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Anyone that’s ever topped off their tank or filled up a jerry can knows gasoline comes in different grades, from regular unleaded to pricey premium. Each “flavor” has a number that corresponds to its octane level, but what does this mean? What is octane and what role does it play? AutoGuide reached out to experts in the fuels field for answers.
See the complete story on octane ratings at AutoGuide.com
 

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my bad- just read it, a little different.

recall in chemistry class we were talking about that (over 30 yrs ago)
we were told isooctane was rated at 100, normal-heptane was rated at zero... neither were mentioned.

got me wondering now, have to do some reading :)
 

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While I realize it's just a rough overview, I feel they really missed the ball by not focusing on heat. Heat was mentioned, but not as the primary cause of auto-ignition. The pressure they focused on is not a primary factor in itself, but the heat caused by pressurizing (compression heat) and other sources of heat such as hot valves and spark plug electrodes are factors octane is designed to battle in the war against heat-induced auto-ignition. In-fact, it is the main focus of engine builders when planning the components and dynamics for an engine that must use a specific det-limited fuel, like a high-performance engine on pump gas.

David
 

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I wanna know where the 93 octane is.
Hmmm think we still have 93 but will hafta look when I go to me soda/gas stop tomorrow.... (just got gas earlier but never pay attention, i zero in on the p1$$ water one....)lol
 

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Even then its still piss water..... bring back the good ole days.... ;) (course i think actually it was the same then just figured differently)

100LL is still avail from the local friendly airport, if ya know a guy....lol
 

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Of course, 100 octane isn't really needed anymore, with advanced tech in Distributor curves and the knock sensors and such tech, there are 11 and 10 second racers on 87 octane out there...

Fast enough on pump gas?
Although tech now allows higher compression ratios with lower octane (I think Ford has some 11+:1 engines that run on 87), to push compression higher to get more efficiency, higher octane is still needed. But, try selling a 40+ mpg that needs 93 octane (or 94 when Sunoco use to have it by me) and I guarantee no one will buy it, even if it got 50 mpg. Diesel is even a tough case thanks to cost/gallon. Imagine an econobox that runs on 100 octane. 13:1 compression would give a gas engine almost diesel-like economy.
 

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some of the ecoboost engines are running around 15:1 with 15 psi boost on top of that!

beauty of direct injection is shooting fuel in after tdc they can get away with 'impossible' things...even without DI, the new 5.0 runs 11:1, and theres quite a few 5psi blowers out there for them...

20 years ago, those numbers woulda been 'impossible', not any more
 

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some of the ecoboost engines are running around 15:1 with 15 psi boost on top of that!
With those numbers, gas engines will finally eclipse diesel engines in terms of efficiency. Never mind getting more with higher octane. What I'm curious to know if GDI changes the cycle from Otto to Diesel. If that's the case, then GDI would be less beneficial than the old MPFI.
 

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How many believe that rating of unleaded 91/92 octane today isnt the same as unleaded 91/91 octate as 25 or more years ago

thats it wont give the same anti knock protection at the same compression ratio .
 

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How many believe that rating of unleaded 91/92 octane today isnt the same as unleaded 91/91 octate as 25 or more years ago

thats it wont give the same anti knock protection at the same compression ratio .
It could be if a different method was used to rate it. There's the RON, MON, and R+M/2 method (most ratings here I see have used the latter, and is the average of the former two). I forgot which (RON or MON) gives the higher numbers (which is why Europe's higher numbers aren't that much higher than ours when converted). Also, with the push to lower prices as of late, I wouldn't be surprised if quality took a dive.
 

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It could be if a different method was used to rate it. There's the RON, MON, and R+M/2 method (most ratings here I see have used the latter, and is the average of the former two). I forgot which (RON or MON) gives the higher numbers (which is why Europe's higher numbers aren't that much higher than ours when converted). Also, with the push to lower prices as of late, I wouldn't be surprised if quality took a dive.
the R+M has been around since the 70's . testing methods are the same/not changed

more than once I hear the unleaded to isnt as good as the old day unleaded . To me , WTF are they talking about ,the new 91/92 can't run as high of a comp. ratio as the old 91/92 . Thats just one more b/s story
 
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