- Joined
- Dec 7, 2020
- Posts
- 6,891
- Reaction score
- 17,445
- Location
- Minneapolis, MN
- Ram Year
- 2017 2500 Laramie Crew Cab
- Engine
- 6.4L HEMI
What does optimum performance mean and why would they use those words in the owners manual? You can use 87 and there likely wont ever be an issue, but it is not optimum performance. Neither is 91, but I use 91 because costco here doesnt sell 89.
And here I was doing to ask if you could tell a difference between 89 and 91.
They still sell 89 octane up here, with 10% ethanol only, state-mandated (as is 87 octane). So, I can tell it runs smoother on 89 / 10 than 87 / 10. Did not try 91 because supposedly the engine won't advance ignition timing further to take advantage of it, and without that it leaves more unburned deposits.
The moral of the story is to run the lowest octane your engine has ignition timing advance setting. Many tuners have a 91 or higher octane power setting that will advance ignition timing further. I have that too, just not interested in a race truck. I use the tow setting which still calls for 89 octane.
Another interesting tidbit in Minnesota - state law allows sale of 91 octane pure gas for sensitive engines - motorcycles, outboards, chainsaws, other 2-strokes, etc. State law prohibits using 91 octane pure gas in modern vehicles, yet there is zero enforcement. Usually there is just one or two pumps of this small engine gas at a station, but stations also sell 91 octane with 10% ethanol for high compression and/or turbocharged engines like wifey's Mazda that prefers it.
Finally, the ethanol mafia in Minnesota bribed the legislature to promote 88 octane with 15% ethanol gas, along with E85 which is 85% ethanol for 'flex fuel' engines. This is all just agri-processor giant bribery of government. Food grown for fuel. The culprits here are Cenex (CHS now), Archer-Daniels-Midland (ADM), and Cargill. I watched it develop working for Onan / Cummins.