Man I envy you!!!! I just made a 20 mile trip across town and when I was doing 80, my tach was pushing 2600 rpm's!! Then again, that's the drawback of having 3:92 gear ratios.

 

I just wanted to add this bit to this discussion about octane requirements: I have bolded the fuel requirement for my veh:

ENGINE: 5.9-LITER MAGNUM®, OHV SMPI V-8
Availability Optional — all
Type and Description 8-cylinder, 90° V-type, liquid-cooled
Displacement 360 cu. in. (5895 cu. cm)
Bore x Stroke 4.00 x 3.58 (101.6 x 90.9)
Valve System OHV, 16 valves, roller followers, hydraulic lifters
Fuel Injection Sequential multi-portpoint electronic
Construction Cast-iron block and heads
(a) With EPA Tier 1 exhaust emission controls.
(b) With California Ultra Low Emission Vehicle (ULEV) exhaust emission
controls.
(c) Meets Ultra Low Emission Vehicle (ULEV) requirements in California:
Meets EPA Tier 1 requirements in all other states.
Compression Ratio 8.9:1
Power (SAE net) 245 bhp (183 kW) @ 4000 rpm (42.4 bhp/L)
Torque 335 lb.-ft. (454 N•m) @ 3200 rpm
Max. Engine Speed 5250 rpm
Fuel Requirement Unleaded regular, 87 octane (R+M)/2
Oil Capacity 5 qt. (4.7L)
Coolant Capacity 14.3 qt. (13.6L)
Emission Controls Mini-catalyst(a), three-way catalytic converters, heated
oxygen sensors, engine modifications(b)
Estimated EPA Fuel Economy mpg (City/Hwy) 12/17

 

The higher the compression ratio of the engine the greater the need for more octane in the fuel to slow down the combustion rate. If you are burning high octane fuel in an engine with standard compression ratio of around 8:1 you are wasting your money and hurting performance. As long as the engine does not ping you are fine using a lower octane fuel. All octane does is slow down the burn so that the fuel does not ingite to early so that you can get the most out of a high compression engine. So many misunderstand what octane really is and what it is meant to do. They think that the higher octane fuel automatically means 'more power' - wrong. So don't waste your money and maybe even hurt your performance by using the higher octane fuel when you don't require it.

 

True and false.

If you run higher octane = slower burn which is a better burn causing less fuel needed to create the same power. Thus with less emissions less fuel is needed creating an increase in mileage. Slight but yet an increase.

For instance, When I tow I use 91 (highest here at the elevation) Chevron. This gives me more power because of a slower cleaner burn = higher tow mileage and less motor fatigue needed. For normal usage, use what the owners manual specifies unless it pings ^ as indicated by Factory. ^

Also be aware that at higher elevations the same octane reading will be less. At sea level regular fuel is 87 octane and at 3500 elevation that same fuel is only 85 octane but you can still use it unless there is ping. (pre ignition)

The factory sets settings to 87 octane which is regular fuel at sea level. The Fed's set that requirement. If the motor is anything other than it is because of compression ratio and they need to label it and also include it in the owners manual.

 

One more thing to add. You can always use cooler or hotter plugs and create the same effect. Some owners use Autolites 3923's which are a step cooler and not of OEM (Champion brand) plugs in the 5.2L and 5.9L engines.

I don't like them and discourage their use. Platinum plugs don't work in these motors! But this causes a interruption to the motor and the PCM (tricks the PCM) to run a retarded timing to stop the ping. I prefer to use the right fuel and right octane.

 

Ok so I have a 2001 Durango R/T and let me tell you it DOES matter what fuel u put in, I put the cheaper gas in a few times and it does run like crap!!

 

Storm, you know this is a 6+ year old thread, right? But since you triggered it... define 'crap'.

I have a Hypertec Power Programmer in mine set at the '93 octane' position. It usually pings a bit on regular, so I've been using midgrade for years with no problems. I even added a 180° stat and still no probs with mid-grade.