Higher octane for towing?

Rob0381 · **Posted:** Thu Sep 06, 2007 12:05 pm

I was changing my oil yesterday, and was looking up the oil capacity when I noticed something interesting. Under fuel type, it says 87 oct., but when towing with the 3.7, it says to use 89 oct. I thought the octane rating didnt do much for the performance of the KJ. Someone wanna chime in and explain to me why this is? Thanks alot...

BTW, I have an 06.

sleeve84028 · **Posted:** Thu Sep 06, 2007 1:01 pm

I've never switched over octane for towing...

Jeepjeepster · **Posted:** Thu Sep 06, 2007 3:55 pm

It is a good idea to use a higher octane when towing since the engine runs hotter when towing.

It keeps down pinging.

BeepBeepJeepJeep · **Posted:** Thu Sep 06, 2007 5:44 pm

Jeepjeepster wrote:

It is a good idea to use a higher octane when towing since the engine runs hotter when towing.

It keeps down pinging.

I'm not sure how this can be a true statement. If the engine is running hotter because you're towing than you're towing something that's too heavy for the KJ. The cooling system should be able to keep the engine's running temperature the same, no?

sleeve84028 · **Posted:** Thu Sep 06, 2007 5:47 pm

I've never had a problem with pinging while towing.. the computer can adjust the timing just fine for the heavier loads.

SoDakJeep · **Posted:** Thu Sep 06, 2007 6:18 pm

whoa whoa whoa.....haha higher octane is only 89....i run 89 octane its got 10% acl. in it. The highest we have aroudn here is like 91 or 93 depends on where you go....but yea I havent noticed any differance when I ran the 93 compared to when I ran 89 towing....

Rush345 · **Posted:** Thu Sep 06, 2007 7:54 pm

I have not played with different octanes in my Jeep Liberty Sport. But my previous ride was a '95 Dodge Dakota 5.2L 4x4.
Any way I was working across town in Denver 26 miles one way mostly highway, so I had it tuned and set up for the traffic going from on side of Denver to the other it reccomended 91 octane. If I used 91 had great perfomance and power but bad milage, if I ran 89 octane I got better milage but had a noticable hesitation in performance. When I got the Libby and after reading the owners manual found it recomended just regular gas. I figured why fight it go with what it recomends and enjoy the price savings :roll:

Sir Sam · **Posted:** Thu Sep 06, 2007 10:44 pm

BeepBeepJeepJeep wrote:

Jeepjeepster wrote:

It is a good idea to use a higher octane when towing since the engine runs hotter when towing.

It keeps down pinging.

I'm not sure how this can be a true statement. If the engine is running hotter because you're towing than you're towing something that's too heavy for the KJ. The cooling system should be able to keep the engine's running temperature the same, no?

Under higher load combustion temps will increase, yes a good cooling system can compensate for the greater heat needing to be dissipated, and yes the computer can retard the timing when it detects a knock.

However the cooling system has nothing to do with combustion temperatures, and adjusting the timing back means less power. So yes your engine could run just fine without any danger when towing, but running the higher octane could mean that you have more power while towing, especially when under harsh conditions.

You might also find that when running the higher octane while towing your fuel economy might improve to the point that is was financially viable to run slightly more expensive gas, if your engine isnt pinging then the computer doesn't have to: a) retard the timing to prevent pinging, or b) inject more fuel to prevent pinging.

So running mid grade or higher could be beneficial, but I'll let the final determination be up to you.

Alak · **Posted:** Thu Sep 06, 2007 11:00 pm

Octane rating is the resistence to combustion. It doesnt give you more power, but it has the potential for more power if you tune the timing.

When the engine runs hotter and the possibility of pinging becomes apparent, the engine will retard timing if pinging (knocking) is detected. Knocking/pinging is pre-detination. The higher octane fuel allows the engine to combust that chamber percisely when its supposed to. Thus allowing the engine to run proper timing and gain the power it would potentially loose with reduced timing.

In other words:

Only use higher octane if nessesary, or if the engine manufaturer recommends, or requires it.

I used to run 87 all week in my 05' Mazda Miata to work and back. The manual said 91 recommended, but not required. So on the weekend when I raced at the track, I ran 91. There was a noticable difference.

sleeve84028 · **Posted:** Fri Sep 07, 2007 12:12 pm

I'll agree with that.. So to me the octane would come down to

1) How far I'm traveling
2) How heavy the trailer / load is

For the most part my ~500 lbs trailer doesn't do much to the Liberty

JeepJunky33 · **Posted:** Fri Sep 07, 2007 12:56 pm

so would a higher octane improve preformane overall? I dont tow, (nothing to tow) but if I ran a higher octane could I get mpg or performance improvments? or would I just injure my engine?

detroit_doc · **Posted:** Fri Sep 07, 2007 1:32 pm

JeepJunky33 wrote:

so would a higher octane improve preformane overall? I dont tow, (nothing to tow) but if I ran a higher octane could I get mpg or performance improvments? or would I just injure my engine?

In a jeep you wouldn't see any performance benefit, although it won't hurt anything either.

The computer in the jeep is probably not very aggressive as far as advancing ignition and leaning the mixture. Basically the computer is designed to keep trying to advance ignition and reduce the injector duty cycle (lean the air-fuel mixture) until either a knock event occurs or the maximum amount of ignition advance and minimum amount of injector duty cycle is reached.

In the jeep, under normal circumstances, running 87 octane the computer probably has no problem reaching the maximum amount of ignition advance and the minimum injector duty cycle allowed. So running higher octane won't do anything.

When you tow a heavy trailer, the extra load will increase the chance of a knock event occuring (due to higher cylinder pressures especially at low RPM). If a knock event occurs the ignition timing will be retarded and the fuel mixture will be richened (injector duty cycle increased) reducing performance. Under these conditions using a higher octane fuel will prevent the knock, and will allow the PCM to operate with maximum ignition timing and minumum injector duty cycle.

So if you tow a heavy trailer and still use 87 octane the PCM may be required to run at less than it's maximum efficiency to prevent knock. Without a trailer you are unlikely to experience a knock event, so the PCM will probably be running at it's maximum efficiency even with 87 octane.

tjkj2002 · **Posted:** Fri Sep 07, 2007 3:29 pm

I use premimun all the time,then again I'm sitting at my GVWR(and have the JetII chip) and anything less then 90 octane makes my KJ knock.

Alak · **Posted:** Fri Sep 07, 2007 6:06 pm

The computer will not advance the timing with a higher octane fuel unless its under extreme load. There would be no performance gain in using a higher octane fuel on a stock Liberty. The computer will use the standard settings it sees with normal fuel on any octane. 89 octane is used as a precaution to towing because of the added weight and stress to the drivetrain. In hind sight, using 91 octane could potentially be harmfull in the long run as the engine is designed for lower octane fuel. Higher octane fuel also burns at a slower combustion rate.

The only way to see any gain on a factory computer with 91 octane is to take out the battery, step on the brakes and turn the light switch on and off a couple times.

Replace the battery, start your Jeep and drive it harder than you ever have before. When the computer is first reset, it will go through its range of programming fully to find the limit of that perameter. Reason for this is variances in elevation, etc. For example, it would advance the timing as much as possible as to not damage the engine to find when it would knock, but only under load.

The reason you have to reset the computer to do this is because once the computer programs itself, it only advances the timing milimeters of a degree at a time, instead of 2 or 3 degrees. It would take years to see any benefit from 91 octane.

I know because my mom did this for about 5 years (ran an 87 car on 91) before I learned about fuels. As far as Im concerned, Leaded fuel is the cats booty. Too bad it destroys everything.

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

You also need to consider altitude. At higher altitudes you can get away with lower octane because of the smaller amount of O2 for the same volume of air.

tjkj2002 wrote:

I use premimun all the time,then again I'm sitting at my GVWR(and have the JetII chip) and anything less then 90 octane makes my KJ knock.

You need to get the B&G flash. It's tuned for the premium too. It advances the timing and improves the shifts, but it also actually deletes the torque management which severely limits the power you can get to the ground. Mine made an extra 37 rwhp with the B&G than the stock PCM, and the stock PCM alone made 6 rwhp more than with the Jet I chip.

tjkj2002 · **Posted:** Sat Sep 08, 2007 11:10 am

Quote:

You also need to consider altitude. At higher altitudes you can get away with lower octane because of the smaller amount of O2 for the same volume of air.

That the total oppisite case with my KJ,I'm at 6200 feet,regular here is 85 octane,I'd never even think about putting that in my KJ,with midgrade(87 octane

)my KJ knocks,91 octane it runs good.Hitting the trails here in CO hitting 12,000ft sometimes my KJ runs way better with premuim anyway for the 4-low creep over the rocks.Now when back home in SD at 2200 feet I can get away with running regular(87 octane) but it runs like a rapped ape with the 93 octane premuim(15% ethenol).Go figure my KJ is a picky eater like I am :lol:

!

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

Yeah, but here at 1000 ft, 87 is regular, 89 is mid, and 93 is high. Mine really likes 93. Back when I was racing I was bumping it to around 100. I don't know how far the Jet II advances the timing, but it's probably a lot. That's why you need the higher octane.

tjkj2002 · **Posted:** Sat Sep 08, 2007 11:33 am

KY Liberty wrote:

Yeah, but here at 1000 ft, 87 is regular, 89 is mid, and 93 is high. Mine really likes 93. Back when I was racing I was bumping it to around 100. I don't know how far the Jet II advances the timing, but it's probably a lot. That's why you need the higher octane.

Yep,say's so it the destruction booklet that came with it.

Alak · **Posted:** Sat Sep 08, 2007 12:03 pm

I find fuel maker is a big deal too. For example:

My Miata and Porsche's ran fantastic on Shell 91 Octane V-Power

My KJ loves Huskey 87, but hates Shell

Mazda RX-7s that require low grade(octane) fuel love Esso, but everything else I own has no positive effect on esso.

Most Turbo cars feed off of Huskey 94 Octane around here.

I find that most cars if you constantly use a fuel on it, it will adjust to that kind of fuel. Im a big fan of Shell V-Power fuels, and most of my friend in high end cars use that fuel. I had an Acura TSX some time ago that ran on nothing but Shell V-power for its entire life. One time in hicks-ville somewhere, I put in some 'mystery' 91 octane and it really really didnt like that.

We're at about 2500 feet Above Sea Level I think. I dont remember.

sleeve84028 · **Posted:** Sat Sep 08, 2007 1:36 pm

Can you tow with a Porsche?

Couldn't resist

Higher octane for towing?

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