I Run 87 Octane but is this true!?

[BIG RED HEMI]

I always run 91 octane, but I have my truck tuned for 91. Diablo with Hemifever tune.

 

[Mr. Thinghuus]

Hi. New in forum. I've imported my 08 1500 mega cab over here to Denmark, Europe. Over here we only have as low as 92. - some places the lowest is 95. My truck drinks it all. - and a lot of it. ;-) and runs perfectly.
And over here it costs $ 1,7 per litre !!

 

[Dusty]

A few comments:

Going back to 2003 in Ram trucks I see no reference to the 5.7 Hemi being a Flex Fuel engine.

I checked my 2010 and 2014 Ram 1500 owners manuals and they both recommend 89 octane fuels in the 5.7 Hemi engines, as well as stating 87 can be used "with reduced performance and fuel economy." I seem to recall reading somewhere that the difference between 87 and 89 octane fuel in a Ram 5.7 is about 8-10 HP. Since spark control and engine basic timing is partially determined by the presence of a knock detection system, this makes sense.

Octane rating (RON+MON/2) and fuel ignition time are two separate, non-related parameters and are refinery manipulated. There is no direct correlation between octane rating (length of burn) and fuel ignition time (how quickly a fuel ignites or begins the burning process). In actual practice the fuel ignition times are generally the same across octane rated fuels. Fuel ignition time is a direct result of the fuel's volatility rating which is manipulated by the refiner and can vary across blends. Most refiners increase volatility of gasolines for winter use.

There was one post that seemed to imply (at least by the way is was written) that by using a higher octane fuel there would be an automatic increase in power. That is not the case in an engine designed for a lower octane rating unless the engine controls can adjust the timing to take advantage of the slower burning fuel.

Best regards,
Dusty

2014 Ram Big Horn 1500 Quad Cab 2WD, 5.7 Hemi, 8HP70, 3.92 LSD, factory dual exhaust, 20” wheels. Now at: 072701 miles.

 

[Factory]

You prob dont realize but your also making less power by running 87. There is a reason why RAM recomends 89 as a minimum. You can run 87 and your PCM will detune and reducing timing to keep the engine from Pinging. Sometimes its still audiable enough to hear (my neighbors 6.4 would ping when he ran 87). I can tell your a newb in this area so I wont go into specifics but Not just fueling by engine design has progressed very quickly in the last 20 years. Aluminum heads, fast burn kidney shaped chambers and lots of other goodies allows enough heat to be pulled from the chamber to allow higher compression and lower octane. More sensative knock sensors, Seqential fuel injection and not to mention now direct injection allows for alot more safety. Trucks tend to have lower compression due to heat generated (low speed high rpm like towing) puts alot more heat into the engine which is why they tend to have lower compression (detonation/pinging) and larger cooling systems.

I can guarantee that your engine will run better on 89 than in 87... enough for you to feel? maybe not but engine tune wise you'll prob make a few more HP and slightly better throttle response. With that being said... I run 87 bc I dont care for that little bit I'm losing. You'll be fine on 87 so just keep running it and saving the $0.30 per gallon as your not losing that much in MPG.

89 is to cover their ass for the oil blow by that builds up on the pistons & Heads ,making the need for 89 a suggestion instead of fixing the problem, bean counters saving $$$...

 

[01Ram2500]

Owners manual for my '14 recommends 89

So does mine.

 

[Casper]

You prob dont realize but your also making less power by running 87. There is a reason why RAM recomends 89 as a minimum. You can run 87 and your PCM will detune and reducing timing to keep the engine from Pinging. Sometimes its still audiable enough to hear (my neighbors 6.4 would ping when he ran 87). I can tell your a newb in this area so I wont go into specifics but Not just fueling by engine design has progressed very quickly in the last 20 years. Aluminum heads, fast burn kidney shaped chambers and lots of other goodies allows enough heat to be pulled from the chamber to allow higher compression and lower octane. More sensative knock sensors, Seqential fuel injection and not to mention now direct injection allows for alot more safety. Trucks tend to have lower compression due to heat generated (low speed high rpm like towing) puts alot more heat into the engine which is why they tend to have lower compression (detonation/pinging) and larger cooling systems.

I can guarantee that your engine will run better on 89 than in 87... enough for you to feel? maybe not but engine tune wise you'll prob make a few more HP and slightly better throttle response. With that being said... I run 87 bc I dont care for that little bit I'm losing. You'll be fine on 87 so just keep running it and saving the $0.30 per gallon as your not losing that much in MPG.

***
I think its reasonable to assume that by routing the PCV outlet back into the TB, RAM had to recommend 89 octane to avoid the PCM pulling power from pre-ignition caused by entrained crankcase blow by products. Hemi is no longer a super high compression engine after all.

 

[demort71]

Lots of good info being shared on here, but I will put in my two cents worth.

I have owned only three of the older 5.7L Hemi motors made between 04-08 2 Rams and a Charger. All of them called for 89 octane. I did on occasion run 87 octane and they seemed to run fine. However, I seldom ran more than a tank of 87 through them at a time. I did notice a difference on how they performed when I put in some 91 octane versus 89 or 87.

I live in the Midwest. I towed sometimes with my 05 Hemi Ram QC. It had the trailer tow package on it with 3.92 gears and 20" wheels. I used it to tow a 24' enclosed car trailer and a 1971 Challenger R/T long distance to car shows. I always ran 89 in it then. It did a great job except if I hit a long steep hill and then it worked a little harder, but it still kept speed with the O/D turned off. I was getting 10-11 mpg towing and as high as 19 mpg empty. It was a 2WD Ram. I have a 4WD Rumble Bee now with the tow package with 99K on it as a daily driver.

Risking any damage to the engine in my book isn't worth saving a few pennies at the pump. It costs a lot to rebuild an engine or buy a replacement. I guess if you can afford to own a truck that likes to burn gas, you can afford to buy the right fuel for it. Otherwise get a 4 banger car. LOL That's my philosophy. Evidently newer model trucks have had some changes to their ECU and they can automatically adjust the tune for the quality of fuel. My older Hemis didn't have that adjustment as far as I know, but they could burn 87 and I didn't hear pinging. Just saying...

 

[raginglaramie]

68powerwagon, refineries do not use toluene or ethanol to increase octane levels. Toluene isn’t used in gasoline. Toluene is paint thinner. Ethanol is used in gasoline cause it burns cleaner. Refineries add 2,2,4-Trimethylpentane aka isooctane to increase octane levels. I work in the oil and gas industry and understand the basic downstream process and my fiancé that works at the imperial oil refinery in Edmonton as a chemical lab tech explained to me what is used.

 

[Jetsfan122]

I find my truck runs much better on the 93 octane. And I only use Sunoco gas. It could be my imagination though, lol.

 

[SHOOT2KILL]

No one really knows if you are truly infact getting EXACTLY 89 octane when you pump...There are no stations with underground tanks of 100% 89 octane fuel...When you choose 89 on the pump, you are getting a MIX of 87 & 91 from both of those tanks...Who's to say the mixture is exactly 50/50 going in your truck...IMO...Cant trust the 89 to be actually the right octane, so I run 87 exclusively, because the 91 in my truck makes NO difference unless I'm towing at highway speeds, and even then the small gain in mpg is minimal and not worth the additional coin......