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Our 2012 Prius recommends using the regular stuff. We’ve never really used the lower grades, unless for some reason the gas station was out of premium. Some people have experienced Prius cold start engine knock possibly due to engine crud being pushed back into the engine via EGR. Solution for them, oil catch can. Not us, at least so far....

Can anyone say Anti-Knock Index? (AKI)
 

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My 2017 5.3 Silverado recommends 87. If I give it 87, the mileage is very dependent on my driving style. Could go 14, could go 21. But if I give it that ethanol free 92 that I run in my smart, it is more like 17-22. This tells me that even in a vehicle where the 87 is recommended, the knock sensor is actively compensating for it.

In the smart, the knock sensor and timing are set up to deal with the shortcomings of 91 octane, and a combination of a heavy foot, and cheap gas can outrun the car’s ability to fix the situation.

Hypermiler? Go 87. Light footed commuter? Go 87. The rest of you are screwing up your cars.
 

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WHEN does beating a Dead Horse begin to stink???

https://fueleconomy.gov/feg/octane.shtml

Because of the propensity for smart 451 engines to have head/valve issues, if I were to trade down to a lower octane I'd only buy from Top Tier retailers. Typically their gas has a higher-percentage of detergent additive from that required by the EPA standard.

https://www.truecar.com/blog/2011/03/03/premium-vs-regular-gas/

DISCLAIMER - even with a 50 cent R-P spread, I will gladly continue to pay the $4 per tank "premium."

But, at the end of the day - it's YOUR car . . .
 

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WHEN does beating a Dead Horse begin to stink???

https://fueleconomy.gov/feg/octane.shtml

Because of the propensity for smart 451 engines to have head/valve issues, if I were to trade down to a lower octane I'd only buy from Top Tier retailers. Typically their gas has a higher-percentage of detergent additive from that required by the EPA standard.


DISCLAIMER - even with a 50 cent R-P spread, I will gladly continue to pay the $4 per tank "premium."

But, at the end of the day - it's YOUR car . . .
If you run a lower octane , you will likely have head and valve problems due to detonation under load. The detergent has nothing to do with detonation, Its the compression ratio of the engine that requires the higher octane. Use premium grade fuel 91 or higher or suffer the consequences.
 

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I used 87 octane once, while in Iowa. 91 wasn’t available. I use premium in all my vehicles that call for it. Nothing less.
 
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