Octane for My Hemi

[asand1]

Depends on compression ratio, timings maps, and weight. Run recommended octane or better for optimum mpg and performance.

On a vehicle built before the prevalence of E10 calling for 89 octane, i would run premium.

 

[SteveSRT8]

Originally Posted By: asand1
Depends on compression ratio, timings maps, and weight. Run recommended octane or better for optimum mpg and performance.

On a vehicle built before the prevalence of E10 calling for 89 octane, i would run premium.


I am puzzled.

This is completely counter to experience here. Running more octane is usually worthless. Engines can RETARD timing but only advance it to a specific max value, they do not raise it further just for octane unless they are a flex fuel design.

And E10 is actually good for knock, does nothing to increase it.

 

[asand1]

Originally Posted By: SteveSRT8
I am puzzled.

This is completely counter to experience here. Running more octane is usually worthless. Engines can RETARD timing but only advance it to a specific max value, they do not raise it further just for octane unless they are a flex fuel design.

And E10 is actually good for knock, does nothing to increase it.

My point is that some engines/ecus start from the beginning with more advance. If your timing and compression will benefit from tunning premium or plus then do it.

 

[NHHEMI]

Originally Posted By: Huie83
I used 89 in my Hemi with the cylinder deactivation feature. Seemed like on 87 it would never kick to just 4 cylinders.


My 08 HEMI Ram had MDS and it kicked in no problem running 87. Frankly more than I wanted it to.

 

[NHHEMI]

Originally Posted By: asand1
Originally Posted By: SteveSRT8
I am puzzled.

This is completely counter to experience here. Running more octane is usually worthless. Engines can RETARD timing but only advance it to a specific max value, they do not raise it further just for octane unless they are a flex fuel design.

And E10 is actually good for knock, does nothing to increase it.

My point is that some engines/ecus start from the beginning with more advance. If your timing and compression will benefit from tunning premium or plus then do it.


I had an 04 HEMI Ram( pre E10 )and an 08 HEMI Ram( E10 mandated )and both owner's manuals said not to use more than 89 octain...

2004 RAM 1500 5.7L Octane Rating:
"The routine use of premium gasoline is not recommended. The use of premium gasoline will provide no benefit over high quality regular and mid-grade gasolines, and in some circumstances may result in poorer performance."

2008 RAM 1500 5.7L Octane Rating:
"The use of premium gasoline is not recommended. Under normal conditions, the use of premium gasoline will not provide a benefit over high quality regular and mid-grade gasolines, and in some circumstances may result in poorer performance."

 

[Silverado12]

Originally Posted By: oldhp
We still drive cars in 2094? Geez, you'd think we would be past them by then........


I was promised a flying car by the year 2000 in the 1960's in grade school! Talk about feeling cheated.

 

[Silverado12]

I've experimented in my Challenger 3.5 six and found that 89 makes a difference in how it runs and about 2 mpg better mileage. 93 didn't make a diff over 89.

 

[artificialist]

E10 does different thing to different cars. I have worked on many that have no measurable difference, but it sure makes an impact on my dad's 2007 Pontiac G6 2.4

 

[SteveSRT8]

Originally Posted By: artificialist
E10 does different thing to different cars. I have worked on many that have no measurable difference, but it sure makes an impact on my dad's 2007 Pontiac G6 2.4


Great point. Some posters must have missed that we were having a discussion about a very specific platform. Each mfgr uses different hardware and software to control the engine so there's a huge variable. Then factor in driving habits, fuel quality, age/condition, etc.

The exact same engine could actually like a slightly different grade of fuel depending on a huge set of conditions.

 

[The_Nuke]

Originally Posted By: SteveSRT8
...And E10 is actually good for knock, does nothing to increase it.


My experience with the E10 in D/FW has been just the opposite.

Granted, the excessive detonation I see with E10 is probably due to moisture in the gas due to phase separation or something similar, but the main thing I take away from it is that I would not be experiencing the same amount of detonation with gasoline sans the ethanol.

The Nuke

 

[BillyTheKid]

I have no experience with this specific engine, but from a MPG and power standpoint, I have experienced the following.

Higher octane usually got me very slightly better MPG. I do believe the higher pump octane stuff burns slower.

As for power, the lowest octane used without detonation nets the more power. This is fact unless we start talking funky race fuels, and even the oxygenated race fuel stuff is a very low octane rating (believe around 90). I am also talking normally aspirated engines. So rule of thumb, the lowest octane without detonation shoot for. For the non believers, I have tested and proved this on motorcycles on the dyno numerous times!

I am betting the 87 will make just as much power and close to same MPG, maybe slightly less MPG - so I guess it is time to decide what works best for you for your pocket.

 

[oldhp]

I lose at least 1 MPG when using premium, and this was 3.5 tanks run through it so ECU could read what was going on.