Your engine will not get Addicted to a fuel - it is a mechanical piece of metal, it has no emotion and no abilty to get addicted to anything...

An octane rating is a calculation that determines a point of ignition, a higher rating means that it will resist premature ignition (typically referred to as a knock or ping). An engine that is tuned for a certain detonation or ignition point should have a fuel that is matched for the set point. Many factors can change this point as well, such as altitude or temperature. Typically in the colder months or when pulling lighter loads the benefits of using the premium (higher octane) fuels won't even be realized.

In this case, obviously the 2001 model was tuned to ignite at a point above higher than the resistance point of both mid-grade and regular unleaded fuels... I am sure that the changes to the ignition system, or the settings on the ignition system, would be minimal in order to have detonation occur at a lesser temperature, allowing the use of all grades (which apparently Dodge did on differing model years)

 

Ok, I am not an idiot, I was just making a statement and I wish I had the old owners manual. It stated something like if you continue to use premium fuel when you may have to keep using it or when you go back to regular you will experience pinging or knocking....maybe it was my 98 Dakota...anyway nothing to argue about here, it looks like they finally fixed something.

 

I did not mean that to be confrontational or anything, and I also did not mean to imply that you were not intelligent... I guess it did come across that way, my apologies...

 

No problem....all is well. No matter what, I bet there is not a Durango owner out there getting "good" gas mileage. I bet we can all agree on that, and if you bought one hoping to (as it has been stated before) you made a big mistake. I hope all of us Durango drivers can continue to drive our beloved vehicles due to gasoline prices.

 

I wonder if the premium fuel it only applies to the years 2000 to 2001 or 2002 because of the recalibrated computers to give you that extra negligible horsepower/torque? I think for those of you that do not require the premium fuel, it could be that Dodge just stuck in a standard 5.9 without the re-calibrated computer to get you that extra 5 horses and 5-10 lbs of torque???

At this stage with fuel prices going up, I would like to deprogram my computer to not use premium unlead as the tiny hp/torque increase does not any difference in performance.

 

Man , you do tach a little high, I tach at 2000 rpm's at 80 mph. I will post pic soon.

I think some of the variences we see are due to different tire sizes.

 

Digitoxin,

I posted a little earilier on this thread about tire sizes affecting the Tach to speedo relationship and it does not change it at all. The tire size will only change the relationship between the speedo and the actual speed you are travelling. The relationship between the Tach and the speedo is govened by the transmission and the gear ratio of the axles. Changing to a taller tire for example, you tach and speedo will still remain the same, but your actual speed will be increased. The same applies to going to a smaller tire. Tach and speedo remains the same, but your actual speed will be decreased. I know from experience as I got ticketed and was able to talk my way out of it in court when I showed the judge of my very recent tire change receipts. I was doing 65 on a 60 limit and got ticketed going 71 on a 60. This was on my Toyota 4WD. I changed out from a standard truck tires to 31 inch offroad tires. My speed and tach relationship remained the same. My speedo was set on 65 but I was actually doing 71 according to the trooper's radar.

My best guess to these variances is because later models of the Durango R/T's may have a different transmission or possibly a taller overdrive gear. All Durango R/T's defaults with 3.92 axles so this variance must be within the transmission gearing itself.

This also explains the variances in gas mileage for differnt R/T owners as well. So far, I was able to increase my gas mileage to 12-13 city and 14-15 on the highway by using K&N stock filter replacement and going to the Champion double platinum spark plugs and keeping a very light foot and keeping my throttle body clean every 3 months by spraying B12 carb cleaner to remove some of the very light gunk build up on the throttle plates, etc.

I would bet my MPG may be 1-2 mpg's better if I had the taller OD gear or whatever to get my tach down to below 2k when travelling at 70 mph which is my cruising highway speed at current Texas highway interstate speed limits. Now Texas as moved the speed limit 80 mph on some interstate roads starting 01/01/2006. I don't think I want to wind up my Durango that fast as my engine speed may be hovering around 2500-2600 rpms much less sucking away any advantage I get on mpg's! haha

 

If you took it to the extreme, and changed the tire size to, say, a little red wagon wheel, the tac and speedo
would have to be different. A average tire size change usually has a 3, to 6 mile an hour change. The change
in the tac to speedo may be less.

To determine your vehicle's engine rpm with its present tires, simply measure the diameter with a tape measure. If the tires have a convex tread surface, be sure to allow for it when you measure them.

RPM x Tire Diameter X 336 = MPH
Drive Ratio x 336


Engine RPM at 60 MPH

Ratio 31"Tire 32"Tire 33"Tire 34"Tire 35"Tire 36" Tire
3.08 2000 1950 1875 1825 1775 1725
3.23 2100 2025 1975 1900 1850 1800
3.31 2150 2075 2025 1975 1900 1850
3.42 2200 2150 2100 2025 1950 1900
3.54 2300 2225 2175 2050 2000 1975
3.78 2425 2375 2300 2200 2150 2100
3.90 2550 2450 2375 2300 2250 2175
4.10 2650 2575 2500 2425 2350 2300
4.27 2775 2700 2600 2525 2450 2400
4.56 2950 2875 2775 2700 2625 2550
4.88 3175 3075 2975 2900 2800 2750
5.12 3325 3225 3125 3050 2950 2875
5.38 3500 3400 3300 3200 3100 3025

 

You are correct as you are basing this fomula on true actual MPH. Not what the MPH is reading from the speedo. I am just stating the relationship of the speedo and tach will always remain static as nothing has been changed on the tranny itself. Example, if you were staring at the speedo at 60 MPH, the tach will say 2000 rpm's. Changing tire sizes will not change this relationship. Changing tire sizes will change the relationship of the actual MPH and the MPH reading on the speedo. This is why owners must recalibrate their speedos if they change tire sizes big or small enough to make a major impact on the accurate MPH reading on the speedo.

So on my Toyota, after I have replaced my regular tires with 31 inchers and barely talking my way out of a ticket, I had to go to a speed shop and have my speedo recalibrated to adjust for the 31 inch tires. After the speedo is recalibrated, this changed the relationship of the tach to the speedo and the new speedo reading now shows I am running at lower rpm's using the bigger tires. This scenario fits your formula now that my speedo reading is showing accurate MPH.

If you have doubts, try it yourself, go change out your tires on your D. Don't calculate what your true MPH would be using your fomula. Most users that changes their tire sizes aren't aware that their speedo is not accurate any longer. This is why they get pulled over for going too fast and argue with the cops that they weren't speeding. You'll see the speed and tach relationship remains the same. Only your true MPH will change.

 

Here is my speed to tach readings. REAR END : option code - OMD=3.55 gear ratio
option code - OSA= anti-slip