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I searched and couldn't find this discussed already. The owner's manual says 87 octane is acceptable and 89 is preferred. So when I first got my Charger Daytona 5.7L I was using 87. Since then an article was published in Car and Driver magazine where they compared performance differences between the different grades of gas, as it relates to several cars, one of them being a Charger R/T with 5.7L engine. They found that the performance hit was minimal when using 87 octane gas and the savings were significant. It's hard to argue with these findings. However, I notice a big difference in performance and drivability, not just between 87-89, but also between 89-93. 93 seems to be the ideal, running smooth like one would expect a modern fuel-injected engine to do. With 87 or 89 there seems to be some hesitation and/or frequent lulls in power delivery. With 93 I can "light 'em up" any time I want. 87 and 89 seem to be slower off the line. Opinions?
 

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The lower the octane the sooner the knock sensors pull timing. Seeing as 93 is the higher octane it is the slowest to pull timing which would mean less performance.
 

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Discussion Starter · #3 ·
I think you have that bass acwards. When the system senses knock it pulls timing, which causes a notable hesitation and lower performance. This would happen with the 87 octane, but not the 93, which is why is seems so much smoother/faster when I run 93 (Which is probably what you meant!). But according to car & driver, the difference is minimal. Maybe my 5.7L is an anomaly.
 

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I searched and couldn't find this discussed already. The owner's manual says 87 octane is acceptable and 89 is preferred. So when I first got my Charger Daytona 5.7L I was using 87. Since then an article was published in Car and Driver magazine where they compared performance differences between the different grades of gas, as it relates to several cars, one of them being a Charger R/T with 5.7L engine. They found that the performance hit was minimal when using 87 octane gas and the savings were significant. It's hard to argue with these findings. However, I notice a big difference in performance and drivability, not just between 87-89, but also between 89-93. 93 seems to be the ideal, running smooth like one would expect a modern fuel-injected engine to do. With 87 or 89 there seems to be some hesitation and/or frequent lulls in power delivery. With 93 I can "light 'em up" any time I want. 87 and 89 seem to be slower off the line. Opinions?
In the Car and Driver article, 14 HP was lost with the 87. I wouldn't really call that minimal.
 

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I think you have that bass acwards. When the system senses knock it pulls timing, which causes a notable hesitation and lower performance. This would happen with the 87 octane, but not the 93, which is why is seems so much smoother/faster when I run 93 (Which is probably what you meant!). But according to car & driver, the difference is minimal. Maybe my 5.7L is an anomaly.
Not really because the 87 would be the first to get knock and the 93 the last or slowest to get knock and have timing pulled.
 

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Bass Ackwards, heh! I see it too.
The whole deal is to run as much timing advance, and as lean air/fuel ratio as you can without pre-detonation.

Premium does not burn hotter or is more explosive, it resists pre-detonation or flashing off from hotter combustion chambers before the spark is commanded.
So if you are having timing advanced being pulled/retarded (KR = knock retard)its to save your engine.
Lots of people waste cash on premium. In some cases loose power. My tuner tells me MOPAR 5.7 knock sensors can be overly sensitive. No two engines are the same but he sees it often and has to tweak them.

A stock 5.7 will only advance timing so much. If you run 101 octane it will not advance more than it does for 89. There is a set limit in the OE tune. So when you run more octane than 89 you are only getting the max advance they setup for 89.

If your car seems to run better on 93 go for it. No two engines are the same. Maybe it pulls more than it should on 89 on your particular car. A noisy valve train can cause KR.

I have a supercharged silverado and a dyno tuned 5.7 and use HPTuners. I have experience working with spark on chevy 5.3's analyzing scan logged WOT runs to see what points in the run they pull and tweak individual cells in the tables. I hours spent battling KR.

Don't forget about intake air temps too. Its getting cooler now and they love it. I checkup scan log WOT runs on my rides every August to see how they are doing in the heat to make sure they are not pulling spark.
 
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In the Car and Driver article, 14 HP was lost with the 87. I wouldn't really call that minimal.
I wouldn’t call a 14hp and 23 lb-ft loss from running 87 minimal either, but the tested impact on vehicle performance – acceleration, anyway – was indeed minimal. I was shocked when C&D testing showed such little differences in acceleration when running low octane: 4.9 sec 0-60 stayed the same, 0-100 the car was 0.2 sec slower and 1/4 mile was only 0.1 slower (same 106mph though.) It makes me question the value of that Scat Pack Stage 1 kit which adds 18 horsepower and 18 lb.-ft of torque. It seems you could get similar HP and more torque - with little difference in acceleration - just by running 93.
 

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Go ahead and run 93 octane. It’s your money. Personally, after 6 years and 134,000 miles, I do not notice a seat of the pants or driveability difference. I will use 89 once in awhile because I feel guilty about sticking with 87 but I only run 93 if I’m going to run at the track...which may be once per year. I have as good running of a bone stock 5.7 as anyone and it lives fine on 87 octane. I know it might like 89 better but definitely does not need 93 for daily driving.
118641
 

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Nice, what gear ratio do you have?
 

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Copy that. Curious because my 2.65 gears won't do that good. Love the gas mileage and I run up top more anyway.
 

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Seems to get pretty good gas mileage with the 3.06. It averages around 21 mpg every day around town but this was a couple of years ago about 150 miles into a 200 mile one way trip to Virginia Beach from N. VA. It will have a range of up to 500 miles on a trip.
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Copy. I like your times. If mine ever needs replacing it'll be a 3.06.
 

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Seems to get pretty good gas mileage with the 3.06. It averages around 21 mpg every day around town but this was a couple of years ago about 150 miles into a 200 mile one way trip to Virginia Beach from N. VA. It will have a range of up to 500 miles on a trip. View attachment 118650
That is phenomenal mileage! My 2015 R/T Road & Track has 3.07 gears and I get around 14.5 mpg city/24 highway. No mods and I'm pretty easy with it.
 

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It depends a lot on how much stop and go traffic and how you drive. I guess I try to take it easy for the most part and drive in cruise control about 75-79 mph on the interstate. I got 25 mpg in my Hellcat driving from Virginia to Chrysler’s at Carlisle the last time I took it.
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