5.7L V8 Magnum Needs 89 Octane?

[PTW105]

Hello. I'm looking at a '06 V8 AWD Magnum and have read everywhere that the V8's need 89 octane. With 89 octane being right at $3.99 a gallon, and $3.79 for regular 85 octane is it really necessary to have 89 octane? What will it affect if I put in 85 octane?

Thanks!

[jkelly16]

Not sure but I don't think you can go below 87. Running less than the recommended octane will cause spark knock which will cause the pcm to pull timing and it doing that constantly is not good.

[NOTPAID4]

89 Octane is highly recommended for these 5.7L Hemis. I would NOT run anything less. You get worse gas mileage with 87 Octane and could damage the car. My 05 R/T (my everyday driver) averages over 18MPG local; no freeway driving. Can't beat that for a V8! I have even hit over 20 on a few tankfuls. (Keeping the plugs changed really helps too!)

[horsedragon]

We have had our 2005 Magnum since new. The engine is stock. We have always run 87 octane in it. I have never heard it knock, even under heavy acceleration or towing and it consistantly gets 24 on the highway and 18 around town. I put platinum plugs in it and accell coil packs on it at 110K.

[Hendogg]

Originally Posted by horsedragon

We have had our 2005 Magnum since new. The engine is stock. We have always run 87 octane in it. I have never heard it knock, even under heavy acceleration or towing and it consistantly gets 24 on the highway and 18 around town. I put platinum plugs in it and accell coil packs on it at 110K.

You are lucky then.. My 05 r/t gets around 14/16 when we have ran 87 in it and gets around 18/20 with 91. And that is a 40/60% city/free way driving. Now my 06 dodge ram 2500 4 door 4x4 gets 6-8 with 87 and 12/14 with 91..


But the 5.7 hemi is built to run on 89 or better and is programmed for it as well because of the slower burn if you are going to run 87 or lower in it you really need to by a programmer where you can change the computer to be able to run right on 87 or lower octane fuel because of the faster burn time.. 87 burns faster than 89 is why you don't get the mpg like you will with the 89 where 91 burns even slower than the 89..

[FloridaRT]

I use a tuner (Superchips) and run the 91 octane tune, in my area we don't have 91 octane so I buy 93 octane.

Bob

[oldyellr]

Interesting thread. I've owned a few cars that called for 89 octane but I ran 87 (regular gas) with no ill effects whatsoever. I just wasn't anal enough to do long term comparisons between 87 and 89 or 91 to see if 89 actually saved me money. For sure, running 89 if that's recommended will get you better performance at the drag strip.

Which brings me to my issue. I just bought a 2005 SXT, 3.5 liter. Before I even knew that 89 octane was recommended for the Hemi and 3.5 I filled up with 87 and noticed no knocking (which is as it should be because the computer will retard the ignition if it senses knocking). Also, my son just recently bought a 2008 Aspen Limited with the Hemi and went on a road trip hauling a 34' travel trailer, also just using 87 octane gas most of the time. Also no distress. For the Aspen the owner's manual states,

The 5.7L engine is designed to meet all
emissions regulations and provide satisfactory
fuel economy and performance when
using high quality unleaded gasoline having
an octane range of 87 to 89. The manufacturer
recommends the use of 89 octane
for optimum performance.

Oddly, it does not say that for the Hemi Magnum. I wonder why. Could it be that Chrysler expects Magnum owners to be more interested in ultimate performance than Aspen SUV owners wfice it to sayould be? Suffice it to say that if you really care about maximum performance and/or maximum economy, you should do your own tests and decide.

[Geoff of NV]

OK, I'm on my third Magnum. Started with a 3.5 liter AWD, next was a Hemi RWD and now a Hemi AWD. I'm anal about checking my mileage (probably as a result of many, many years on motorcycles without gas gauges). All three call for mid-grade gas and although I haven't been able to tell any difference in the way they run with regular, mid-grade and premium, my mileage is always better with mid-grade. Result, I run mid-grade unless it's not available.

[oldyellr]

Originally Posted by Geoff of NV

I haven't been able to tell any difference in the way they run with regular, mid-grade and premium, my mileage is always better with mid-grade. Result, I run mid-grade unless it's not available.

But can you confirm that using "midrange" i.e. 89 octane, costs less per mile than using regular (87 octane)? I'm not interested in ultimate performance except on rare occasions, so will using 89 save me money in the long run or not?

[Geoff of NV]

Cost per mile frankly doesn't interest me. If it did, I wouldn't own a Magnum.