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Discussion Starter · #1 ·
When i got my manual i never thought twice about putting 93(top grade in my area) octane in it and im not sure how but i thought it was required even though the cap and filler door doesnt have any octane requirement on it i can find. Then i was reading some random thread, cant remember which one where everyone was talking about how they were using 87 octane and im like, i can use 87?? Just to be sure i yanked out the manual for my 2009 and it has different octane requirements, 87-89 for auto and 91 for manual. so i still need 91 but now im curious why? Is there a factory tune difference in the earlier challengers or do autos come with some sort of octane adjustment tuning?
 

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2021 Challenger RT Shaker 5.7 Hemi
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Same question, I have. New owner of 2021 Challenger RT Shaker, 5.7 Hemi.
 

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2016 R/T Scat Pack
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Same tuning. I believe it's a safety precaution as you're more likely to rev higher between gears with an M6.
 

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Discussion Starter · #4 ·
Same tuning. I believe it's a safety precaution as you're more likely to rev higher between gears with an M6.
Ok i can see that, but then a new question is do autos with the manual shift option also require 91? Or do autos just have a lower rev limit and the manual(auto) shift still gets limited to that lower limit? It just kind of seems wierd that two basically identical engines have different requirements, especially when you consider the 2 octane difference between the 89 and 91 requirements.
 

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I'm always mystified on the "octane debate" and why anyone would consider running less than the highest grade fuel available? On the 16 gallon fill up and a .50 differential that is only $8 which is typically less than anyone would pay for a single lunch or a 6 pack of cheap beer.

I get economy but I don't understand buying a high performance car (then often modding it for more speed spending hundreds or thousands) and chinsing out on the fuel.
 

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Discussion Starter · #6 ·
I'm always mystified on the "octane debate" and why anyone would consider running less than the highest grade fuel available? On the 16 gallon fill up and a .50 differential that is only $8 which is typically less than anyone would pay for a single lunch or a 6 pack of cheap beer.

I get economy but I don't understand buying a high performance car (then often modding it for more speed spending hundreds or thousands) and chinsing out on the fuel.
i tend to play that cents is only dollars game too when i stop at a more convenient station instead of the cheaper station. My truck takes 87 and is tuned for it and cars tuned for lower grades can suffer form higher grades(or so i hear). More importantly though for me the truck has a 26 gal tank and at 17mpg those 50 cent differences start to climb quite high when filling up. So thats why i myself consider and o run lower grades, but now realize you probably meant in relation to challengers only.
 

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2021 M6 Shaker RT
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Engine speed does not change octane requirements. The tune does. With a higher octane fuel being used, the tuner or manufacturer can be more aggressive with the timing table to get a few more HP. If lower octane is used then recommended, spark knock may occur and the knock sensors sense this and pull timing. Most PCMs will pull the timing and keep it that way until it sees a refueling event, which is not the same as putting 16 ounces of octane boost. You can't fill it with 87 then go get the octane boost, it may be too late and inaudible knock has already occured on the run to the parts store.

Running higher than required octane hurts nothing, except your wallet. The higher grades do usually contain more detergents however.

A higher octane fuel is harder to ignite, that is why it resists knock.
 

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M6 5.7s have more aggressive timing, (which accounts for the higher power and torque ratings) so 91 octane is required

the A5 /A8 5.7s can use 89 octane

the only Challenger engine rated for 87 octane would be the 3.6 V6
 
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Discussion Starter · #9 ·
M6 5.7s have more aggressive timing, (which accounts for the higher power and torque ratings) so 91 octane is required

the A5 /A8 5.7s can use 89 octane

the only Challenger engine rated for 87 octane would be the 3.6 V6
my manual states the 3.5 and 5.7 auto together as 87 "acceptable" - 89 recommended, but thats besides the point. I didnt consider the auto had different hp ratings then manual and that would explain it completely and make sense.
 

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Recommended octane levels are to prevent engine knock. I have experienced knock when stalling out my 5.7 M6 while starting out in first gear, even when using 93
 

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2021 Challenger R/T Hellraisin M6
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I'm always mystified on the "octane debate" and why anyone would consider running less than the highest grade fuel available? On the 16 gallon fill up and a .50 differential that is only $8 which is typically less than anyone would pay for a single lunch or a 6 pack of cheap beer.

I get economy but I don't understand buying a high performance car (then often modding it for more speed spending hundreds or thousands) and chinsing out on the fuel.
Prices in my neighbourhood in Canada (you'll have to deal with metric measurements):
$1.35/L - 87 octane
$1.67/L - 91 octane

Using your logic, when filling up a full tank (~65 L) you're looking at a $21 difference to just use the highest grade available. That's a pretty hefty difference for majority of people for literally 0 benefit if they're tuned for 87 gas.
 

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It's the MDS!!! :ROFLMAO:
 

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2015 RT 5.7 M6
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Here is WOT timing of M6 vs Auto (M6 timing - A8 timing).
Rectangle Font Red Screenshot Parallel


This is full advance (lockpin) WOT spark.
Colorfulness Rectangle Font Screenshot Parallel


WOT power enrichment. This is an adder to stoich. It also kicks in when the pedal voltage is 3V on an M6 and 3.16V on an A8.
Rectangle Font Screenshot Parallel Technology
 

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Prices in my neighbourhood in Canada (you'll have to deal with metric measurements):
$1.35/L - 87 octane
$1.67/L - 91 octane

Using your logic, when filling up a full tank (~65 L) you're looking at a $21 difference to just use the highest grade available. That's a pretty hefty difference for majority of people for literally 0 benefit if they're tuned for 87 gas.
Yep. 21 is a lot of money each time. Our Canadian brothers have it hard. I live in Texas where we make oil (when our government is not shutting down pipelines) so premium 93 is pretty easy to come by.
 

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Recommended octane levels are to prevent engine knock. I have experienced knock when stalling out my 5.7 M6 while starting out in first gear, even when using 93
This is the reason imho, it's simply a hedge against detonation and to protect the engine against those who refuse to downshift and lug the engine. The automatic transmission has no such concern, it will downshift as needed but the manual has no built in protection.


Sent from my SM-N960U using Tapatalk
 

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This is the reason imho, it's simply a hedge against detonation and to protect the engine against those who refuse to downshift and lug the engine. The automatic transmission has no such concern, it will downshift as needed but the manual has no built in protection.


Sent from my SM-N960U using Tapatalk
But then why wouldn't the MDS (A8) engines run the same WOT timing as the non-MDS (M6)? They are different as I show the amount of timing difference above between the 2 engines with the M6 engine running overall more timing.
 

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2020 Dodge Challenger Hellraisin Scat Pack
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A higher octane fuel is harder to ignite, that is why it resists knock.
That's not right. Octane is the fuel's ability to resist detonation. To do so high octane gasoline is "designed" to resist forming ignitable compounds ahead of the spark triggered flame front from the increase in heat due to the increase in pressure and radiation (light). But once the flame front reaches the unburned gasoline molecules they "instantly" form ignitable compounds from the heat of the flame front and then with handy oxygen molecules burn.

Because of this timing can be advanced which starts the combustion process earlier which results in the combustion pressure pushing on the piston at its optimum point in its travel down the cylinder so more of the chemical energy from burning gasoline is converted to mechanical energy.
 
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