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Gas Octane vs. Mileage and Performance


GordonZoo

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So I'm reading we can use just about any gas in our 3.5 Navi depending on your needs. I was wondering what you run in yours vs. mileage and any noticeable performance. I've always been told you should always stick to the same octane and even keep to the same gas station as you car gets used to it. Now I'm reading with this animal, throw anything in there and it will move this beast.

:peelout:

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Try to use top tier - specific brand doesn't matter as much as using a busy station that doesn't have gas sitting in the tank for a long time.

 

You will get a bit more power and slightly better mpg with premium but it's not nearly enough to offset the cost. I'd only use it when towing especially on hot days.

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For the record I have a chemistry degree.... That being said.... octane rating in gas has absolutly nothing to do with quality. This is a huge misconception. It is strictly based on the compression ratio of the engine. Higher octane is needed for high compression engines to prevent pre detonation in the combustion chamber. As gas compresses it can ignite on its own before the spark plug fires. This is what causes knock. A higher octane prevents this from happening. This is why to always use what is recommended in the manual. Using a higher octane more than what the engine calls for would work counter productive to engine performance and in gas mileage, not to mention the waste of money for premium gas. New engines can run on lower octane than what they are rated for because the computers can detect knock and they can retard the timing of the spark plugs to compensate. This is done at the expense of performance and MPG though. our new navies say 93 for max performance so I would stick with that. Besides, cant really argue about trying to save money on gas when we are driving a 90K truck... :victory:

 

So bottom line.... read the owners manual and follow directions.. :)

 

 

As for ethanol... For post 2000 and up cars not so much an issue since they were designed to use up to e15 ethanol in gas. However if you do have access to no ethanol, then filler up... Good luck finding it though...

Edited by god503
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The misconception about quality differences with premium goes back to the 70s and 80s when companies put more detergents in Premium than they did in Regular. That could still be the case with some brands today but it's the additives that make the difference not the octane level.

 

I use top tier gas which is guaranteed to have the right additives for best protection.

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the additives usually are based on the brand, exxon, BP etc. bigger name brands usually use the same level of additives across all three grades. However i do know for a fact from a friend of mine that owns an exxon gas station, the premium level gas does get an extra filter at the pump than the other grades.

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The best answer is to run a full tank or two and see. Sometimes MPG suffers dramatically based on YOUR particular driving style and fuel. Ecoboost engines run best with higher octane and no ethanol. However, when you put pen to paper and calculate it, it might not be worth it for YOUR useage.

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For the record I have a chemistry degree.... That being said.... octane rating in gas has absolutly nothing to do with quality. This is a huge misconception. It is strictly based on the compression ratio of the engine. Higher octane is needed for high compression engines to prevent pre detonation in the combustion chamber. As gas compresses it can ignite on its own before the spark plug fires. This is what causes knock. A higher octane prevents this from happening. This is why to always use what is recommended in the manual. Using a higher octane more than what the engine calls for would work counter productive to engine performance and in gas mileage, not to mention the waste of money for premium gas. New engines can run on lower octane than what they are rated for because the computers can detect knock and they can retard the timing of the spark plugs to compensate. This is done at the expense of performance and MPG though. our new navies say 93 for max performance so I would stick with that. Besides, cant really argue about trying to save money on gas when we are driving a 90K truck... :victory:

 

So bottom line.... read the owners manual and follow directions.. :)

 

 

As for ethanol... For post 2000 and up cars not so much an issue since they were designed to use up to e15 ethanol in gas. However if you do have access to no ethanol, then filler up... Good luck finding it though...

Some anti-knock sensors retard spark timing. Some just add more fuel.

 

That and with the advancement in computers, higher octane is managed by the engine.

 

You will find many domestic engines actually run better on the higher octane. Lower octance being recommended for cheap owners.

 

On ethanol, no conversation is complete without mentioning moisture.

Edited by J-150
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Thanks for the input. I think I got what I needed. It's OK to run any Octane and change time to time depending on needs. I don't have an option to opt out on ethanol up north though. On a similar note I remember back in the day running Leaded gas in my car and getting a heavy boost in performance. No telling what that did to our health over the years. Same with Corn fields, No telling what the environmental impacts are making Ethanol vs. the "cleaner air" we get from it. That's a whole other topic.

I can't wait to get our Navi and have a few road trips. I will try 93, 89 and 87 to see it there are major performance difference and choose from there. No towing needed as I have a Diesel Ram for that. We've owned a 97 Exp, 2007 Navi and now a 2019. Nothing rides better for long trips IMHO. I'll get back with some numbers in February once I get some miles in.

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How would adding more fuel prevent pre-detonation? If anything it should make it worse.

 

I think all computers retard timing to avoid knock.

 

Too lean of a mixture can cause detonation. Adding more fuel can stop it. However, according to the tuners of Ford turbo engines, retarding the timing is how stock Ford PCMs avoid knock. When we were tuning my Continental, several adjustments were made to the spark and A/F ratio to obtain maximum efficiency with no knock and as much timing advance as we could safely run. We did add some additional fuel at WOT compared to stock which allowed additional timing and boost without knock.

 

Livernois has said that the difference between 93 and 87 octane fuel is a 5% loss in peak HP on the gen 1 ecoboost 3.5....and even more in low to mid-range RPM. That may be different on the new generation like in the Navi.

 

By the way, most tuners LOVE ethanol due to the cooling effect as well as the increased octane. The fastest tuned SHOs and other ecoboost vehicles run heavy mixtures of ethanol. Higher mixtures above 30% require a more potent fuel pump. The Coyote Mustangs love ethanol as well when tuned for it.

Edited by brucelinc
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Livernois has said that the difference between 93 and 87 octane fuel is a 5% loss in peak HP on the gen 1 ecoboost 3.5....and even more in low to mid-range RPM. That may be different on the new generation like in the Navi.

 

 

So 10hp on a 200 horse engine, 15hp.on a 300 horse engine. Not peanuts.

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So 10hp on a 200 horse engine, 15hp.on a 300 horse engine. Not peanuts.

 

They were talking specifically about the 365 HP Ecoboost engine in the SHO. I think they were talking about HP at the wheels and not the crank. As I recall, a stock SHO makes around 290 HP at the wheels on 93 so around a 15 HP loss. It was less than 5% at low RPM but more than 5% in the mid-range and then 5% at peak.

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Since we started talking about performance of the new Navi... would it have really killed ford to give the new navis a twin intake and dual cat back exhausts? I mean for a 90 K truck all we get a is a fart can in the back and a single intake feeding twin turbos? This engine supposedly gives out 450 ponies as is. Im sure it would have gone north of 500 with a little more TLC on the intake and exhaust. They even plan on dual exhaust for the aviator. At least do it for the looks!!!

Edited by god503
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