So would it be better to use ethanol free gasoline with a lower octane or a premium grade with ethanol and a higher octane in my 2020 Defender ?

 

Feel free to test this on yours, I won't on mine.

I've driven Audi's for years and all of them required 91 (or whatever, 93, etc) premium gas. Most of the engines were tuned to 91 and didn't adjust down. We had a shortage in 2015-ish time frame and after a call to the Audi dealer and the Audi service line their response was 'don't, it will not be cool for you' when I couldn't find premium anywhere for a few weeks.

Those that did put 87 octane in were reporting knock/pings at idle not just when you put your foot in it.

Everything I've read in my obsession waiting for the car says the same results will happen. You have a supercharger and a turb on this thing, and it's built for 91 octane. I won't experiment with it. I still remember the experience of 'just use unleaded' when leaded gasoline was removed and I drove an old chevy truck that needed regular. going to 87 from 91 octane caused run ons, knocks, pings, and some impressive backfires if you rev'd the engine

I believe you will ruin the seals if you try that E85 or whatever it goes by on the LR engine.

Fords are different, they sell their performance cars at the 91 octane gas rating, but let you put 87 in as their computers adjust based on detected octane. They also are built for that 'gasohol' or whatever it's called now 'blended fuel' but I never found any and was never brave enough to try as when I did find it was on a road trip in the middle of nowhere.

 

just use premium, high-octane gas as recommended.

 

Here are few things to consider that I've learned in my 3+ decades in this industry:

* Octane = stability = resistance to radical combustion. It means the ability to stomp on the pedal and advance ignition timing and get the most out of the fuel.

* Modern engines, meaning like every major automotive engine in the last decade or two have some form of knock detection. Originally they were piezoelectric sensors on the block that generated a voltage from the vibration when knock occurred. Many in later years moved to ion sensing along the secondary ignition spark circuit. Same result though, when knock was detected timing is retarded and HP is reduced.

That's a lot of tech speak but what it mostly means is that modern engines can usually adjust to lower octanes, they just produce less HP that way. So check your owner's manual and you'll see what you can do.

E10 ethanol isn't an issue for these vehicles.

Using non-ethanol might offer a slight mpg advantage but that's about it.

Afaik there's no reason we can't use 87 (US ratings) but 91 is recommended for best performance. If you're not going WOT or stomping the throttle you can probably use octanes that are lower than recommended. More so at altitude, though the turbo/supercharger reduce that a bit.

 

And just to add to Kev M's comment above, higher octanes do not equate to higher HP. It's the engine management adjusting the timing that effects the HP. Higher octanes resist early detonation and allow for greater timing advances to optimize HP. Engines that do not automatically adjust timing will achieve the same HP on 87 octane as on 120 race fuel. (This hard to kill urban myth about octane and HP is a pet peeve of mine.)

 

ABSOLUTELY.

An engine CAN make more hp on a higher octane IF it is designed to do so (by advancing timing to maximize burn time) but this doesn't happen on all motors. A lot is determined by factory design and tune.

I'll go one step further.

I believe our P400 is rated for US 91, which means it DOES NOT make more hp or run better or do anything better on US 93.

As a matter of fact, running an octane ABOVE your rating can increase emissions (and create excessive carbon deposits long term) and waste fuel. You may even see worse mileage depending on the disparity in fuel and ratings.

 

Here is the recommendation and explanation from our Defender Bible (the manual). Premium (min. of 91 octane).
"Using a lower specification fuel may reduce the vehicle's performance, increase fuel consumption, cause an audible engine knock, and other driveability problems.

 

If you can afford to buy a Defender then you can afford to put premium fuel in it. Also look for top tier gas such as Exxon, Mobil & Shell. Here is a list:

https://toptiergas.com/licensed-brands/

Edit: Kev M you are correct - By "premium" I was referring to 91 or 93 octane gas.

 

Yeah but I hate just using the term "premium" as it is not precise.

It leads some, uh let's say "overly-enthusiastic but less mechanically inclined" members of the population to think things like "Well if 91 (R+M/2) is good, then 93 is better, but then if I can get 100ll AV gas or 110 race fuel that must be the best" etc.

Also at altitude you might not even find 91 sometimes, and people start un-necessarily worrying about using a lower grade.

Or maybe I'm just a bit retentive because my career is literally built upon being precise with this type of information. lol.

 

Thank you for shedding some logic to this discussion. There is not a production engine built today that does not have the appropriate knock sensors/timing retard ability...For one very good reason: Emissions.