Jeep Wrangler Needs 91 Octane

[DeanD]

Have a 2020 Jeep Wrangler with 3.6 V6 engine and 6-speed manual transmission. Manual says it will run fine on 87 octane. Not quite true, it will run on 87 octane and not ping but won't live up to it's power potential. I was told by another Wrangler owner that 91 octane premium works much better so I tried it. Couldn't believe the improvement in power, start off, acceleration, pulling up hills on the open road. On 87 octane I had to rev the engine pretty good to take off in 1st gear or the engine would stumble and stall. Now it will take off in 2d gear better with 91 octane than it did in 1st with regular fuel, in 1st I can just let the clutch out without increasing the rpm and it just takes off. Traveling southbound on the 215 in the area of Lake Mead there is a strong uphill grade, on regular fuel I had to downshift to 5th then down to 4th to pull the grade and I dropped a lot of speed. With premium fuel I don't have to leave 6th gear and it holds 70-75 mph. The acceleration and throttle response is so much better on premium, like driving a different vehicle. Now I know if an engine in designed for regular fuel you are just wasting money to buy premium and you get nothing. The rub here is it is difficult to say the 3.6 V6 engine is "designed to run on regular", well it does but not very damn good. It has 11.3 : 1 compression ratio! That is up there with the old muscle cars and that is incompatible with 87 octane. Period!

How does an engine with 11.3:1 compression ratio run "ok" but (poop)ty on 87 octane? Easy, the computerized engine management system just retards the ignition timing and manipulates the variable valve timing to lower cylinder pressure to eliminate pre-ignition and pinging. 91 octane fuel just makes a whole different engine out of it.

I don't know if Fiat was involved in the design but I do know that European gasoline has a AKI (anti-knock index) of 90 vs. 87 in the USA so the engine would run much better on the European gasoline with such a high compression ratio.

 

[Gullwing]

People use 87 octane????????

 

[MAC702]

People use gasoline?

 

[EXCAL]

Yep it's Fiat's fault. It's the Euro mentality. They run little baby 1-2 liter engines with 11+:1 compression - gas is very expensive so people want little engines but still demand some level of performance. Now they are trying the same tricks here. In the past compression was an enemy of emissions but now as you point out they can negate the effects with cam timing. I suspect there is a very narrow band that this engine passes emission in and as it ages that will become more difficult - just as it was when Chrysler was using GM v6s with Chrysler designed emissions equipment on them.

For 2016, FCA released an updated version of the 3.6 L engine for the Jeep Grand Cherokee and Dodge Durango. This engine now featured two-stage variable valve lift (VVL), a cooled EGR, a new intake manifold, new fuel injectors, and new ignition coils. It also features upgrades to the variable valve timing (VVT) system, an increased compression ratio (11.3:1), lower internal friction and lower weight. These improvements help to increase power as well as efficiency.[8] The new version, however, has lost its flex-fuel capability.

 

[lvjunk]

Yep it's Fiat's fault. It's the Euro mentality. They run little baby 1-2 liter engines with 11+:1 compression - gas is very expensive so people want little engines but still demand some level of performance. Now they are trying the same tricks here. In the past compression was an enemy of emissions but now as you point out they can negate the effects with cam timing. I suspect there is a very narrow band that this engine passes emission in and as it ages that will become more difficult - just as it was when Chrysler was using GM v6s with Chrysler designed emissions equipment on them.

For 2016, FCA released an updated version of the 3.6 L engine for the Jeep Grand Cherokee and Dodge Durango. This engine now featured two-stage variable valve lift (VVL), a cooled EGR, a new intake manifold, new fuel injectors, and new ignition coils. It also features upgrades to the variable valve timing (VVT) system, an increased compression ratio (11.3:1), lower internal friction and lower weight. These improvements help to increase power as well as efficiency.[8] The new version, however, has lost its flex-fuel capability.

My 2015 JGC has flex fuel capability (not that I’ve found flex fuel to even try in it) and runs great on 87. I’ve not noticed any significant difference when running 91. My third and favorite jeep so far (after two previous wranglers).

 

[DeanD]

lvjunk, your 2015 has 10.2 compression so typically there is nothing to be gained by premium fuel. As EXCAL said above the compression went to 11.3 in 2016.

 

[DeanD]

Jeep says in the owner's manual that the 2.0L 4-cylinder that it is designed to provide satisfactory performance with 87 octane fuel. It goes on to say: "The use of 91 or higher octane "premium" gasoline will allow these engines to operate to optimal performance." For some reason the description of the V6 omits that statement. Possibly because the 4-cyl was just introduced in 2018 and the description of the new engine was added to the owner's manual whereas the V6 has been out for several years and the original 10.2 compression ratio would get no improvement with 91 octane so the statement would not have been applicable. Just thinking that maybe they didn't edit the owner's manual when they bumped up the compression. Just a guess.

 

[Good To Go]

My wife would like to buy a new jeep wrangler. When it gets cooler she will do some test drives. Wonder what the dealer puts in the tank?

 

[sai]

Higher octane slows the burn/combustion. All it has to do is pull timing to run lower octane. Thats what your feeling on the low octane gas. N/A cars deal with this a lot better but forced induction is much finicky when it come to gas quality.

 

[Tophog]

People worry about emissions testing?

 

[EXCAL]

My wife would like to buy a new jeep wrangler. When it gets cooler she will do some test drives. Wonder what the dealer puts in the tank?

Probably nothing. They usually come from the factory with 5 gallons. If the dealer does a fillup after the sale I can assure you they use the cheap stuff.

 

[EXCAL]

Higher octane slows the burn/combustion. All it has to do is pull timing to run lower octane. Thats what your feeling on the low octane gas. N/A cars deal with this a lot better but forced induction is much finicky when it come to gas quality.

Forced induction is basically just raising the compression ratio. It stuffs more air/fuel into the cylinder then compresses it into the same space of a NA engine. These new engines with very high compression also change the valve timing to limit the amount of air getting into the cylinder making the effective compression ratio lower and chance of detonation. Timing adjustment is basically just handled by a knock sensor. When it detects pinging it retards the timing.

 

[DeanD]

I have to say I really like my Wrangler. I bought the basic 2020 Wrangler Sport 2-door and was more interested in the mechanical options: tow package, HD alternator and battery, limited slip differential, V6, 6-spd manual. I have manual door locks, crank up windows, do have the hardtop, AC of course, and XM radio. They all come standard with tilt/tele steering wheel, cruise control, steering wheel controls, Bluetooth, backup camera, 5" touch screen. I find the quality superb, assembly and finish flawless, paint is like glass, the entire chassis and suspension and steering components are painted satin black. I have a Mercedes CLS and seldom drive it since I bought the Jeep. I paid about $30.2k for it before sales tax. Current Kelly Blue Book is about $1,800 over what I paid new. They hold value like nothing out there. Wouldn't even think of buying a used one. Bought mine at Jeeps Only on Sahara but they are as shady and incompetent as any of the others. I paid cash and they sent my title to some credit union with a lien on it. Took a couple of months to get a title. Unbelievable. Tried calling for two days last week to schedule an oil change but they never answered the phone in service and didn't return my voicemail Finally drove down and did the express oil change. Anyone connected with car sales or real estate pretty much sucks.

 

[arashi]

Interesting. I have a 2016 wrangler and have only run 87 octane in it. I'll have to try some 91 out.

https://www.cjponyparts.com/resources/pentastar-v6-specs

2016 PENTASTAR CHANGES
The Pentastar has received one revision during its lifetime, in 2016. The refresh resulted in improved engine reliability. Horsepower and torque output increased, while fuel consumption and emissions output decreased.

Two-Stage Variable Lift
One of the big ways these adjustments were made was through the implementation of two-stage variable lift. This allows for a more exact amount of fuel to be used at the appropriate RPM. Along with this, the Pentastar V6’s variable valve timing (VVT) was recalibrated.

Increased Compression Ratio
The compression ratio was raised from 10.2:1 to 11.3:1. This was made possible by a few knock reduction measures taken in the design of the engine. One of these was the liquid-cooled exhaust gas recirculation system.

Various Parts Improvement
There are a variety of other changes like a new plastic intake manifold runner, new valve springs, low tension piston rings, and eight-hole fuel injectors.

 

[sai]

Forced induction is basically just raising the compression ratio. It stuffs more air/fuel into the cylinder then compresses it into the same space of a NA engine. These new engines with very high compression also change the valve timing to limit the amount of air getting into the cylinder making the effective compression ratio lower and chance of detonation. Timing adjustment is basically just handled by a knock sensor. When it detects pinging it retards the timing.

Yea, I don't like how manufacturers use knock sensors. All my turbo builds used O2 sensors and exhaust temp sensors too monitor how rich or lean my motor ran. I also had a tune for each octane 91, 100 and c16.

 

[Dr. Marneaus]

So what are you seeing for fuel economy on the 87 vs the 91?

I have a 2019 with a 3.6 and I have read that moving up in grade basically washes out the cost given the improved fuel economy. Not to mention it’ll run and perform way better overall. So yes 91 costs more but getting another 10% in fuel economy makes up for it.

Ours is an auto because wife.

 

[Jeepin]

That's the first I've seen someone say that a stock 3.6 needs premium. Usually the 3.6 guys use the premium fuel excuse as a reason they'd never consider a 2.0, and that's wrong. They Run fine on regular.

Interesting. I have a 2016 wrangler and have only run 87 octane in it. I'll have to try some 91 out.

https://www.cjponyparts.com/resources/pentastar-v6-specs

2016 PENTASTAR CHANGES
The Pentastar has received one revision during its lifetime, in 2016. The refresh resulted in improved engine reliability. Horsepower and torque output increased, while fuel consumption and emissions output decreased.

Two-Stage Variable Lift
One of the big ways these adjustments were made was through the implementation of two-stage variable lift. This allows for a more exact amount of fuel to be used at the appropriate RPM. Along with this, the Pentastar V6’s variable valve timing (VVT) was recalibrated.

Increased Compression Ratio
The compression ratio was raised from 10.2:1 to 11.3:1. This was made possible by a few knock reduction measures taken in the design of the engine. One of these was the liquid-cooled exhaust gas recirculation system.

Various Parts Improvement
There are a variety of other changes like a new plastic intake manifold runner, new valve springs, low tension piston rings, and eight-hole fuel injectors.

They didn't put the revised engine in the JK. They Started using it in the JL.