What will 100 octane gas do?

[heyjae]

Originally Posted by Lil bastard

Instead, one of the fuels will be heavier and sink below the other in the tank. First you'll burn one octane until the tank drains it, then you'll burn the second octane. Unless you had an agitator in the tank, or were pulling extremely violent maneuvers (constantly) you would NOT be delivering a dose of each fuel to the cylinders at the same time.

This cannot be true. Gas stations sell 89 octane by mixing 87 octane and 91 octane at the pump (gas stations only have 2 tanks: 1 for 91 and 1 for 87... 3 if they have diesel). They do mix.

[Lil bastard]

Originally Posted by heyjae

This cannot be true. Gas stations sell 89 octane by mixing 87 octane and 91 octane at the pump (gas stations only have 2 tanks: 1 for 91 and 1 for 87... 3 if they have diesel). They do mix.

Well, yes... and no.

Mid-range octane is an alternative. It is the product of not mixing the base stocks of gasoline, but rather the dilutiion of the additives present in higher octane fuel. This is usually a 65.25:1 mix of the premium with regular.

It's more of a marketing alternative than anything. I'm not aware of any car which specifies mid-grade fuel. These are usually designed for premium, but have ECUs which will 'allow' lower grades to be used. Most engine software today follows the principle of 'follow the knock sensor'. That is they run the most retarded spark they can until a knock sensor indicates a need to advance the spark. Since this is done many, many times per second, the driver rarely experiences knock.

I mentioned the need to agitate or mechanically mix the fuels. This is not done in the tank, but at the pump itself with blending valves and so mathematically, complies with the state law that the minimum octane on the pumps sticker is being pumped. But, not any batches of 87 and 91 will do. Only batches from the same refinery and manufacturer, since different brands use different proprietary formulations and chemicals such as MBTE or Ethanol as octane boosters. Not all of these will mix and in some cases will cancel each other out.

The base stocks do in fact separate with time, but with the now dilluted additives attached. If it didn't, gasoline couldn't even be refined since the refining process relies on differing specific gravities to separate the components of crude components.

If you plotted the DMEs spark adavance, you'd see one setting for 65% of the tankful and another for 35% of the tankful. The driver would be oblivious to the different settings because no knock would occur through the tankful.

[23109VC]

this is a total thread hijack, but this is my S60R.... it LOVED 100 octane. I miss this car sometimes...

http://videos.streetfire.net/video/Volvo-S60R-Modified-by_16768.htm

it was a one of a kind. if you go to www.evolvecars.com and look at "the blue car" - i basically did that same car in titanium gray. it turned head whereever I went. it was fairly fast with m y mods - probably about as quick or slightly faster than a bone stock E46 M3. a new 335 with a chip would walk my old car..but 5 years ago - it was "cool".

[conradtan]

Well here's my update. The car stopped belching grey smoke (it does that once in a while on cold mornings) with the 100 octane gas. My mileage stayed the same. No noticable increase in power. The most significant thing I noticed was the temperature of the engine. Usually the needle hovers just to the right of the midpoint of "8" of the 180 degree marker. With this gas, the needle was just a hair shy to the LEFT of the "8". Pretty interesting eh? So... my observation and subsequent conclusion will be I don't think I'll be buying it anytime again soon if all its going to do is run a few degrees cooler.

[Sboxin]

Conradtan: Good summation of your 100 octane experience.

Footnote:
We run 100 in a 1978 track car w/3.2 -- only because our very well experienced Indy told us the engine will run cooler and help the top end last longer. Not spending $13K on a rebuild too soon is motivation enough. But, to put 100 in a street car may not be cost effective.

Thanks,
Ed