89 Octane vs 91/93 Octane performance in my HEMI

DDC · Nov 22, 2015

I just ran 2 tanks of 91 Octane in my 2011 HEMI and my D ran totally different in a bad way. I've switched back to 89 Octane and my D feels like its supposed to. anyone else experience this?

I run a HT Interceptor, Volant intake and stock exhaust. I changed the plugs to oem Mopar Police Package plugs just about 3,000 miles ago.

there is a Sams near my office that sells 91 Octane for just about what you can buy 89 Octane at a bunch of other stations. I've bought 91 Octane from this Sams for years so I'm confident it's not just bad gas. I used to have a Dodge Intrepid R/T with the 3.5L HO that recommended 91+ Octane and I always filled up at this Sams. and Sams goes through gas pretty fast in my area so I don't think it was just a bad batch of gas.

performance tapered off gradually with the first tank, probably since I usually fill up once the tank drops to 1/4 full. it was funny, near the middle of the 2nd tank of 91+ Octane I found myself doing the throttle reset twice! I was like 'what is going on here?' it finally occurred to me it could be the 91 Octane. I switched back to 89 and just finished a tank and refilled.

D runs like its supposed to now.

Skippy426 · Nov 22, 2015

Mine runs the same on 93 as it does on 89. Does not really like 87 that much. I run 93 just because it seems like it gets 1-2mpg better on it than it does on 89. Could be winter blend vs not winter blend?

pat515001 · Nov 22, 2015

Higher octane WILL provide worse performance. Do a quick Google search on what octane actually is. Unless you have upped the compression ratio on your motor, higher octane will have zero performance gains.

Run what is recommended.

drewby12 · Nov 22, 2015

Our vehicles are tuned for 89 octane. Unless you have a tuner specifically for high octane, you're not going to reap any benefit at all from putting he expensive stuff in it.

Natet510 · Nov 22, 2015

drewby12 said:
Our vehicles are tuned for 89 octane. Unless you have a tuner specifically for high octane, you're not going to reap any benefit at all from putting he expensive stuff in it.

Is that true, the 5.7 Hemi is tuned to 89 octane? Can you let me know where you got this info. I tend to fill up at Costco since they are usually 10-25 cents cheaper than anyone else, and they only offer 87, and 91 here in CA.

I already know the use of octane as a combustion suppressant for higher compression engines, but didnt realize the stock tune was tailored to 89.

drewby12 · Nov 22, 2015

Says in the owners manual verbatim that 87 is "tolerated" but 89 is "recommended". Our computer is designed to retard timing when lower than recommended octane is used, so you can get away with using 87; however, when using higher than 89 octane, the computer will not advance timing for performance reasons past the factory 89 tune. If you're going to choose between 87 and 91, use 87. 91 will not yield anything performance or fuel economy wise without a tune.

Bryali · Nov 22, 2015

pat515001 said:
Higher octane WILL provide worse performance. Do a quick Google search on what octane actually is. Unless you have upped the compression ratio on your motor, higher octane will have zero performance gains.

Run what is recommended.

Do another quick Google search because you are only partly correct. You don't have to raise the compression in an engine to get more power, you just have to retune the spark timing. Without tuning, you WILL NOT get any gains but that doesn't mean you will get worse performance. Running 91 in an engine tuned for 89 will perform exactly as if you are running 89. It won't run any better or worse. Changing the spark timing doesn't turn a 9:1CR engine into a 11:1CR engine but you'll still make more power.

However, I you are correct that you should run whatever you are tuned for or 89 for stock tunes.

tomk · Nov 22, 2015

Also, you need to run for many tanks to let the PCM relax.. it will rapidly take out timing, but takes a long time to let it come back.

That said, I've never had that severe of a performance drop going to higher octane, even in an old-school carburated V8.. so I don't quite know what's up there..

DDC · Nov 23, 2015

tomk, its a matter of losing its zip. yes, you could characterize it as backing off the timing. but if its as simple as timing, why would 91 Octane have an impact over 89 Octane?

engine still ran smooth, no issues there. just did not feel like it usually does. and now back to 89 Octane it feels like it should.

QuantizedKi · Nov 23, 2015

My D runs on the tears of Honda Pilot owners.

Skippy426 · Nov 23, 2015

2011CrewLuxSC said:
tomk, its a matter of losing its zip. yes, you could characterize it as backing off the timing. but if its as simple as timing, why would 91 Octane have an impact over 89 Octane?

engine still ran smooth, no issues there. just did not feel like it usually does. and now back to 89 Octane it feels like it should.

Okay I know this sounds kinda like an insult but... Are you sure you hit 91 and not 87? I've come across a few pumps that were "backwards" and 93 would be on the left and 87 on the right.

Imagine my horror as a broke high school student when I clicked 93 and didn't notice till it was almost full...

Islandiver · Nov 23, 2015

The difference between 89 and 91 is marginal, I would think the Hemi has a knock sensor, so untill it hears Knock it should keep advancing timing untill it hears it. The deal with premium fuel is that if you believe the pump it run's more or better deposit additives, The down side is that because 93 resists detonation better there is a slight lag in ingnition of the fuel itself. Dodge may cap and alter timing map's based of the 89 fuel profile to get smoother operation where as a 93 map is more aggressive in timing based on it's profile. The other thing you have to ask yourself is are you always getting the fuel you paid for ? most gas stations only have a 87 and a 93 tank the pump actually blends the fuel to make 89.

pat5150 · Nov 23, 2015

Bryali said:
. You don't have to raise the compression in an engine to get more power, you just have to retune the spark timing. Without tuning, you WILL NOT get any gains but that doesn't mean you will get worse performance.

I simply omitted the spark timing info..without a tuner, it's a non issue. CR info just for example.. The two really go hand in hand. I agree with you..

I run a drag bike where timing can be changed trackside, and CR can be changed simply by gasket thickness.. Obviously not that easy on a durango.. That said, the speed at which higher octane burns vs. Lower, in this case, IS marginal. But, this motor is built, timing and CR, for 89.

I could see a small dip in performance, especially an 87 car running 91 or 93 on the mythical higher octane=more horsepower thought process.. Especially if an onboard computer can only advance timing so much. Or at all.

DDC · Nov 24, 2015

Skippy426 said:
Okay I know this sounds kinda like an insult but... Are you sure you hit 91 and not 87? I've come across a few pumps that were "backwards" and 93 would be on the left and 87 on the right.

Imagine my horror as a broke high school student when I clicked 93 and didn't notice till it was almost full...

no insult taken, its a fair question. but no I'm sure. this is a Sams Club gas station I've purchased gas at for 10+ years. and Sams only has two buttons 87 and 91. they don't offer 93 or 89. its pretty idiot proof. now, did maybe the tanker driver accidentally fill the 91 tank with 87? that's possible.

Skippy426 · Nov 29, 2015

2011CrewLuxSC said:
no insult taken, its a fair question. but no I'm sure. this is a Sams Club gas station I've purchased gas at for 10+ years. and Sams only has two buttons 87 and 91. they don't offer 93 or 89. its pretty idiot proof. now, did maybe the tanker driver accidentally fill the 91 tank with 87? that's possible.

Ah... That's the only thing I can think of then. I very rarely fill up with "top tier" gas, usually only got the "local" stations like Family Express, Speedway, or a Luke station. I will say that my Durango did not like the local Meijer gas... Mpg went to 11, down from 13!!!

Robfrmny21 · Nov 29, 2015

I used 4 tanks of 93 when I first got it and then went on to 87 till present day.

The throttle response was better with the 93 i.e. Less spark retard under load but the rango still just as fast up top with either fuel.

I ran a v6 rango at a light and beat the snot out of it with 87.
The torque is still a neck snapper. Be honest performance difference is marginal at best on a stock tune.

FSTDANGO3 · Nov 29, 2015

I have observed knock when using off brand 93 octane rated fuels so I cant imagine what off brand 87 or 89 actually sees.
For the AVG Person no change will be felt. I try and run only top tier as it truly is better fuel.
STEVE

89 Octane vs 91/93 Octane performance in my HEMI

DDC

Skippy426

pat515001

drewby12

Natet510

drewby12

Bryali

tomk

DDC

QuantizedKi

Skippy426

Islandiver

pat5150

DDC

Skippy426

Robfrmny21

FSTDANGO3

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