[email protected] (Dave Williams)
fords  02 Aug 1994
- -> Higher octane gasoline burns more slowly, so the trick with an octane
  -> booster would be to add heavier or longer chain (or aromatic)
- 
  Octane doesn't have anything to do with burn rate or flame front
  speed; it's just a measure of the fuel's resistance to detonation.
- Some higher octane fuels may indeed burn more slowly than lower octane
  fuels, but it's not common and not related to octane rating.

[email protected] (Dave Williams)
2strokes  06 Aug 1994
- The octane scale was established in 1929 using two typical
  hydrocarbons as reference fuels.  One was normal heptane (n-heptane,
  C7 H16) which had a very low resistance to detonation, and iso-octane
  (C8 H18), which was far better than any commercially available
  gasoline at the time. The two fuels were assigned values of 0 and 100.
- The Research Octane Number (RON) and Motor Octane Number (MON) were
  established in the mid-30s.  They are measured in exactly the same
  way in the CFR engine, but the temperatures and speeds are different.
  Research octane ratings around 70 were available in the mid-'30s.
  Both automobiles and motorcycles typically used special fuels for
  racing, normally home blends of alcohol, toluene, benzine,
  nitromethane, and aviation gasoline.  Tetraethyl lead may have been
  used by some of the big teams like Mercedes or Auto Union, but Ethyl
  Corp. and others have always been very reluctant to sell the additive
  in pure form.
- The US Federal Trade Commission mandated all gas pumps had to have
  octane ratings posted on them by March 15, 1972, but 34 oil companies
  sued, delaying things.  The pump ratings didn't appear until the
  middle of 1979, as the R+M/2 rating, which was originally called
  "AKI", or "Anti-Knock Index."
- British fuel is rated in RON, while American fuel is rated in R+M/2.
  The same fuel would have a higher rating at a British pump than in an
  American pump.

[email protected]
hotrod  Nov 07 1994
- I was flipping through the July/August issue of Summit's catalog before
  throwing it out.  In the "Tech Tips" section they have an mini-article
  called "Cheap Gas Wins Races."
- "Your racing engine really doesn't care how much you paid for your gasoline.  
  All it cares about is if the gas has sufficient octane to prevent 
  detonation." 
- True.
- "In fact, giving your engine more octane than it needs may cause power to 
  drop off - as octane increases, burn rate decreases." 
- Lord preserve us, now Summit is pushing that line of bullshit.  Octane 
  rating has NOTHING to do with burn rate!  Where do these people keep getting 
  this stuff?  Can't they look it up and check before publishing this crap?! 
- "For example, burning high dollar, high octane racing gas in a 9:1 
  compression engine results in a bunch of unburned hydrocarbons dumping out of 
  the headers." 
- Say what, Bubba?  That doesn't even make sense.
- Now I know where the wreck.autos.tech goobs get this drivel, anyway.

[email protected] (Dave Williams)
fordnatics  14 Sep 1995
- -> My 95 Mustang GT says it is made to run with an octane rating of 87.
  -> I put in 93 octane.  Am I wasting money doing this?
- Yes.  Once your fuel is of sufficient octane to prevent detonation, putting 
  in higher octane fuel achieves little.  There is no difference in power 
  between the two fuels unless a substantial portion of the octane increase 
  comes from crap like MTBE or methanol, which can reduce the energy value of 
  the fuel by as much as 25%  That's for engines without knock sensors. 
- *However* if you have a car with a knock sensor, you *may* see better 
  mileage and power with a higher octane fuel.  Some chips continually keep 
  the spark advance tweaked up against the detonation limit, even at cruise.  
  This typically makes more power, which lets you back out of the throttle a 
  bit, which saves gas, and also gives you that power back when you need it.  
  A friend and I did some chip testing in his car and found two tenths on the 
  strip between 87 octane fuel and 93 octane with a dose of toluene.  We also 
  found just cranking the static advance acheived the same performance 
  increase as the chip, for free.   
- I don't know if your car has a sensor or not, but given the difference in 
  price between premium and regular gas around here - nearly 27 cents per 
  gallon - you're spending a lot of extra money every time you fill up. 

[email protected] (Dave Williams)
gnttype  28 Jan 1996
- -> Another thing, we all talk about bad gas.  We all need a certain
  -> octane. Is a testing kit available that will let us test the effective
  -> octane of the gas we buy??  That way the gas variable is then know.
- Octane is measured empirically, by running the fuel in a standardized 
  Waukesha variable-compression single cylinder test engine. 
- Unfortunately, the test basically determines how well the fuel does in a 
  Waukesha test engine, not in your particular motor.  It's quite possible to 
  find "88-octane" fuel that won't knock in your motor, while the same brand 
  of "91-octane" fuel will rattle your cage. 
- In most vehicles this sort of stuff doesn't matter much, but when you're 
  running 15psi of boost conventional ratings go to hell in a handbasket. 
- Bruce Hamilton has compiled an enormous and detailed Gasoline FAQ which can 
  be found in various places.  Bruce knows his stuff pretty well, but he 
  doesn't have a lot of hands-on experience with cars, and he has a bad 
  tendency to take "expert reports" at face value, particularly if they're 
  from big, important sources, and no amount of real-world data will convince 
  him otherwise.  He also has distinct ecoNazi tendencies. 
- In any case, his FAQ is a good source of information, and contains 
  invaluable pointers to other sources. 

[email protected] (Dave Williams)
gnttype  28 Jan 1996
- -> They say in the article that you fill your tank with 40 to 60% 87 octane
  -> fuel then add the rest at say 92 octane. the article says that you would
  -> think that this would make the octane somewhere between 92 and 87 octane
- That sort of thing *was* true... about fifteen years ago, when you could mix 
  leaded premium and unleaded regular and get a higher rating than the 
  straight premium.  The early unleaded fuels were actually a better grade 
  than the leaded premiums; premium doped cheap gas with loaded of tetraethyl 
  lead.  Anyway, mixing gas worked after a fashion, though it gave station 
  attendants fits. 
- The whole thing became a nonissue when leaded premium faded away. Nowadays, 
  up to half of what comes out of the pump might not even be gasoline at all - 
  some areas pump the fuel full of alcohols, dissolved butane, ETBE, MTBE, and 
  God alone knows what. 
- The Buick's closed-loop EFI takes care of a lot, though it can't get a 
  smooth idle on really crummy gas.  A bad case, though, would be if you were 
  right up against the limits of your stock fuel system.  You know you're on 
  the edge of going lean, maybe thinking about new injectors or diddling the 
  line pressure, but you know the car is okay.  Then you fill up at a 
  different place, and you're running 20% lean due to heavy contamination with 
  oxygenates, and you give the knock sensor a workout next time you put your 
  foot in it.  Hopefully you don't damage anything else.  MTBE is brutal to 
  rubber hoses and plastic fuel system parts. Alcohol can cause corrosion in 
  the injectors. 

[email protected] (Dave Williams)
gnttype  20 Mar 1997
- -> I could be wrong, but octane ratings have nothing to do with
  -> peformance directly.... some high octane fuels tend to have less
  -> specific gravity, depending on what they use for an octane additive
  -> and I can understand where this may actually result in slightly less
  -> fuel economy.  Also, this would lead to slightly less BTU/gal.
- You're correct.  The major issue, though isn't specific gravity per se, but 
  the composition of the fuel itself. 
- In the Good Old Days, gasoline was pretty much gasoline.  The only 
  difference between a low octane gas and a high octane was how much 
  tetraethyl lead it contained, unless it was one of the very few brands that 
  used a higher base cut and different additive package.  If you weren't 
  pinging on regular, the only thing Ultra Blue Ethyl Supreme would do would 
  be to empty your wallet faster.  Though the resulting change in power-to-
  weight ratio would theoretically give you better ETs, I doubt it made much 
  difference in practice... 
- Nowdays you get a witches' brew roughly similar to camel urine.  Most brands 
  and areas (gasoline is blended for geographic areas according to climate, 
  altitude, season, politicial[oxygenate or reformlate] and other specifics) 
  you're getting the same "regular" gasoline at each pump, with alcohol, ETBE, 
  MTBE, or other "octane improvers." 
- Alcohol will lean you out a bit, but at the usual <10% inclusion you're 
  looking at, oh, (swag) 3 or 4 percent leaner, max.  The trouble comes with 
  ETBE and MTBE, which act as both oxygenates and octane improvers. You can 
  get a tank full of "gasoline" little better than kerosene or bug remover, 
  laced with alcohol, and the remaining 30% or so being various tertiary butyl 
  ethers, which are a *rotten* motor fuel.  They're cheaper than gasoline, 
  taxed at a cheaper rate (which the gas company keeps as profit), make the 
  Greenies happy, and can knock even closed-loop EFI systems flat on their 
  keister.  It's not in the least uncommon to come across "premium" fuels 
  which will cause a car to run like crap. Carbureted cars - the ones they're 
  usually claiming the oxygenates benefit - sometimes won't run *at all*, and 
  if they do, the percentage of lean misfire drives HC through the roof. 
- The trick to all this is, the *TBE-contaminated fuel passes the SAE octane 
  rating test in the standard Waukesha single cylinder test motor, so that 
  resulting 90, 91, or 92 "octane" rating gets stuck on a batch of juice 
  that's really *less* suitable as a motor fuel than the "regular" fuel sold 
  at the adjacent pump. 
- As long as you're talking apples and apples, a higher octane fuel's only 
  difference is that it will allow you more boost, compression, or spark 
  advance, which will allow you to make more power.  In practice, it's apples 
  and camel piss, and the "high octane" fuel can make a car fall flat on its 
  face. 

[email protected] (Dave Williams)
Ford  07 May 1998
-> different than yours), but for a motor to perform near optimum you
-> don't want too much octane, either, if its not needed.
- Once you have enough octane (rating, not chemical) more doesn't help. 
  Doesn't hurt, either. 
- However, if the octane rating is acheived by doping a low grade fuel with 
  oxygenates like MTBE, ETBE, or alcohols, it'll throw off your fuel/air ratio 
  to the lean side, which can be disastrous on a race motor.  Spark advance 
  requirements also change for oxygenated fuels. Not a good idea to run that 
  kind of swill in a race car. 
- Some octane-boosters-in-a-can use MMT.  It supposedly isn't used in pump gas 
  any more.  If the plugs start coming out with brown-red crusties, the fuel 
  likely has MMT in it.  Don't even try to run a race car on the stuff; it 
  promotes combustion chamber deposits among other things.  Drain it and give 
  it to someone you don't like. 

[email protected] (Dave Williams)
Ford  10 May 1998
- -> Since higher octane fuels burn slower, I thought I was probably
  -> *worse* off running the Turbo-blue on the 10-1 motor of yore.  True?
- Um.  That one keeps coming back, complete with hockey mask and machete, like 
  something out of a third rate horror movie.  I believe I saw it in a Summit 
  "Professor Overdrive" a few catalogs ago. 
- Octane rating has *nothing whatsoever* to do with how fast the fuel burns.  
  It's a rating of how sensitive the fuel is to detonation.  Some higher 
  octane fuels might or might not burn at a different speed than a given low 
  octane fuel, but that's a function of the petroleum fraction used and 
  whatever the fuel is doped with, not anything directly related to the octane 
  rating. 
- It's like saying "red cars are faster than green cars."  Well, maybe some 
  are, maybe some aren't, but the color (or octane rating) doesn't have 
  anything to do with how fast they are. 
- A useful reference for this sort of stuff is "The Internal Combustion Engine 
  in Theory and Practice" by Charles Fayette Taylor, from MIT Press.  Sir 
  Harry Ricardo's "The High Speed Internal Combustion Engine" is out of print, 
  but you can probably get a copy on inter-library loan. Ricardo's book 
  predates the octane rating system, but it has a lot of fuel data that's 
  still useful. 

[email protected] (Dave Williams)
Ford  13 May 1998
- -> One question...  If higher octane fuels burn at the exact same rate
  -> as lower octane fuels, then why does an engine that is optimized for
  -> lower octane need to have it's timing advanced to be optimized for
  -> race-gas?    .....even when the compression is low enough that
  -> detonation is not a problem with either fuel.
- You have to know if you're comparing apples and apples or apples and horse 
  apples. 
- For straight cut fuels (simple distillates), a high and low octane fuel will 
  have the same flame speed and take the same amount of spark advance, given 
  that the CR is low enough not to pin on either fuel. 
- Where you get horse apples is, "high octane" is normally achieved by 
  processes other than straight cuts, which faded from the market long ago.  
  Until a decade or so ago most fuels were the same basic cut, except octane 
  boost was achieved with tetraethyl lead.  Again, flame speed and spark 
  requirements were the same. 
- Nowadays all bets are off.  What comes out the 87 octane pump can be, and 
  often is, vastly different than that comes out the 91 octane pump. Even if 
  they're both the same brand from the same station.  Many modern high octane 
  fuels are heavily doped with oxygenates, which screw up the AFR and God 
  alone knows what.  A lot of the stuff you get from the gas station nowadays 
  is less than 75% gasoline; the remaining 25% can be ethyl or methyl tertiary 
  butyl ether, methanol, ethanol, butane, asphalt, or "proprietary" additives.