I understand that the JK takes regular gas (approximately 87 octane), but is it advantageous to put is higher octane levels (premium in the 90's? Thought higer octane would be better for performance and engine. Got conflicting information that higher octane is not good for the engine - confused?? Any thoughts out there?

 

no its not good for your engine, the jk engine is tuned to run at 87 octane and you will get the most performance, and most power out of 87. if you put 93 in ur jeep the gas burns hotter and actually hurt ur jeep since ur jeep is not tuned to handle that. just stick with 87 in-order to burn 93, you would need to get a power programmer, and do a few things to ur engine in-order to get the most power out of the gas you are putting in there, but then you wont be able to run 87 again.

 

its designed and tuned for 87, running anymore without a tune for more is a waste. Even a tune is only going to add timing to take advantage of the octane...not 'huge' gains.

Plain and simple. Octane is anti-detonation rating. The higher the octane, the higher combustion temperatures/compression can be allowed. If you aren't changing the timing or compression ratio, it won't do you any good.

 

It won't hurt anything running higher octane alone, just no benefit. Higher octane burns cooler, which aids in preventing preignition. Higher octane and a tune for it could result in higher combustion temperatures, but not to the point that it will "hurt ur jeep".

 

Higher octane is a waste of money unless you make changes to the engine that will benefit from it, i.e. increasing compression or advancing the ingition timing with a programmer.
I know the Hypertech can program your ingition for running on premium gas, so I'm sure the other brands can also.

 

The owners manual specifically says you can damage the engine by using higher octane fuel.

I don't have my manual to look up exactly what it said but I looked this up online from an online owners manual:

 

Ok guys, This is from a racing perspective and experience.

If your stock, run the low 87 octaine fuel. Your timing maps and compression is tuned to not detonate at this octaine.

The higher Octaine number the more it resists pre ignition. It other words, its harder to ignite the fuel and the fuel burns slower than a fuel with a lower number. You want to use the fuel with the lowest number you can with out causing pre ignition or knock or detonation, all the same event and this will give you the best performance.

Defination of Knock is when your fuel pre ignites or "goes off" before the spark tells it to. In other words, your fuel is injected into the cylinder and it encounters a "hot spot" from either a worn motor, too high compression, dirty valves or what ever and that hot spot causes the fuel to combust at the wrong time. This puts stress on the piston as its still in the compression stroke and this puts a lot of load on the crank, rod and bearings. If this happens long enough, often enough you will have engine failure.


Where most peoples confusion comes from with high octaine fuels is that they see many performance and race engines using it so it must be better for all applications but thats not true. High performance engines use this slower burning fuel to take advantage of other performance enhancing things with a much improved margin of safety to prevent knock. High performance engines gain that performance by either raising compression, advanced timing or pressurised manifolds through super charging or turbos and all of the above. These all raise cyllinder temps and increase the likelyhood of a regular fuel pre igniting. I could go into much more detail but that is the gist of the basics... Most of these high performance engines also have a much more beefy bottom end including stronger rods, bearings and cranks with very good fastners to hold it all together under these much higher cyllinder pressures.

People running your jeeps hard with an aftermarket tune probably should run a little more octaine just to be on the safe side but if your stock stay with the cheap fuel and you will be fine. If you have an ability to plug into your computer and monitor the knock sensor then you could try different fuels and if no knock you are fine.

Hope that all makes sense.

 

If you are not having preignition issues then the anti-knock advantages of a higher octane fuel are simply not needed. Don't waste your money....

 

nothing in what you quoted from the manual says anything about damage. It says poorer performance (as in not optimum) and no benefit. Zero wording about damage

 

From 2008 manual

FUEL REQUIREMENTS
All engines (except 5.7L engines) are designed
to meet all emissions regulations
and provide excellent fuel economy and
performance when using high quality unleaded
“regular” gasoline having an octane
rating of 87. The use of premium
gasoline is not recommended. Under normal conditions,
the use of premium gasoline will not provide a benefit
over high quality regular gasoline, and in some circumstances
may result in poorer performance.

Light spark knock at low engine speeds is not harmful to
your engine. However, continued heavy spark knock at
high speeds can cause damage and immediate service is
required.
Poor quality gasoline can cause problems such as hard
starting, stalling and hesitations. If you experience these
symptoms, try another brand of gasoline before considering
service for the vehicle.

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