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Is there any difference in MPG when you use 91 vs 87 gas?

5499 Views 9 Replies 7 Participants Last post by  ceric
Is there any difference in MPG when you use 91 vs 87 gas?

I'm currently only using the 87 octane at the gas station for obvious reasons. The gas price is here in the SF Bay area around $2.51 although I got gas last week for $2.41 at Costo. I get roughly 52 MPG with freeway miles. Not bad.

Has anyone checked out to see if there's a difference between the 87 and 91 octane or perhaps the 89.

Thanks for replying. Happy Prius driving :D
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Is knocking harmful?
Occasional light knocking won't harm your engines, and doesn't indicate a need for higher octane. But don't ignore severe knocking. A heavy or persistent knock can lead to engine damage.

IMHO, the knocking does not harm today's engines (due to better design than old ones), however, unthoroughly burnt exhaust would harm your CAT(cat. converter) and gradually shorten its life.

Come to think of it, most cars either recommend 87 or 91, who is buying 89 octane anyway?!

In some other countries, the rating system is different (not (R+M)/2). Their 91 could be our 87 here. Their 97 is close to our 91. Make sure you know that when you travel abroad.
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