mmmm, I've never used anything higher than 87 in any car or truck. I'd drop Octane booster ($2 x 2/ treat 14 gallon per bottle) in before I put in 25 gallons of gas that's .50 more expensive.

On that note, let's all stop buying the mid grade (yes I hear its Hemi approved) so gas stations will eliminate it so gas prices drop by 30%.

Then we can all go buy the dirty fuel in our diesel trucks (better for the environment anyway).

I will tell you this. They tune for octanes for peak performance. I can't tell the dang difference and I drive with one ear to the block all the time.

 

Lets clarify, 87 will work. It will burn and run the engine. But when you are looking at engine tolerances and compression ratios and piston knock (again - all geared towards tuning) you will see the differences.

 

just a heads up though- if you run too low of octane rating if can pre-detonate(piston knock--basically the heat in the cylinder is igniting the fuel/air mixture- before the spark plug) and this can blow holes in the top of your pistons--- quite bad stuff!

 

so higher the octane rating-- the harder it is to ignite

 

89 until i started modding. Now 91 period.

 

I have a 35 gallon tank, or 135 lt. Its not breaking me to run mid grade. Highway drives, or towing I run 92 octane.

day to day stop and go, 89 octane.

 

No, it does not. Please read these to help you understand.

Octane
Octane Rating
Engine Knocking

The octane rating is a measure of the resistance of petrol and other fuels to autoignition in spark-ignition internal combustion engines.

Octane rating does not relate to the energy content of the fuel (see heating value). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where octane is raised by blending in ethanol, energy content per volume is reduced.

It is possible for a fuel to have a Research Octane Number (RON) greater than 100, because iso-octane is not the most knock-resistant substance available.

Research Octane Number (RON)

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

Motor Octane Number (MON)

There is another type of octane rating, called Motor Octane Number (MON), or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load as it is done at 900 rpm instead of the 600 rpm of the RON[2][3]. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally, fuel specifications require both a minimum RON and a minimum MON.

Anti-Knock Index (AKI)

In most countries, including all of those of Australia and Europe the "headline" octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, like Brazil[4], the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2.

Difference between RON and AKI

Because of the 8 to 10 point difference noted above, the octane rating shown in the United States is 4 to 5 points lower than the rating shown elsewhere in the world for the same fuel. See the table in the following section for a comparison.

It might seem odd that fuels with higher octane ratings are used in more powerful engines, since such fuels ignite less easily. However, an uncontrolled ignition is not desired in a spark ignition engine.

A fuel with a higher octane rating can be run at a higher compression ratio without causing detonation. Compression is directly related to power and to thermodynamic efficiency (see engine tuning), so engines that require higher octane usually deliver more motive power and do more work for a given BTU or calorie of fuel. Engine power is a function of the fuel, as well as the engine design, and is related to octane rating of the fuel. Power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. When the throttle is partially open, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than when the throttle is opened fully and the manifold pressure increases to atmospheric pressure, or higher in the case of supercharged or turbocharged engines.

Many high-performance engines are designed to operate with a high maximum compression, and thus demand high-octane premium gasoline. A common misconception is that power output or fuel mileage can be improved by burning higher octane fuel than a particular engine was designed for. The power output of an engine depends in part on the energy density of its fuel, but similar fuels with different octane ratings have similar density. Since switching to a higher octane fuel does not add any more hydrocarbon content or oxygen, the engine cannot produce more power.

However, burning fuel with a lower octane rating than required by the engine often reduces power output and efficiency one way or another. If the engine begins to detonate (blow up), that reduces power and efficiency for the reasons stated above. Many modern car engines feature a knock sensor – a small piezoelectric microphone which detects knock, and then sends a signal to the engine control unit to retard the ignition timing. Retarding the ignition timing reduces the tendency to detonate, but also reduces power output and fuel efficiency.

Most fuel stations have two storage tanks (even those offering 3 or 4 octane levels), and you are given a mixture of the higher and lower octane fuel. Purchasing premium simply means more fuel from the higher octane tank; the detergents in the fuel are often the same.

 

So, to answer the OP's Q, does octant matter? Yes it does. But again, it depends on what you are trying to get out of your engine and depends on tuning capabilities.

If yuo read nothing but "However, burning fuel with a lower octane rating than required by the engine often reduces power output and efficiency one way or another. If the engine begins to detonate (blow up), that reduces power and efficiency for the reasons stated above." you can understand why it matters.

What do you think happens to your engine internally when you have this knock? What do you think happens when internal components are overloaded from pressure and pre-detonation? What do you think happens to your power output and average MPG?

 

In general, if your engine is running properly at the lower octane levels, use them.

Your engine will not know the difference between 87 and 93 if it has no problems.

Some engines like the BMW 4.4L automatically slow the timing (and also HP) when you drop octane levels, so if you got bad gas, the car would still be driveable, down to half of the cylinders. I don't think the Dodge does.

 

I have got to politely call BS on this one. YOU may not know, see or hear the difference but your ENGINE does.

Again, if you have a tuner and can look at your PID logs and read the differences in those PID and tuning logs from 87 to 93 you will see a world of difference.

Just because you can run a tank or 87 (or even several) and not have any adverse side affects does not mean your knock sensors dont notice the lesser grade fuel.

Again as and said in port #22, sure it will work but if you truly understand the internals and designs of an engine and blends of fuel, you will know what you can and should use.

And yes, you are right that Dodge Ram PCMs do not auto adjust base spark or other tuning features. Those have to be written to the PCM via custom tuning.