It wasn’t the original question. But since most of the thread seems to have been overrun by a parallel discussion about octane, The Serene Master’s article is appropriate (for the extended hijack subthread).
I guess the “Top Tier Gas” thing is still an open question.
But you’re not running the highest detergent package then. The pump is blending 91 and 87.
I dunno; jet fuel is basically kerosene with some aviation-specific additives, so a spark-ignition gas engine wouldn’t even run on it.
except that you don’t have the knowledge that you’re running the highest detergent package.
none of this bullshit has anything to do with the octane rating your engine needs. But thank you for making it clear that you own a BMW, we’ll make sure that we stay well clear of you since you don’t know what turn signals are and will cut across 4 lanes in one fell swoop.
I think LSLGuy has the answer here.
I do know that all gasoline sold in the state of Minnesota comes into the state on 2 pipelines, and is refined at 2 refineries, and stored in their tank farms. Then tank trucks painted with Shell or Exxon or BP on the side* pull in there and fill up their truck. Each company has their own additives added to the gasoline, but I doubt that they are really much different from one company to the next – they all have chemical engineers working for them, and the chemistry of gasoline & engines is pretty well known.
I know that big fuel users, like the city police department or city streets department or taxi fleets put out specifications for bids each year, and buy from whomever bids the best price – they certainly don’t specify a certain brand name gasoline. I think that there is no significant difference between gasoline brands.
*Actually, now they mostly say “Jones Transport Company” or something similar. Because they often haul to many stations, of various ‘brands’.
Not directly related but affiliated question:
In terms of gas quality how does that come into play with old engines? Say a engine built in 1967. A 289, for instance. Will there be any difference in using regular, super or premium?
This is why I absolutely hate the way gasoline is sold. Even though they are labeled regular, super, or premium, those labels actually say nothing at all about the gas quality. The only difference is the octane rating. Whether or not they put additives or anything into the premium to make it “better” can’t be determined just by the fact that they call it “premium” gas.
An engine built in 1967 may have some significant carbon buildup inside the cylinders, which will tend to increase the compression ratio a bit. This may cause the engine to ping when using the gasoline that it was designed for. An original 1967 289 Windsor is designed to run on 87 octane. If it pings, move up to 89.
If the engine has the original valve seats, you’ll also want to add a lead additive to your gas. The original valve seats were designed for leaded gas, which tended to cushion them a bit from wear. Using unleaded gas without lead additives will cause the valve seats to wear out prematurely. This applies to most vehicles built during the era of leaded gasoline, not just the 289. My old Beetle has the same issue. If you ever get the engine rebuilt, make sure to put in hardened valve seats that are designed for unleaded gasoline.
The lead additive will also boost your octane rating, so if it pings on regular unleaded 87, the lead additive alone may get rid of the pinging.
The actual mechanism of valve seat erosion was micro welds forming between the valve and seat, and as you say the TEL would inhibit the formation of those welds. Once hardened or stellite seats came into use this was much less of a problem.
Moderator Note
Insulting his driving skills just because he owns a BMW isn’t really appropriate in GQ. Pleased don’t do this again.
No warning issued.
He isn’t using ‘jet fuel’. Jet fuel is indeed just kerosene. What he’s using is called avgas. It’s not only high-octane but it still contains lead compounds (TEL) which increases performance. Although banned for cars starting in the 70s (when ‘Unleaded’ was introduced) they are still allowed in aircraft due to the inherent increased danger of bad engine performance while flying. You don’t have to go to an airport, a lot of hot rod shops sell it as racing gas. It’s very expensive, usually two or three times the price per gallon of regular car gas.
So-called ‘Premium’ gasoline is not of any better ‘quality’ than regular. It is merely a higher octane. This also does NOT mean it will provide more power to any engine. All it means is that it will not pre-detonate at a high compression ratio. Unless your engine has at least a 9.5:1 compression ratio premium gas is a waste of money. However, if your car does (and many newer cars do) then it is highly recommended. Even though modern electronic computer controlled engines can compensate for too-low octane gas and prevent actual pinging noise, it’s still not good for them in the long run. And any money you save paying less per gallon not buying premium will be lost by you getting shittier gas mileage.
ETA: forgot to refresh :smack:
@**Jonathan Chance **…
For a simple non-computerized engine it still comes down to compression ratio. The minimum octane which does not knock under your personal driving conditions & habits is all that’s necessary. More octane than that is pure waste. In fact it’s probably reducing available power, not increasing it.
Given the differences between the grades as sold today vs. the grades as sold in e.g. 1967, and also given the highly variable condition of engines that old, I would not put too much faith in whatever spec the manufacturer published way back then. It’d certainly be a place to start, but I’d be willing to experiment higher or lower.
Again, the goal is the *lowest *octane which doesn’t knock under your driving style.
As has been said many times above, but is worth repeating in different words: Modern computer-controlled engines simply override your driving style if you try to drive more aggressively than the current combination of engine, fuel, and weather can handle.
octane rating does not meaningfully affect the energy content or burn rate of gasoline.
I will agree with you 100 percent that octane rating says absolutely nothing about energy content or burn rate.
That said, I’ve also read that higher octane fuels tend to burn slower in a lot of cases. I don’t know enough of the chemistry and physics involved to know if what makes the octane rating higher also tends to make the fuel burn slower or if that just happens to be coincidence for the fuels that we commonly use.
Yeah, I use Mobile 1 (synthetic) oil in my AMG. It’s what MB recommends. I don’t drive 10,000 miles in a year with the AMG so I end up changing the oil on the once a year (or 10K) schedule. With the AMG engine, there are two spark plugs per cylinder so it’s 16 plugs to pull when they need changing. Do I win? 
I also use BG additives/cleaners every other oil change. The dealer and the independent garage mechanics recommend it for the MB. I don’t know if it’s significantly effective given that I burn “top tier” gasoline as a rule. I’m probably throwing $60 away every other oil service but it’s an AMG and I baby the thing; Even more than my commuter car (VW Jetta GLX).
Actually, yes. It is. 
The octane conversation is just incidental.
The octane conversion IS the difference.
Conversation, not conversion.
No, I asked if there was any difference between fuel certified as Top Tier and fuel that wasn’t (i.e. Sunoco) with respect to the added detergents. That question has been answered to my satisfaction.
The octane conversation was a parallel conversation and, as near as I can tell, has little to do with detergents and more to do with using only what’s required by the manufacturer. But with respect to additives, the EPA has ruled that retailers cannot advertise that higher octane fuels contain more detergents that benefit the engine in order not to try to up-sell consumers to higher octane fuels their cars do not require.
Am I mistaken in my take-away from this convesation? If so, in what way?
One nitpick to this: the EPA mandate is just that fuel be oxygenated during the winter. That is most commonly achieved these days with ethanol, but it can also be done with MBTE. California bans MBTE altogether, but I think it’s the only state that does. In other places with the oxygenation requirement, you may still be able to find ethanol-free gas although it will be considerably more expensive.
Ah ha! Now this post I made earlier is relevant:
Montana gas stations typically sell 85.5 octane as the low octane option at the pump. My understanding is that this is related to high altitude, the same mechanics with lower intake atmospheric pressure ends up with slightly lower pressure at the ignition point- so lower octane, easier to ignite gasoline is appropriate.