 1987 to 1991 Bonneville, Olds 88 or Buick Le Sabre Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 04-09-2005, 10:19 PM   #31
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I feel like mine is still coasting at 75mph (ok, not quite coasting). But I don't have to press the gas down far at all, especially when I am alone, that is why it works so well on long trips. It really likes to cruise at that speed. Until I installed the strut tower brace, anything faster was not too stable when changing lanes. Now with good tires and the STB, I can do whatever traffic is doing and be just fine.

But to link this all back to the original thread... anything over 80 and MPG drops off dramatically for me, sustaining 85 will drop it down to around 20-22 mpg while 75 will get 30 mpg, big difference.
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Old 04-10-2005, 12:18 AM   #32
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dont you get the best gas mileage at the top of the torque curve <2k rpm>?
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Old 04-10-2005, 11:17 AM   #33
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Well, you'll get the BEST fuel economy at the lowest possible RPM. However, if you need to go up a hill, or something that requires more rpm, that means you will have to rev the engine up more.. which uses more fuel like that. Basically, having the engine at it'* peak torque [when your torque is low in the RPM range, of course], is best, because if you go up a hill, chances are the engine won't need extra RPM.

It'* a known fact that stale, low RPM yields higer fuel economy [IE NOT accelerating] a car gets better fuel economy at lower RPM. However just because the RPMs are low, doesn't mean you are getting the best fuel economy. Like if you are in 2nd gear.. you know that horrible gear we all dread? Well, if you have your foot to the floor, and you are at 2500 RPM, you aren't getting good fuel economy.


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Old 04-10-2005, 12:29 PM   #34
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I would agree that the best mpg is at lowest rpm in top gear WITHOUT wind resistance. Wind resistance is just like a hill for our cars. Going 55 at 1500 rpm without a car infront of you still requires the car to overcome that wind. Since it is not producing as much power at that speed, it has to compensate with more fuel. Around 1750-2000 rpm wind AND hills do not require quite as much compensation to overcome. The only time I got 30 mpg doing 60-65 was when I followed a semi for 250 miles, no wind resistance. Other than that, 70-75 has always been the speed to go. In my girlfriends Series II 3800, the best speed is right at 65-70 since it is geared a little differently and it runs 2000 rpm in that range. Her mpg starts to drop off over 70 usually.
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