89 octane recommend, does it really make a difference?

[HSKR R/T]

Because the fuel value of the gasoline doesn't change with octane level. So if the engine can achieve it's preferred timing curve without pinging it will burn the all of them the same resulting in the same numbers.

Without a custom tune it won't reach the preferred timing for the octane level.

 

[RAM Patriot]

Because the fuel value of the gasoline doesn't change with octane level. So if the engine can achieve it's preferred timing curve without pinging it will burn the all of them the same resulting in the same numbers.

You are correct that the BTU is the same for gasoline, but I just want to point out that if you add ethanol fuel to your tank it has about 33% less combustion power, which means you have to burn more fuel for the same amount of power.

 

[RAM Patriot]

Engine Master's on Motortrend just did a study on 87,91,106,116,E-85 fuels on a 10.5 compression hi HP engine and this was exactly their findings. As long as the engine can attain it's optimum timing without pinging, there was no difference in performance.
Engine made 499 torque 540 HP during the test.

Absolutely, Octane is simply the measure of detonation resistance. Detonation is a result of heating and compressing fuel and air until they auto ignite even before the spark plug is turned on.

A higher octane fuel can handle more heat and pressure before combusting.

 

[Timeless]

Why would it be the same? If you understand what the octane number means, and how different octane levels react, you would understand. Granted the normal person may not see enough of a difference to notice, but there is a difference.

Because the fuel value of the gasoline doesn't change with octane level. So if the engine can achieve it's preferred timing curve without pinging it will burn the all of them the same resulting in the same numbers.

Without a custom tune it won't reach the preferred timing for the octane level.

As @RJS said...this is what I am saying. Yes you will not take advantage of the 93 octane. However you will get the same mileage as if you had 89.

 

[HSKR R/T]

As @RJS said...this is what I am saying. Yes you will not take advantage of the 93 octane. However you will get the same mileage as if you had 89.

Not how it works. You won't get as complete of a burn with the higher octane, so depending on where the timing is set you will be sending unburnt fuel through exhaust, and not getting full potential out of the combustion cycle

 

[Fuzznutz]

As @RJS said...this is what I am saying. Yes you will not take advantage of the 93 octane. However you will get the same mileage as if you had 89.

Reading through these post, I don't think anyone ever really doubted what your saying. The huge waste of money they are referring to is pump pricing between 93 and 89 at most places. No benefits from 93 unless you are tuned for 93. Sure it may not be worse economy than 89, but the pump price difference is a waste of money for the same economy.

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[SpeedyV]

Reading through these post, I don't think anyone ever really doubted what your saying. The huge waste of money they are referring to is pump pricing between 93 and 89 at most places. No benefits from 93 unless you are tuned for 93. Sure it may not be worse economy than 89, but the pump price difference is a waste of money for the same economy.

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You might see a small benefit if the pumps that serve 89 aren't doing a good job of mixing, or if your engine happens to run a little more aggressive timing due to tolerance differences. One member on here reported that the computer was pulling timing slightly even on 93, moreso on 89, and much more on 87.

But I'm not disagreeing on your premise, i.e. you're very unlikely to see enough economy advantage on 91/93 to justify the price premium. I did some testing in late 2018 through early 2019; I reported mixed results on this forum. My best economy was indeed achieved on 93, but there were too many variables to presume this was simply due to octane.

Admittedly, I run very low miles now and generally just buy 93.

 

[RJS]

Not how it works. You won't get as complete of a burn with the higher octane, so depending on where the timing is set you will be sending unburnt fuel through exhaust, and not getting full potential out of the combustion cycle

I submit that you should watch the Engine Masters program and then post your thoughts on the issue. The engine they used was 10.5 compression and 540/499 HP/Torque. The setup for the tests determined that the engine did best at 29 degrees total timing and that was found to be the timing the engine preferred for all fuels.

Their conclusions, not mine, were as I said originally. Fuel didn't matter and the engine preferred the same timing for all fuels. I'm just reporting their data witch was gathered with some pretty good dyno equipment and a lot of data gathering.

 

[41magmag41]

Just throwing my 2 cents in, I have 53000 miles on my 2019 Ram bighorn, 4x4, 5.7, 3.92 rear end, regular 8 speed, with 89 octane both winter and summer blend I get 16.5 t0 17.5 mpg. With high test, cheaper at Sam's club than Irving 89 I get 18.9 to 20.5 mpg.

 

[Jabberjaw]

 

[John89]

Hopefully this puts an end to this debate... LOL!

and an end to the people who have been spreading myths as facts! (93 won’t burn all the fuel completely as compared to 89 because of timing etc.)

 

[scottmoyer]

I didn't read all of this and see where some say that RAM recommends 89 for our trucks. I've been running 87 since the day I got it and have about 2600 miles now. My mileage is about 14.5mpg with mostly back road driving (lots of stop and go). I decided to use a tank of Sam's Club 93 since they don't have a mid grade and it was just slightly higher than most station's 87. After about 1/2 a tank, I'm still averaging about 14.5. It might get up to 15, but then it drops again due to stop lights and signs.

I do my best to accelerate gradually and I can't get better than 14.9. Granted, I'm barely broken in at 2600 miles, but my 2006 Silverado Z71 got better mileage with E rated tires and a front end level. I question what my mileage would be if I drove it like I did my Silverado. I'd probably get 12, but I still like the truck and I don't have to drive it daily to work, so I'm good with it.

 

[Jabberjaw]

From my user manual.

 

[Fuzznutz]

From my user manual. View attachment 89511

Ohhhh SNAP!

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[HSKR R/T]

Lost all credibility when he said to use octane booster.

 

[HSKR R/T]

I submit that you should watch the Engine Masters program and then post your thoughts on the issue. The engine they used was 10.5 compression and 540/499 HP/Torque. The setup for the tests determined that the engine did best at 29 degrees total timing and that was found to be the timing the engine preferred for all fuels.

Their conclusions, not mine, were as I said originally. Fuel didn't matter and the engine preferred the same timing for all fuels. I'm just reporting their data witch was gathered with some pretty good dyno equipment and a lot of data gathering.

If that's the case, then should just tune every car to run 87. No need to run higher octane, unless boosted or high compression

 

[Fuzznutz]

I hope I'm still alive when this turns into using premium electricity, vs the poorer grade electricity made for street lights.

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[RAM Patriot]

He summed it up in his last statement. "You should use whatever octane fuel is recommended by your manufacturer."

The HEMI is 10.5:1 compression ratio. 89 octane fuel is recommended for optimum performance and fuel economy by Mopar.

Fuel Based On Compression Ratio

87 Octane
Gasoline with this octane number is proper for engines with compression ratios of 7:1 to 9:1.

89-90 Octane
Gasoline with this octane number is good for engines with compression ratios of 9:1 to 10:1.

93 Octane
Gasoline with this octane number is advisable for car engines with compression ratios of 10:1 to 11:1.

Based on this information our trucks will run optimally with 89-93 octane fuel. Without having to advance or retard the timing.

 

[LakesAZ]

I hope I'm still alive when this turns into using premium electricity, vs the poorer grade electricity made for street lights.

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Or the debate using D batteries over AAA batteries in our electrified Rams. More electrons!

 

[Scram1500]

I hope I'm still alive when this turns into using premium electricity, vs the poorer grade electricity made for street lights.

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The argument will be the source of the electricity. You don't want to be one of those heathens that get from coal or nuclear. You better have green electricity or pay the penalty.... I mean tax