DodgeTalk Forum banner

What octane rating do you use?

  • 87

    Votes: 484 43.5%
  • 89

    Votes: 474 42.6%
  • 90+

    Votes: 109 9.8%
  • My truck runs on cheese

    Votes: 45 4.0%
Status
Not open for further replies.

Do you use the recommended 89 octane?

117K views 385 replies 192 participants last post by  WalterG 
#1 ·
Please post any reports of whether you notice a difference in mileage, engine idle, etc....
 
#2 ·
I would not run your truck on cheese. It will make it constipated. :D
 
#4 ·
I've always ran the 89 in my 04 Hemi.
 
#5 ·
I use 89. The owner's manual says that the 390hp and 407ft/lb ratings were done with 87 octane though which is awesome to know.
 
#9 ·
I have a superchips on my 02 Ram and I have to use Premium 92 or better. I haven't noticed a major change in my gas budgeting with using the more expensive fuel. if I had an 09 I would use 89 or better
 
#15 ·
I always use premium... its usually a 20c martkup and i dont mind that.. so on a 30 gallon tank thats only $6 more...

and since im spending $60+ anyway.. whats the extra $6... I felt the difference in my old supercrew and told myself that even if the $6 just barely increases the power, gets me a just a few mpg more or helps things run a lil cleaner in my $45,000 truck.. then so be it
 
#43 ·
Misconception, Octane ratings are simply longer chain carbon links, and are the fuel's ability to resist pre-ignition. In fact running higher oct fuel than the engine can compensate for through timing advance can mean less MPG, and the fuel not burning completely in the combustion process than the lower/intended oct rating. This means a dirty burn and fowled spark plugs. You can see this when you change your spark plugs, as how the plugs look. Since the 09ram book says 87-89 for hemi's, the truck's not going to be able to advance much higher to compensate for higher than 89 oct fuel. Now if you run an ecu flash, and a tune specifically for 91-94, then yeah, go for it, you'll get more power. Oct ratings also have little to no impact on fuel mileage (other than noted above) as the fuel still contains the same amount of stored energy, you will however see MPG variances based on the amount of detergent in the fuel (cleaners), Oxygen (esp in winterized fuel), and Ethanol %. So higher grade fuels will not net more mpg's, as your vehicle may not be able to take advantage, and may even take a performance deficit.

Marketing is to blame for these misconceptions, terms even in the grades (reg, mid-grade, premium) seem to indicate that premium is better than regular, while the truth in that answer is that it depends on what the motor is tuned for, and what the ecu can compensate for (some cars can compensate for a lot more than others). It also takes time and mileage for the ECU to learn, so constantly switching back and forth between 87 and 89 can also be bad.

There is also a difference in brand of fuel. While most gas comes from the same place, top tier stations usually use the better 3/4's of a barrel for their gasoline, where the lower end stations get cheaper stuff settled to the bottom, they will also use less, and less developed detergents which means less carbon cleaning power.



tl;dr notes:
Run whats recommended, unless you have tuned the ECU to higher oct rated fuels. ;)
 
#20 ·
I run 87 the only thing high octain does is knock additive.I worked at a Refinery,and they had a room no one was allowed in. Off site.Me being a tech could go anyware.One day I decided to sneek in this off limit room,I will just play dumb,and they never queston a guy with a tool pouch. Their were about 100 350cuin engines,with 3 guy in white lab coats.Of course one came to greet me.I said wow what's this.He said its the knock room,this is how we tell if it regular or premium gas.Yes no big difference,if it knocks regular.That was good enough for me.
 
#31 ·
im sorry but does anyone else read this and have a hard time believing this? i mean, if it was an "off limits" room, why would they give access to a handyman to just barge in without authorization? also, if there was an off limits room, surely SOMEONE would know what went on in there. if it was soooo sectretive i dont think you would just be able to walk in and be greeted my someone. there would be cameras and locks on doors. and y would they want to keep that stuff under wraps anyways. they are just figuring out what gas they got. also, are you telling me that they tell what type of gas they just made by tossing it in a few chevy engines? you mean they cant just use an octane tester ? would that be too easy? sorry but its tooo far fetched for me to believe all this.
 
#21 ·
I can't prove this, but I could swear I've noticed a slight DECREASE in power on 93 octane. That is not unheard of-it is entirely possible to lose power with more octane than you need. This has been seen on dynos occasionally. It does not hurt the engine, but can reduce power.

I still question whether I was imagining this or not, as a 10 and a half to one engine doesn't seem like it ought to need so little octane that 93 octane would cause power loss.

Like I said, I won't swear that I'm right on this, but my truck did seem a tad slower on straight pump premium vs lower octane stuff, and I was expecting it to be quicker.
 
#22 ·
The Dodge Q/A said here that higher octane will improve power output, but they didn't say how much. I'm guessing the HP difference between 87 and 93 is less then 4-5HP with the stock programming. The knock sensors on these engines are ridiculously sensitive, and they are run with fairly retarded ignition to start with.

I'm guessing its more like a placebo effect. You were mentally expecting a fairly good difference in speed/power, and when that didn't happen, it felt like the truck was slower.
 
#23 ·
I'm using 91 now but with the high preformance tune.
 
#24 ·
You're right that these trucks don't run much timing. I have a scan tool that I have hooked to mine while driving, and advance hovers around 18-20 degrees under light throttle cruise. If any of you have watched the advance numbers for older design engines, you're probably aware that light throttle cruise is usually MUCH MUCH higher, something like in the 40's of degrees. Generally speaking, the less efficient the combustion chamber design, the more advance it needs and will tolerate. Case in point-an older smallblock chevy (or any other motor) with open chamber heads will often like a total advance of around 36-38 degrees, with more under light throttle cruise.

Better chamber designs that promote a faster burn neither need or can tolerate that much advance. They don't need it because the time between the spark and when most of the burn is completed is shorter than older designs, so they don't have to light it off way before the piston gets to TDC. They don't want it because if you initiate the burn way ahead of TDC like older motors, the fast burn will have cylinder pressure rising WAY ahead of when it will make optimal power. In fact, if you ran 30-some odd degrees of advance in a modern design that likes less timing, I suspect it would either not run at all or would knock itself to death quickly because peak cylinder pressure would probably be occuring before TDC.

When I filled my tank up with 93 octane, I expected to see the advance figures rise somewhat, at least a couple of degrees. Instead I saw no change at all. It could be that under the temperature conditions I was running it, 87 octane was enough for all the advance that the stock programming allows. If that is the case, running much more octane would in fact reduce power by delaying the burn a little past the optimal point. It's just hard for me to think that a stock motor running a stock high temp thermostat with 10.5:1 compression would not be knocking at all on 87 octane with ambient temps in the high 70's.
 
#25 ·
I run 89 in my 04 Durango around town.

However, when I'm driving in the interstate (I95 heading south for 300 plus miles, I run 91 since I'm crusing around 75 mph. I believe if you driving at higher speeds, a higher octain will help with performance, especially for the Hemi. Just my 2 cents. I even put higher octain in my 96 Ram when I'm driving on the interstate and the old Ram enjoys that too!
 
#26 ·
With my 2003 Durango, I have superchips set at the 91 octane setting, and I run 87 octane. I have 1 step colder plugs. No pinging or knocking at all. But I am at a higher elevation, and we don't need as high of octane. Hell, it was only about 6 months ago that the lowest octane was 85. It went 85 - 87 - 89. Now they have changed over to a higher octane. Now it is 87 - 89 - 91. I have tired running 91, and I didn't notice 1 lick of difference at all. So I go back to 87 because it works just as good and is 20 cents cheaper per gallon.
 
#27 ·
the owner book says to us 89 so i'm using 89
 
#30 ·
I use the 87 just fine and I did notice especially on my 05 that the 89 which I believe is boosted to this number most of the time with ethanol got about 2 mpg less.
 
#32 ·
That is a disgustingly in inefficient way of checking fuel octane - and inaccurate, Plus, 350s under constant knocking would blow up in short order.

Actual octane testing engines are quite complicated, and have a nearly infinitely variable compression ratio, from 6:1 to 20:1 or more for testing diesel as well. Along with highly scientific equipment attached to it to test for even the slightest pre-detonation. Engines can have mild pre detonation as well without physically knocking, you wouldn't be able to tell jack going by knocking in a room with 100 350s running full throttle.
 
Status
Not open for further replies.
You have insufficient privileges to reply here.
Top