No,you are correct, the other guy is WRONG.

 

(patiently waits for the flame)

 

Do a little research on octane through credible sources. There are a lot of misconceptions and false info on this subject. If anything, you can start with 87and if it knocks, try 89, then 91. If it isn't knocking, which it won't, you are OK with the 87. BTW, don't let the screen name fool ya, I'm actually a ME.

 

Being an ME doesn't mean you know any more than the short bus kids about combustion or chemical engineering as it relates to fuels and their makeup and function. Sorry, I just couldn't resist since you pointed out your schooling.

I thought octane was supposed to help resist pre-ignition and/or detonation. I'm not really sure if I even know what pre-detonation is.

With all that said, I agree with you. If you do not have audible detonation, you are likely ok. Some things can trigger it when you "run on the edge", like a hot day, or altitude changes. If you already have a full tank of the cheap stuff, this could present quite a problem. I suppose a good bottle of "boost" might save you.

I have two motorcycles that allegedly "require" high octane fuel. I run both on 87 octane (the calculated value on the pump) and they both run fine, and have for many thousands of miles. I even have reasonable records that indicate that one of them gets better fuel economy on the cheap stuff. On other vehicles that I have owned that did have detonation problems, using higher octane fuel did not help or change the situation.

If you have alleged "credible sources" please provide them in name, or with links if they don't violate the rules here. The SAE is a good source, but they don't allow free use of their data.

 

fine don't let the screen name make you think I am some dumb grunt.
I am a Navy corpsman with a Dell and time


octane or octane ratings

The octane rating is a measure of the autoignition resistance of gasoline (petrol) and other fuels used in spark-ignition internal combustion engines. It is a measure of anti-detonation of a gasoline or fuel.

Octane number is the number which gives the percentage, by volume, of iso-octane in a mixture of iso-octane and normal heptane, that would have the same anti-knocking capacity as the fuel which is under consideration. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90.
This does not mean, however, that the gasoline actually contains these hydrocarbons in these proportions. It simply means that it has the same autoignition resistance as the described mixture.

Ok, now that we have that covered, lets do some basic 4 cycle internal combustion info

Detonation: A spark from the spark plug starts normal combustion. The flame travels across the combustion chamber rapidly and smoothly until all the fuel is consumed. Abnormal combustion occurs when part of the fuel/air mixture ignites spontaneously and burns very rapidly, causing the pressure to rise suddenly.
As the piston is being forced upward by mechanical action of the connecting rod, the pre-ignited (NOT pre-ignition) explosion will try to force the piston downward. If the piston can't go up (because of the force of the premature explosion) and it can't go down (because of the upward motion of the connecting rod), the piston will rattle from side to side. The resulting shock wave causes an audible pinging sound.

Pre-ignition: Note: Pre-ignition usually leads to detonation; pre-ignition and detonation are two separate events
The onset of combustion before the spark plug fires. This is generally caused by some type of glowing ignition source such as a hot exhaust valve, too-hot spark plug, or carbon residue. Or simply the plug firing too soon in the compression stroke.

Getting rid of Pre-ignition without changing the octane of your fuel:
colder air
cam overlap

and lastly, TIMING.

oh wait..another lesson.

Timing:
when at what time in the stroke the sparky plug thingie goes "spark". Sparky before TDC is "advance" sparky after is "retard"

Theoretically the correct time for the spark the piston should be at TDC, as far up as it can go compressing the air/gas mixture on the compression stroke. This means that ignition timing is at 0° with no advance or retard. However, in real life the spark goes off before this to allow for a combustion lag time delay and for the controlled burn to travel across the combustion chamber.

You ADVANCE timing for more power to a point because then it causes pre-ignition/detonation, You RETARD it to help not.

The higher octane the fuel the more you can advance without fear of pre-ignition because the fuel is not "right there OMFG!! ready to burn by itself"

The chip advances the timing to give more power (in addition to other things)




sooooo....in closing:
Putting lower octane fuel in a chipped Jeep is retarded as you are not gaining the power promised and you should have just save the money and got the lesser stage chip because you are too cheap to run the higher octane
Also your idea of "well if it don't ping you be fine" is the most retarded circular logic I have seen in a while. Its a friggen computer controlled engine, it will retard the timing so much to STOP the pinging that it will run like ass. Its not like tuning a carb. What do you think the ping sensors are there for.

I will break it down:
You buy blingity chip and install
You run crap gas
ping sensors detect detonation
computer retards timing
you lose power back to "normal"
computer is happy cause no ping, it don't care you have no power.