Such high compression ratios—and the premium fuels that go with them—could be turned to efficiency, rather than speed, Green notes, especially if put into the engines of lighter cars like his Honda Civic. Other automotive fuels, such as ethanol, can also offer high octane ratings, allowing oil companies to use more volatile gasoline in such blends. But for standard cars on the road today, purchasing premium gasoline is simply paying a premium for a fuel that delivers no added benefits. "If you think you need it," Green says, "you're being very eccentric."

Note: This article was changed after publication to correct an error. It originally stated that heptane has 14 hydrogen atoms.

6 Comments

1. 1. Billstecko 05:59 PM 6/5/08

   Since engine timing is governed by the Erasablble prom, where can I get a prom re-programmed to utilize regular gas on my 2001 3.6 Outback?

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2. 2. Saltyal in reply to Billstecko 07:42 PM 5/18/09

   If your engine has high compression ratio, requiring higher octane (slower burning fuel) then changing your ignition timing & fuel delivery with a different ECM & regular gas probably won't produce any benefit.
   
   this message uses 100% recycled electrons

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3. 3. ecstatist 10:37 AM 9/19/09

   OVERSIMPLE clarifications (rule of thumb)
   "premium" = self esteem felt with purchase of x.
   true value = miles (kilometers) per buck.
   -
   the denser the fuel (approx = average molecule size) the further you go per unit volume (gallon) = not greater than 0.5-1% per "octane" (compare consequent price increase)
   therefore lowest octane without knock = best value.
   alcohol = relatively lower density (but raises octane) "do the math"
   -
   combustion: best = predictable "slow" and complete burn allowing maximum useful energy to be extracted
   knock = explosion = high speed combustion due to burn caused by fast "(super?)sonic" high pressure wave front progressively igniting mixture.
   advertising marketing = extracting maximum bucks for minimum value! while making sucker feel good.
   
   

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4. 4. JonBirge 03:01 PM 5/14/10

   The definition of knocking is incorrect. I believe knocking is when the combustion front doesn't progress evenly from the point of ignition, such that pockets of fuel/air burn in advance of it, causing higher than normal peak pressures in the cylinder and essentially messing with the timing. This causes the "pinging" sound and rough running, but won't destroy an engine unless is happens for a long time. What the article describes--ignition due to compression alone--is actually called detonation, and it will destroy and engine very quickly. You won't get a pinging sound, but more of a loud diesel sound followed by the sound of your engine falling apart, I'm guessing.

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5. 5. arejay 11:58 AM 6/28/10

   I believe that a service station has been selling regular gas in place of premium and of course increasing their profit. How do I discriminate between premium and regular or have fuel tested to prove my suspicion. Ron

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6. 6. jimfromcanada 11:33 AM 3/7/11

   No, pinging IS preignition or detonation, and is destructive to engines.
   Modern engines generate a lot of power from small capacity by the use of the fine tuning that electronic ignition and fuel injection allows. So they are always operating on the edge of detonation when being pushed as in high speed highway driving, heavy acceleration, or hauling large loads.
   Having destroyed a couple of engines by using low octane fuels in such situations I always use at least mid grade when highway driving or towing a trailer. It is much cheaper than rebuilding an engine.

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