Re:How does a gas pump know to shut itself off? (1981)
by TheRealDunkirk on Saturday October 10, 2020 @08:33PM
(#24742974)
To further clarify, the average street car is designed to run on the ethanol which is sold everywhere, but some engine configurations need a higher octane fuel in order to combust the fuel completely. I had a buddy who rebuilt an engine with a compression ratio that required 91 octane, or he'd get knocking. This was during the late 80's, and more than one station around these parts had pumps selling 95 octane (it might have even been 100) for the real hot-rods.
Re:How does a gas pump know to shut itself off? (1981)
by p_l on Sunday October 11, 2020 @05:04AM
(#24744590)
This whole comment thread is surprising to me because I haven't seen sub-90 octane rating in ages - I have even just checked, and one of the main petrol companies in Poland sells only 95, 98, and special extra variant of 98.
Re:How does a gas pump know to shut itself off? (1981)
by saagarjha on Sunday October 11, 2020 @05:45AM
(#24744716)
It’s complicated, as that number measures different things in different countries: https://en.wikipedia.org/wiki/Octane_rating#Measurement_meth...
Re:How does a gas pump know to shut itself off? (1981)
by formerly_proven on Sunday October 11, 2020 @12:36PM
(#24746987)
As per usual, the US uses a different scale (AON) than the rest of the world (RON).
Re:How does a gas pump know to shut itself off? (1981)
by ferdek on Sunday October 11, 2020 @05:41AM
(#24744706)
USA, they have all that weird stuff there...
Re:How does a gas pump know to shut itself off? (1981)
by jakogut on Sunday October 11, 2020 @11:57AM
(#24746648)
> some engine configurations need a higher octane fuel in order to combust the fuel completely
This is incorrect. Higher octane ratings mean a fuel can withstand more compression before detonating. Pre-detonation, or "knocking", where an engine experiences detonation in the cylinder before top dead center can cause severe damage, so higher octane is used with higher compression engines. Lower compression engines see no benefit.
Re:How does a gas pump know to shut itself off? (1981)
by TheRealDunkirk on Monday October 12, 2020 @11:49AM
(#24755664)
If the fuel pre-ignites, proper flame propagation will be thwarted, and the fuel will not be burned as thoroughly, leaving residue, and exhausting (albeit tiny amounts of) fuel. Sure, I put the cart in front of the horse, but I can always count on HN to point out the pedantic.
Re:How does a gas pump know to shut itself off? (1981)
by jakogut on Monday October 12, 2020 @12:06PM
(#24755870)
Reading this again, you're right, it was a little pedantic. This is one of those topics I feel is just rife with misinformation, so I tend to jump on explanations that don't seem correct at first glance.
Re:How does a gas pump know to shut itself off? (1981)
by odonnellryan on Monday October 12, 2020 @12:26PM
(#24756111)
I'm sure this is accounted for, but octane levels do degrade if you don't use your car often. So it can be good to put a higher octane fuel in your car.
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Your vehicle is designed to operate on unleaded gasoline with a pump octane number of 87 or higher. Use of a lower octane gasoline can cause a persistent, heavy metallic rapping noise that can lead to engine damage.
We recommend using gasoline containing detergent additives that help prevent fuel system and engine deposits.
In addition, in order to maintain good performance, fuel economy, and emissions control, we strongly recommend, in areas where it is available, the use of gasoline that does NOT contain manganese-based fuel additives such as MMT.
Use of gasoline with these additives may adversely affect performance, and cause the malfunction indicator lamp on your instrument panel to come on. If this happens, contact your authorized dealer for service.
Some gasoline today is blended with oxygenates such as ethanol or MTBE. Your vehicle is designed to operate on oxygenated gasoline containing up to 10 percent ethanol by volume and up to 15 percent MTBE by volume. Do not use gasoline containing methanol.
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Dealing with the octane number is easy. Just don't use gas with a lower octane than your manual calls for. You can use a higher octane if you want, but it won't really do anything other than cost more. You'll get the same performance, wear, pollution, and mileage as you would with the octane number given in your manual.