So, for the sake of experimentation, I ran a tank of 87 through, then put 93 in after wards. Maybe the difference is only in my perception, but it feels like it likes the 93 much better.

Also, SDinDS made a good point....over a tank it's what, ~$5 difference? Maybe $10 over 87....

 

You have it backwards; At high altitude you can go DOWN on octane and will have LESS pinging since there is less air volume being squeezed in. Effectively your compression is lowered at high altitude.
There is a debatable GAIN in performance with a lower octance at higher altitudes since you are correcting for the difference in effective compression. But it would likely be imperceptible.

 

Negative ghost rider.

I'm pretty sure the 4.0 is closer to 9 (9.35 I think)? Hell the 4.4 AJ-V8 in my LR3 is barely over 10:1.

I can think of no reason why a 4.0L V8 that only makes 188hp would EVER need high octane gas, what a freaking joke - the core design is 55 years old!

Sure, perhaps they ROYALLY screwed up with the emissions implementation combined with stupid EFI specs to require a VERY low performance engine to require premium gas, but I still can't stomach putting 93 into it.

I had a 2005 mustang (4.6) that put 305hp to the wheels on a dyno with bolt ons. I COULD PUT 87 IN IT WITH NO PROBLEMS. 300 to the crank stock and it's advertised as being at 87 octane. Sure, Ford is good at designing flexibility into their EFI for lower grade fuels, but from a hardware point of view the engine could care less.

Granted I only use 93 in the LR3, but my DII loves 87 and contrary to what people are saying with these "maybe I'm just imagining it" posts, it DOES get the same or worse (~2mpg at one point) with "better" fuel.

FWIW it's a 99 with 171k on it now I think?

 

MMO addition costs $, to premium $. Same with good tier fuel using same additives?

 

This. All this is what I'm trying to say but "follow the rules" sheep keep saying I'm "ba-a-a-a-ad" for considering something else. Especially since the 4.0 and 4.6 have strikingly different compression ratios, but still require the same fuel grade?? I call BS. Someone mentioned perhaps premium is required for emissions since there is no EGR on these?

 

I don't use premium just to be following the rules. I tried not following the rules and found that premium works better.

These vehicles require it because the computer was mapped for that. It is designed to reduce performance when low octane fuel is used.

I suspect it maybe that on a 4.0l engine which already has lower performance it might be less noticeable.

 

For what it's worth, my neighbor is the ultimate cheap person and has 210k miles, bought a 2002 Disco new and have never put premium and buy the cheapest gas available and oil that the Dollar General sells and no issues other than minors stuff (brakes, hubs, u joints and regular maintenance). I've a Benz 500S notorious for been POS and have 190k miles with ZERO issues with the engine using cheap gas, so you make your own judgement

 

Why would anyone buy a premium vehicle and go cheap on parts or fuel?

Buy a Chevy if you want to be cheap.

 

Going back to the beginning if the thread
"I live at high altitude"
So I wanted experiences from others about taking the octane down to compensate for the lower air pressure.
"premium" doesn't mean better, it means a different octane rating. I don't care about $2 per fill up, I'm interested in what is best for my engine. And cars don't really compensate the best at 7200 feet where I live

 

Broken08, I totally get your original point... and it sounds reasonable to me.

It's the very same reason I use premium in my 4.6 at sea level, It's what works best for my engine.

Pardon my above snark, which was not related to your original point.

It's fine by me if people choose to drive around with retarded timing to save a few nickels, just don't try and tell everyone else that there is "nothing wrong" with it.

For me, I choose to get every available ounce of performance out of my 5000lb brick, which happens to equate to smoother quieter running, more power, and less problem with dirty injectors.