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-   -   MPG and Octane conclusion (http://www.ramforumz.com/showthread.php?t=91887)

belle 09-13-2011 06:27 PM

MPG and Octane conclusion
 
After 10,000 miles of experimenting with different octanes, I have come to this, my personal, conclusion. My 2011 Laramie Crew Cab runs better, sounds better, and gets better mpg primarily using 87 octane and occasionally using a tank of 89. I use the 89 about every fourth fill just to be clean up any problems, if any, with the 87. My biggest concern is with ETHANOL !!!

SS4Luck 09-13-2011 07:12 PM

Thats funny, I only have 2300 or so miles, but Ive gotten best on 93, seems to stay in eco mode longer and pulls the little hills in eco as opposed to running a lower grade.

What mods do you have on your truck?

FireWire 09-13-2011 07:34 PM

There has been a lot of threads on this.
Some swear that 89 is better and some say no difference from 87.
I am a bit cheap and have only ran 87 since I got my truck.
Now gas prices have gone down and 89 is the price 87 was last week.
I guess I'll finally try a tank of 89 and decide for myself.

GTyankee 09-13-2011 08:21 PM

I usually use the 89, but when prices climb, i may use some 87 between tanks of 89, so it may be more like 88 octane.
Now when i cross into Arizona, i only use 89, prices are 20 to 30 cents cheaper a gallon

The reason that they suggest using 89 octane is because of the Compression ratio
Displacement 5.7L (345ci) Compression Ratio 9.6:1
Bore 3.92 in. (99.5mm) Torque 375 @ 4400 RPM
Stroke 3.58 in. (90.9mm) Horsepower 345 @ 5600 RPM
Fuel Type Gasoline 87 Octane Net Weight 92.9 kg (205 lbs.)
Fuel Induction Sequential Multi‐port Fuel Valve gear OHV MDS 2v/cyl

The general rule is
87 octane up to a compression of 9 to 1
89 octane up to a compression of 10 to 1
91 octane up to a compression of 11 to 1

103 can be used up to 16 to 1


worthless stuff
there are many other variables & 2 different compression types, 1 is DYNAMIC, which i think is the one that engine manufactures use

Compression Ration =
Cylinder vol. + clearance vol. + piston Comp. vol. + gasket vol. + chamber vol. divided by Clearance vol. + piston vol. + gasket vol. + chamber vol.

Read more: http://www.carcraft.com/techarticles...#ixzz1XshuZNpp

erm 09-13-2011 08:51 PM

Well, what I've noticed in tuning several HEMI's using a Predator or Trinity is that they are all different. One likes a higher octane with a middle of the road air/fuel ratio, another one likes mid-grade with a rich mix, some like higher octane with a rich mix, yadda yadda yadda.

I'm not surprised by this finding by belle. I did the same thing with mine and 92 octane works best for me.

Thanks for the info, belle! Every little bit helps.

garner 09-14-2011 06:34 AM

Quote:

Originally Posted by GTyankee (Post 612852)
I usually use the 89, but when prices climb, i may use some 87 between tanks of 89, so it may be more like 88 octane.
Now when i cross into Arizona, i only use 89, prices are 20 to 30 cents cheaper a gallon

The reason that they suggest using 89 octane is because of the Compression ratio
Displacement 5.7L (345ci) Compression Ratio 9.6:1
Bore 3.92 in. (99.5mm) Torque 375 @ 4400 RPM
Stroke 3.58 in. (90.9mm) Horsepower 345 @ 5600 RPM
Fuel Type Gasoline 87 Octane Net Weight 92.9 kg (205 lbs.)
Fuel Induction Sequential Multi‐port Fuel Valve gear OHV MDS 2v/cyl

The general rule is
87 octane up to a compression of 9 to 1
89 octane up to a compression of 10 to 1
91 octane up to a compression of 11 to 1

103 can be used up to 16 to 1


worthless stuff
there are many other variables & 2 different compression types, 1 is DYNAMIC, which i think is the one that engine manufactures use

Compression Ration =
Cylinder vol. + clearance vol. + piston Comp. vol. + gasket vol. + chamber vol. divided by Clearance vol. + piston vol. + gasket vol. + chamber vol.

Read more: http://www.carcraft.com/techarticles...#ixzz1XshuZNpp

Compression ratio on the 4th gens is 10.5:1

belle 09-14-2011 07:45 AM

I've never used 93, but I'll try it next tank. I heard that 93 octane doesn't contain ethanol. Is that true?

doug713 09-14-2011 10:32 AM

In the warmer months there really is little to no ethanol in the gas, I beleive they mainly use it in the gas during the colder months,, at least thats what I've found around here....

snrusnak 09-14-2011 10:37 AM

Ugh all this ethanol talk....they might as well just use 10% water instead, it'd save them money....

From what I've seen most have the best luck with 89 on their hemis.

garner 09-14-2011 01:14 PM

Quote:

Originally Posted by belle (Post 613122)
I've never used 93, but I'll try it next tank. I heard that 93 octane doesn't contain ethanol. Is that true?

It depends on the gas station. I've seen some where they have no ethanol listed by 93 but I've seen others where they have the little ethanol sticker by all octanes


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