I freed myself from worrying about gas prices a long while ago - namely when I used to run my 2007 V8 Volvo around, getting 12 mpg city in the WV mountains. Mind you, this is when I was making a whopping $22k/yr in graduate school when premium was $4.00+/gallon. What am I gonna do, not get gas and walk?

But in all seriousness, I've thoroughly enjoyed every mile behind the wheel of the vehicles I've selected over the years (for better or worse), so for me, I'm at peace paying a little more for that happiness

 

I have found the difference between regular and premium to be typically 60 cents per gallon or more.

 

I've run both regular and premium in my P400 and I've anecdotally noticed a significant drop in MPG (1mpg+) when using 87.

 

The main reason most manufacturers specify premium gas is for emissions. The octane rating does not give you more horsepower, but delays the onset of detonation in the combustion process, premium gas burns slower. This allows more latitude in the spark advance. Modern computers have a knock detection, so they sense detonation and retard the spark to keep it from happening. They can also adjust the mixture to a certain extent, leaning or richening it a bit. If you're operating at an altitude of over 5,000' you really cannot get any benefit from premium, since your engine has to lean out to maintain optimum combustion. In aircraft we typically start leaning out our mixtures (which we have manual control over) after 5k' and increasingly more aggressive as we climb. Full rich and optimum spark advance (which is fixed for max hp) is only used in takeoff, when in my aircraft, I pull 300hp for 5 minutes. Something cars almost never do.

So if you're going to go in for emissions testing, yeah fill up with premium. It gives the computer the widest spread for optimum combustion. If you're just commuting, not romping on it, then use what you feel is best, but regular will not hurt it or even diminish the power. If you live up in the mountains like me, then you can certainly use premium, if it makes you feel better, but you can also burn your money as well for warmth. The main reason performance type muscle cars use aviation 100LL is to lubricate their valve guides with the lead (which really helps in high RPM/load conditions), which was one of its many uses aside from retarding composition. I don't think any of you would want to use leaded fuel in your Defender, kind of wastes the catalytic converter.

 

always premium, as pointed out above, there's really not too many dollars to be saved here. when i buy an expensive automobile with a big internal combustion engine, the last thing i'm thinking about is fuel cost

 

Premium fuel has higher mpg than regular fuel so that offsets the saving by using regular.

The price of premium fuel is higher because you are paying for a "premium" product with higher octane and such. That's not a "mark up". A "mark up" would be a higher price for the same product.

 

A few thoughts:

1 - Running premium in newer cars CAN result in higher horsepower, based on the computer adjusting optimally for the change in octane. I haven't seen it for LR, but Ford is pretty clear about horsepower with 87 vs 91 in some of their engines.
2 - The manual for the Defender says they "recommend" premium (91 or higher). Below 87 is engine-damaging territory (Also per the manual).
3 - So they "recommend" premium, but there is also a section that says if you don't hear an engine knock and you end up with damage (regardless of the fuel you're using), it's not warranty covered. There is, of course, much higher risk of a knock with cheap gas. It's a high compression engine with a turbocharger and supercharger, after all.
4 - I run premium. Once I did a partial tank without, because premium wasn't available... so probably mid-grade.
5 - Using prices from a local station today, at 18mpg for 10k miles it's $444 more (93 octane is pricier than 91 octane). The vehicle cost about $75k. I think it's worth it, and while not a rich man, I think I can afford it.

 

Again, how often do you run at wide open throttle? For most folks almost never. The engine will start to throw code for knocking if it does. Most cars run at 20% of their rated power for the greater majority of the time. Even cruising on the freeway, you're not actually pulling that much power. My last car was a supercharged full sized Range Rover, I ran it on 87 most of the time and when I went down the hill I ran mid-grade. It went 14 years without issue and it cost a whole lot more than $75K, $105K to be exact in 2011 dollars. It is still doing just fine, my friend bought it. It is now the Telluride car we all use. Look, the manufacturers put all kinds of stuff in the manual, just to make the regulators happy (how many pages of lawyer warning are in the manual and on every page of the iGuide?). All their emissions testing was done with high test. In the really large engines, ones pulling 2-3,000 hp, multi bank radials, we ran 140 octane, but our timing was fixed and we would pull that 3,000 hp, a lot, they needed it just to stay in the air. Then when we got to altitude we would lean them out to about half the fuel flow or the plugs would foul and they were defiantly drinking gas. Even the antique trainer I trained in (T-28) had a 1420 hp engine and it ran purple fuel (140) and could pull 52" of map as it was two stage supercharged (even had a shifter for high blower at altitude, only plane I flew a lot that had a shifter). They also ran obsencenly high compression, cars that do not race rarely use that ratio. Drag racers and a lot of F1 type cars burn ethanol blends, as it is safer and ethanol retards combustion as well. Just plays havoc with rubber products. During the early days of the fuel crunch, back in the 70's and 80's Brazil ran virtually everything on pure ethanol, which is not exactly high test. Their cars survived, if what you see on the roads in San Palo are anything to judge.

If you're really interested, get a wifi code scanner and an app like OBD Fusion. It will tell you what you pulling in hp real time and show any knocking happening. The new tech is simply amazing. You will get a better sense of what you car is really doing and it will even map your fuel consumption over a route for comparison with repeatable numbers. I would recommend high test, as I have a bunch of stock in the oil companies in my IRA. I have also found, and this is weird, that when I drove back east, my car got worse gas milage. When I went back over the Mississippi, milage would slowly rise. Perhaps they do a slightly different formulation, I know California does, they even seasonally adjust it. It results in lower gas milage as well when I am out there, as much as 10%. Then there is a bit of cheating on what is actually being pumped into your car; is it really high test? There have been enough scandals to give you pause. Gas stations are fairly low margin and actual octane testing is done infrequently by state regulators, they mainly test measurement of what is metered out. At least we color aviation fuel so you can see what you're getting. The only mogas I know that is colored is diesel for non-highway applications, it is red. That's a revenue thing, they watch that closely.

Again, if it makes you feel better go for it.

 

I did indeed make an error. It's currently a 30c difference here. A bigger difference in states with lower regular gas prices would be my guess.

That would make it an approximate $300 saving/year for me and my mileage. I can live with that.

I'm way too much of an idiot when it comes to engines to know what's going on in there so I just stick to the advice on the fuel cap.

 

Interesting torque- and HP-peak comparison of 87-, 91-, 110-and 116-octane Sunoco leaded race fuel, e85, and methanol in a normally aspirated, non-boosted, 6.2 liter Chevy LS3 crate engine.