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Old 01-29-2008, 06:40 AM
livvie livvie is offline
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Default Re: 87 vs 91 octane for better mpg?

Quote:
Originally Posted by Tim K View Post
The bottom line is pretty simple....

Use what the manufacturer recommends. They are telling you what the engine was designed to run on. Using anything else will likely have a negative effect on both your performance and fuel economy.

(I'm sure someone somewhere will post that in THEIR car THEY got better performance using a different fuel rating than recommended. In reality, your car will run best on what is recommended unless there is a problem with your vehicle...in which case the right action is to get it fixed not change fuel rating.)
This is all assuming the manufacturers are giving you a number from the engineering group. Marketing can always have a say in the number if they feel it is in the best interest of the company to market the car at a lower octane level. The engineering group will sign off saying it can be tuned to the lower octane level but actually can perform better at the higher octane level. I believe the Prius engine (atkinson cycle engine) is such a case.

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