tburk49760

Anyone have any real world data regarding weather or not the 3.8 is able to change timing enough to gain any measureable mpg or hp burning premium vs regular fuel? In my mind, it seems as though it should be able to advance the timing using the knock sensor or other sensors and retard timing for lower octane fuel. Maximum safe advance = maximum efficiency and therefore power right???

vw73182

if your engine calls for premium fuel you should run premium fuel unless you like cause unnecessary stress to your engine.

highoctane

Your engine has a max commanded spark programed in the stock tune on every OBD2 vehicle. Part throttle ignition timing changes based upon how the vehicle is being driven, operating temp, etc, but WOT timing does not change unless altered by an aftermarket tune or if the engine is overheating.

Lorrel

Have no idea what you're talking about, however I do know the JK is listed to use 87 grade. Since the 3.8 has been around for many years, and has never been a high performance engine, and most likely never will, what do you expect to gain by using high test fuel. Do you think the electronics utilized in the engine to keep it running correctly on a certin octain fuel, will somehow make it better by using a higher octain.
I do believe the engine was engineered to run on a certin octain fuel and the sensors were designed to maintain efficiency using that fuel. This was most likely based on the cubic inch, bore and stroke, fuel to air ratio, compression ratio, and exhaust outlet. The sensors, although high tech, are not of the learning and addapting, technology but rather just an I/O matrix, and are not going to enable the engine to come alive. Those days are not yet here.
I believe using a high test fuel in this engine will do nothing more that get deeper into your pocket and may do more harm then good.
I may be wrong though.

davidwm71

It is actually stated in the manual that using high octane fuels may damage the engine.

tburk49760

well that makes absolutely no sense what so ever... damage it??? perhaps I am too dumb... I was hoping someone had actually tried premium and documented the mpg differences if any... I will try to do it myself. wouldn't take much of an increase in mpg to offset the additional cost. regular is 2.14 and premium is 2.35 at the moment so a 10% increase in mpg would make it even and any more would be a beautiful thing... any hp increase would be a major blessing... wish me luck...

Adam3612

In the manual it says using anything above the recommended 87 Octane may cause engine knock and permanent damage to your engine. Fill your boots tho, I just cant see it making any difference.

4x4jkx

I ran premium a couple of times. I got no increase in mileage. It's not worth them money. Plus since I now know it can harm the JK I ain't touching the stuff.

arkain04

Having worked at commercial pumping stations, I know when the fill a truck with 93 the line has either been flushed with water to the waste tank or you are getting 87 flushed to the fuel truck as well.

So at best you put in 93 and really are getting a mix of 87 or 89 with it. So it is not really 93.
At worst you get a water residual in the line that is flushed into the truck.
then your reliant on your stations placement of their siphon or pump location on the tank to not get water intrusion, also relying on their filters at the station and we all know they change those out often Right??

That being said I always run 92 in mine. Have never had a problem I feel better throttle response on this than lesser octane. I have seen no real judgeable (if that is a word) difference in MPG though. I have also not seen or heard any knocking or temp difference.
The higher the octane the cleaner the fuel the less engine deposits, ie valves etc.............

Blue

The are are only a few reasons for high octane fuels. One is higher engine compression. When I am towing with one of my other rigs in the summer, I sometimes use it because it will have cooler exhaust temperatures. Out side of that, there is no real advantage other than spending more money on gas.