Question about fuel octane level.

[joesstripclub]

Straight from my 2020 owners manual. I don't want to "hear a light knocking sound from the engine".

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This is interesting as my 2021 just says to use 87 octane.

 

[Riccochet]

This is interesting as my 2021 just says to use 87 octane.
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All they did was remove the part that said to use 89 for optimum performance and fuel economy, and changed the recommendation to 87. Directly above what you snipped it still says you might hear a light knocking sound. If you're ok with a light knocking sound and the ECU pulling timing that's your decision.

I run top tier premium 91-93. I paid for 405 HP, I want 405 HP.

 

[joesstripclub]

All they did was remove the part that said to use 89 for optimum performance and fuel economy, and changed the recommendation to 87. Directly above what you snipped it still says you might hear a light knocking sound. If you're ok with a light knocking sound and the ECU pulling timing that's your decision.

I run top tier premium 91-93. I paid for 405 HP, I want 405 HP.

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Yep you are right. Strange why they would change the verbiage there. Was hoping I got away from needing higher quality fuel when I moved up to the 6.4.

 

[NewBlackDak]

The best mileage and power I had in my 6.4 was running 89 E0. I live at an elevation where normal is 85 Regular/87 Midgrade/89 Premium. Non ethanol can be had in 88/89 and occasionally 91. I run the 91E0 in my boosted snowmobiles, but never in my truck since it's by far the most expensive fuel at any pump around here. It was fine running 85 unloaded, but unloaded didn't happen often.

 

[Docwagon1776]

This is interesting as my 2021 just says to use 87 octane.
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6.4L was designed as a fleet work engine. It has lower compression is less aggressive in pursuit of top end power in the name of longevity and total cost of operation, as well as the lesser emissions requirements for HD trucks. Also beefed up cooling passages to keep cylinder temperatures more consistent.

It's designed from the ground up for 87.

 

[Dusty]

Yep you are right. Strange why they would change the verbiage there. Was hoping I got away from needing higher quality fuel when I moved up to the 6.4.

There's an unwarranted assumption that there is absolutely no difference in mechanicals or timing spec's between the two years. There could be a difference that prompted a change in the owners' manual.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 135097 miles.

 

[Docwagon1776]

There's an unwarranted assumption that there is absolutely no difference in mechanicals or timing spec's between the two years. There could be a difference that prompted a change in the owners' manual.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 135097 miles.

There's also an assumption that all parts of an entity as large as a major automobile manufacturer know and communicate all information to all other parts of the entity in a timely and correct fashion. They don't write a brand new manual for every model or even every vehicle, they modify an existing one.

In other words: The manual isn't infallible and may have been cut and paste of the 5.7L until the error was discovered and corrected. *MAY*. Or maybe not, but I think it's a reasonable supposition.

 

[Sherman Bird]

There's an unwarranted assumption that there is absolutely no difference in mechanicals or timing spec's between the two years. There could be a difference that prompted a change in the owners' manual.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 135097 miles.

Potato, Potahto?

 

[Dusty]

There's also an assumption that all parts of an entity as large as a major automobile manufacturer know and communicate all information to all other parts of the entity in a timely and correct fashion. They don't write a brand new manual for every model or even every vehicle, they modify an existing one.

In other words: The manual isn't infallible and may have been cut and paste of the 5.7L until the error was discovered and corrected. *MAY*. Or maybe not, but I think it's a reasonable supposition.

Equally true.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 135129 miles.

 

[joesstripclub]

6.4L was designed as a fleet work engine. It has lower compression is less aggressive in pursuit of top end power in the name of longevity and total cost of operation, as well as the lesser emissions requirements for HD trucks. Also beefed up cooling passages to keep cylinder temperatures more consistent.

It's designed from the ground up for 87.

We were comparing 2020 6.4 to 2021 6.4, so in theory same engine. Why in 2020 was it 87 or 89 but 2021 says 87?

 

[Docwagon1776]

We were comparing 2020 6.4 to 2021 6.4, so in theory same engine. Why in 2020 was it 87 or 89 but 2021 says 87?

There's also an assumption that all parts of an entity as large as a major automobile manufacturer know and communicate all information to all other parts of the entity in a timely and correct fashion. They don't write a brand new manual for every model or even every vehicle, they modify an existing one.

In other words: The manual isn't infallible and may have been cut and paste of the 5.7L until the error was discovered and corrected. *MAY*. Or maybe not, but I think it's a reasonable supposition.

Note that early manuals did not distinguish between 5.7 and 6.4L, nor did the 2500 have a different manual than the 1500. The manual was simply for Ram trucks, lumping the 1500/2500/3500 together. 2019 is the first year the HDs get broken out into their own manual.

If we want to take the manual as gospel, it also recommends *against* anything higher than 89 in the earlier manuals:

5.7L/6.4L EnginesThis engine is designed to meet all emissions regulations and provide satisfactoryfuel economy and performance when using high quality unleaded gasoline havingan octane range of 87 to 89. The manufacturer recommends the use of 89 octane for optimumperformance. The use of premium gasoline (Over 89octane) is not recommended, as it will not provide anybenefit over regular gasoline in these engines.

 

[ozzysdad]

I have been running premium since gas has been more affordable.
When I ran 87 exhaust tips were always black with soot.
My guess is timing is retarded with lower octane to prevent knocking.

 

[Sherman Bird]

I have been running premium since gas has been more affordable.
When I ran 87 exhaust tips were always black with soot.
My guess is timing is retarded with lower octane to prevent knocking.

So, black soot is a benchmark?

 

[joesstripclub]

Note that early manuals did not distinguish between 5.7 and 6.4L, nor did the 2500 have a different manual than the 1500. The manual was simply for Ram trucks, lumping the 1500/2500/3500 together. 2019 is the first year the HDs get broken out into their own manual.

If we want to take the manual as gospel, it also recommends *against* anything higher than 89 in the earlier manuals:

5.7L/6.4L EnginesThis engine is designed to meet all emissions regulations and provide satisfactoryfuel economy and performance when using high quality unleaded gasoline havingan octane range of 87 to 89. The manufacturer recommends the use of 89 octane for optimumperformance. The use of premium gasoline (Over 89octane) is not recommended, as it will not provide anybenefit over regular gasoline in these engines.

Makes sense if the ECM can't adjust past 89 to not recommend it. Premium in a lot of places is no-ethanol so some guys see a big benefit/better mpg from it but thats not really because of the octane. Good info on the manuals only recently being separated out, your point of carry over language could definitely be applicable.

 

[nascar72]

It needs it because of the high compression.

Use it.

You paid good money for that truck. Do you want to risk damage to save a few $

Though 89 is recommended, 87 will definetely not hurt it under daily driving and higher than 89 is a waist of money because there will be no difference...at least for the third gen hemi anyway. Maybe with the newer 6.4s you may feel a difference with higher octane though.

 

[nascar72]

Makes sense if the ECM can't adjust past 89 to not recommend it. Premium in a lot of places is no-ethanol so some guys see a big benefit/better mpg from it but thats not really because of the octane. Good info on the manuals only recently being separated out, your point of carry over language could definitely be applicable.

I've had an '03 1500 with the 5.7 and now have an '08 2500 still with the 5.7 and tried all grades and seen absolutely no difference in either mileage nor performance. Now, that being said, I will run 87 for my daily routine stuff, about 80% of the time and will run 89 when pulling my 8k lbs 5ftwheel camper 2 weeks a year to make sure to prevent preignition knock.

 

[Bigskyroadglide]

It's been my experience since my first ram in 2011, best fuel economy is achieved by using 89 octane or greater and E0. My rams average about 18 to 19 mpg. I'm happy with that number.

Ive had a few to correlate my data.

 

[Riccochet]

^^^ agree. 89 and non-ethanol if I can find it has treated me the best for all of my Ram's.

 

[Sherman Bird]

I was reading through the owners manual and noticed this Ram calls for 89 octane instead of the usual 87 on past year Rams. Why the difference and is it worth it? Thanks everyone.

Other than subjective answers you get here, you'd have to obtain a good scanner with flight recording function, drive the truck through a drive cycle, and read all the data germane to fuel management and correction. Otherwise, go by the manufacturer requirement to be safe.

 

[Wild one]

Other than subjective answers you get here, you'd have to obtain a good scanner with flight recording function, drive the truck through a drive cycle, and read all the data germane to fuel management and correction. Otherwise, go by the manufacturer requirement to be safe.

HP will do the same thing