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deeje1

Fuel Prices

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If I was making a quick stop in cold weather, especially shortly after start up, I'd idle my Cherokee but in those conditions the start....stop....start......................................stop cycle seemed to hurt the mileage (as well as the warming of the truck's interior) when compared to a start....idle......................................stop cycle.  In the current weather or longer drives before shutting down, that does go away.

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I think its laughable that anyone thinks they will get more power from gasoline...

 

I'm with you, except that is is sad that there are still people out there who think that higher octane gives you more power. Oh well.

 

Besides, it is never wrong to invest more into something that is healthier, or serves other benefits, like Ethanol does.

 

Greetings!

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I think its laughable that anyone thinks they will get more power from gasoline...

 

I'm with you, except that is is sad that there are still people out there who think that higher octane gives you more power. Oh well.

 

Besides, it is never wrong to invest more into something that is healthier, or serves other benefits, like Ethanol does.

 

Greetings!

 

Actually in certain newer cars, the manufacturer will recommend a higher octane and require a lower octane for exactly that reason, it makes more power on higher octane. The Scion FRS is one recent example since it recommends 93 AKI but only requires 91. But I also know the Mazda Skyactiv engines were built for higher octane and then detuned for the US regular octane.

 

Higher octane means a little better fuel economy too, but only when higher octane is recommended or required.

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Higher octane does not give you more power.

 

It is the engine which can utilize the higher octane. When driven with lower octane, you loose power, but it never works the other way around.

 

The higher the octane number, the more compression the fuel can withstand before detonating. Higher octane ratings correlate to higher activation energies.

 

It is like the cited 105 octane rating for E85, which is incorrect. This number was derived by using ethanol’s blending octane value in gasoline. This is not the proper way to calculate the octane of E85. Ethanol’s true octane value should be used to calculate E85’s octane value. This results in an octane range of 94-96 (R+M)/2. These calculations have been confirmed by actual-octane engine tests.

 

Greetings!

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It is the engine which can utilize the higher octane. When driven with lower octane, you loose power, but it never works the other way around.

 

The higher the octane number, the more compression the fuel can withstand before detonating. Higher octane ratings correlate to higher activation energies.

 

I'm only talking about new engines that are detuned to run lower octane in the US, such as some imports, but have a higher recommended octane rating. Not higher octane fuel alone.

 

Edit: For example from the manual for the 2012 Focus (4e)

 

Octane recommendations

Your vehicle is designed to use

“Regular” unleaded gasoline with a

pump (R+M)/2 octane rating of 87.

Some stations offer fuels posted as

“Regular” with an octane rating

below 87, particularly in high altitude areas. Fuels with octane levels

below 87 are not recommended. Premium fuel will provide improved

performance.

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A lot of the newer engines run a higher compression ratio than is optimal on 87 octane, and will pull ignition timing as necessary.  Running higher octane in these engines will give you smoother running, a bit more power, and higher mileage, or at least a more efficient conversion of BTU's to work.  Ethanol helps in this regard.

 

As per E85's octane rating, the AKI might only be 94-96, but there is a large difference between the RON and MON, unlike normal gasoline.  In an actual engine, it acts better than most race gas.

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If ethanol's octane and ability to withstand preignition/spark knock is only the same as 94 octane gas, then my engine is going to have a very bad time. 13:1 with iron heads is far too high for 94, on gas with that octane it would rattle itself to death and probably knock the upper rod bearings flat. The 4.181" bore does not help the situation for spark knock either, because a larger bore is more sensitive than a smaller bore.

 

Its true that the test doesnt show accurate results, but the reality of it is ethanol can withstand far more compression and ignition lead than gasoline can. You have to get into some very expensive race gas to get close to what ethanol can handle easily.

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A lot of the newer engines run a higher compression ratio than is optimal on 87 octane, and will pull ignition timing as necessary.  Running higher octane in these engines will give you smoother running, a bit more power, and higher mileage, or at least a more efficient conversion of BTU's to work.  Ethanol helps in this regard.

 

As per E85's octane rating, the AKI might only be 94-96, but there is a large difference between the RON and MON, unlike normal gasoline.  In an actual engine, it acts better than most race gas.

 

That appears to be how the Pentastar V-6 works too, (the version of the 3.5l V-6 in the Intrepid R/T was like that too, but just for use with gasoline), and Dad even thinks that with these motors being a VVT  engine, they might have it programed to alter valve overlap based on what the octane or in my case type of fuel being used.

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If ethanol's octane and ability to withstand preignition/spark knock is only the same as 94 octane gas, then my engine is going to have a very bad time. 13:1 with iron heads is far too high for 94, on gas with that octane it would rattle itself to death and probably knock the upper rod bearings flat. The 4.181" bore does not help the situation for spark knock either, because a larger bore is more sensitive than a smaller bore.

 

Its true that the test doesnt show accurate results, but the reality of it is ethanol can withstand far more compression and ignition lead than gasoline can. You have to get into some very expensive race gas to get close to what ethanol can handle easily.

 

I agree but the octane rating is correct even if it doesn't necessarily translate to the real world. Just ask corey how his turbocharged high compression engine is doing. ;D

 

Or even better check this out. Stock Toyobaru engine but with a custom 93 AKI vs E85 tune.  8) (Blue is stock which is 91 AKI Required, Red is 93 AKI custom, and Green is E85).

post-1671-138947095153_thumb.jpg

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Keep in mind that the motor octane test protocol is appropriate for gasoline but not alcohols. The test requires the intake air/fuel temps to be elevated to a high level. What do we know about alcohols? - -- they get their knock resistance from the cooling effect on vaporization. To have to heat this vaporized mix for the official motor octane test is to counteract the very property that gives ethanol (or any alcohol type) it's high resistance to knock. This is why you see everything from the crazy low 94 (motor-not r+m/2) E85 ratings to 105 or to 119 on pure. One race gas supplier did a lot of lab testing on their E85 blend and conservatively put their mix at 112. 

 

Octane by it's nature is only about gasoline (it once was the fossil component of gas that was being compared against).

 

A better measure is to look at allowable compression ratios that drag racers or other performance guys typically use it at. Most common E85 race engines in bracket drag are 13 or 13.5:1 while a few have even reached 16:1 with the right cam/head setups. Pump grade E85 typically replaces 110-112 octane race gas. Some racers blend their own to a consistent spec and doing so replace an even higher octane race gas such as 114.

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