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Discussion Starter · #1 ·
Pardon my ignorance but I am hoping perhaps someone more knowledgeable could help address my question about which gas octane to use on a V6 pentastar.

So the manufacturer states that the RAM Rebel v6 pentastar needs 87 octane. Now I fed my other cars (all v8's and others with turbo's) 91 octane only. This will be my first car that the manufacturer states that can take 87 octane. So i am looking forward to "cheaper" gas.

However, I am not sure if fueling the truck with 87 octane vs 91 octane really matters. Should I fed it 91? Will it be better for the engine in the longer run? Can someone kindly advise and give their opinion on what is going to be best for my truck.

I have yet to have my truck arrive. It's on a truck and ETA is March 8th.
 

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Most of today's engines are designed to run fine at lower octane. You might get slightly better gas mileage from higher octane, at the cost of increased wear on the engine from greater pressure, and at the higher cost of fuel. 91 octane runs around 30 cents per gallon higher than 87. That's around 20-30% difference at the pump. Average mileage increases by about 1-2mpg. That's 5-10%. So you're paying double the cost that you might save on fuel economy. Now factor in the greater wear and tear.

Simple math.

You will find guys all over the place on this. Some are religious in their beliefs that higher octanes are better. Well, they are, for engines designed for them. For engines designed for lower octane, they're not.
 

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Most of today's engines are designed to run fine at lower octane. You might get slightly better gas mileage from higher octane, at the cost of increased wear on the engine from greater pressure, and at the higher cost of fuel. 91 octane runs around 30 cents per gallon higher than 87. That's around 20-30% difference at the pump. Average mileage increases by about 1-2mpg. That's 5-10%. So you're paying double the cost that you might save on fuel economy. Now factor in the greater wear and tear.

Simple math.

You will find guys all over the place on this. Some are religious in their beliefs that higher octanes are better. Well, they are, for engines designed for them. For engines designed for lower octane, they're not.
no no no no. higher octane does not increase gas mileage and it does not increase "pressure" and cause greater wear. some fuel stations have less ethanol in their premium selections and better gas mileage can be obtained with lower or no ethanol fuel.

higher octanes are simply more resistant to knocking. if the engine does not require it or if it is not tuned around it there is no reason to run a higher octane.
 

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One of the reasons why you might need it is when running system cleaners, aside from that it's a big waste of money if not required.
 

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no no no no. higher octane does not increase gas mileage and it does not increase "pressure" and cause greater wear.
Okay, I've always been taught this was the case and never questioned it. Trusted too many buddies, I guess. I looked it up and indeed you're right, both of these are myths. My bad for propagating them.

The rest of what I said stands, though.
 

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I have run a LOT of 87 octane in my 2008 Charger Daytona.. I have 372,000km on that car and there have been no major repairs other than needing swaybar endlinks constantly..

I do put 91 in once in a while but it really isn't necessary. If you are not standing on the throttle I can't see you even having issues with knock.. knock sensors on these cars is really good as well, it would pull timing pretty fast.. (in addition to running 87, I also got some bad gas once.. knock sensor registered pretty high LT knock that cleared as the fuel was diluted and ran through the system.. )

Users manual states:
89 Octane Recommended - 87 Octane Acceptable,
0-15% Ethanol.

So as long as you don't do something goofy like put in Diesel or E85 you are fine.

:)
 

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Discussion Starter · #8 ·
Fellas,

This is the tech spec on the v6 pentastar. Pentastar Engines: Overview and Technical Details

The key information, for me, in the link as it related to our discussion is: "Despite the impressive gains in power, the engine is designed to run on regular unleaded fuel with an octane rating of 87. The engine also can run on E85 blended gasoline."
 

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Fellas,

This is the tech spec on the v6 pentastar. Pentastar Engines: Overview and Technical Details

The key information, for me, in the link as it related to our discussion is: "Despite the impressive gains in power, the engine is designed to run on regular unleaded fuel with an octane rating of 87. The engine also can run on E85 blended gasoline."
Yeah, I saw that after, I was looking at the manual for the 5.7.. I never think about e85 since I have NEVER seen a gas station that has it here in Southern Ontario.. :)
 

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I've had two Pentastar engines in Jeep Wranglers.

I actually saw better fuel economy on 87 vs 89 or 92.



I run Shell 87 in the 5.7 Rebel too, with no impact to performance or economy.
 
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