Especial86

iTrader: (1)

93 octane is more stable in higher temperatures than 87.. On a hot day you might actually find a need to run a higher octane if the IAT temps are running hot enough to cause knock/detonation.

A dirty carbon covered engine might also benefit thanks to detergents added to 93.. Carbon can actually soak up fuel like a sponge, and cause hotter combustion temps from a leaner mix..

Octane rating is essentially a measure of resistance to heat. The hotter your air temperatures are, the higher your octane requirement will be.... This is why I will agree that summer time is actually a good time to run a higher octane. If you feel more power, or better milage, odds are that your engine has been pulling timing, because your knock sensors are listening to detonation..
Knock sensors are basically just microphones.

On boosted, supercharged and turbocharged motors, boost is actually a measure of restriction. That restriction is due to compressing air, and compressed air heats up as its compressed, and expands. Compressed air heats up just like it does in a non (FI) forced induction motor that relies solely on the compression stroke of the piston.
FI motors are heating up the ambient air before it even hits the cylinder, so the air is heated to an even greater temperature once the cylinder is compressing the boosted (compressed) air and fuel mixture. So when 93 is mixed with the already hotter FI air, it remains more stable to allow for the timed ignition event from the spark plug to burn it...

So yes, 93 octane on a hot day, on a hot motor, will be more stable. The knock sensors will pull less timing, and yield you more power, and better efficiency..

Is it a myth that 93 octane is better than 87?
Yes.. It's not better, it's just more stable than 87 under higher temperatures..

Manufacturers do add more detergents to it, and that does help. But they also misguide consumers with the terms:
"regular" for 87
"Super" for 89
"Premium" or "ultra" for 93 and 91
If you open your eyes to our nearly pure consumption based economy, you will see these tricks of the marketing trade everywhere....

There is definitely a need for multiple octanes, but it has nothing to do with power, it's about stability..

Summers22

iTrader: (2)

^^The reason being for the stability is 87 octane has 10% ethanol. 91 or 93 octane does not. That is the reason I run 91 octane, performance sucks with 87 due to the ethanol content. Well that, and I have my timing bumped a degree!

ford4wd08

??? All fuel grades have 10% ethanol. I do see offerings of 93 octane that is 100% gas, but it is at a much higher price, around 3.50 a gallon now. Maybe it depends where you are in the country???

screamineagle

^^The reason being for the stability is 87 octane has 10% ethanol. 91 or 93 octane does not. That is the reason I run 91 octane, performance sucks with 87 due to the ethanol content. Well that, and I have my timing bumped a degree!
Unless you live in Missouri, your sadly mistaken sir.....

gdfishwell

Here around Galveston Texas, ALL the gas regardless of the octane rating contains a minimum 10% ethanol. I would have to drive well over 100 miles to get pure gas.

ford4wd08

Misread. Disregard.

Summers22

iTrader: (2)

Where I am in Kansas, 87 octane has 10% ethanol, 89 & 91 are pure.

ol'skool

Here in ky, it's hit or miss. Some stations have ethanol in all grades, some only on 87. Occasionally....you'll run across one that is pure gasoline on all grades, but that's getting to be the exception rather than the rule.

It should be noted I live in KY's largest city, there's plenty of opportunity to find just the right gas. However, where I grew up....you have basically 3 options and all of them are crap.

HeathMc

Same here in Idaho on the hit and miss. Couple of stations offer 0 ethanol in all their fuels (and they charge a premium) and a couple have it advertised that premium only has no octane. I just went to running only chevron regular and my 5.4 seems to like that.

mmdutcher

My test begins today. I filled up with some premium gas (91 octane).

Question though... if there is ethanol in the gas, then would that be or should that be posted on the pump?