From: Snag_one@msn.com   
      
   On 4/25/2024 11:00 PM, Indira wrote:   
   > Snag wrote:   
   >   
   >>    You might see a slight decrease in gas mileage and power due to the   
   >> slightly retarded spark timing . Modern electronic controls will   
   >> optimize it all .   
   >   
   > Years ago I ran a test on a vehicle which stated it needed premium and I   
   > couldn't "measure" any difference whatsoever in gas mileage, even as I   
   > agree fully with your premise that there "should" be a "slight decrease" in   
   > gas mileage.   
   >   
   > I think the reason I couldn't measure it was that the measurement system we   
   > typically use isn't precise enough because the decrease is too slight. We   
   > measure by the typical method of what I refer to as "gallons used" tests.   
   > a. Fill the tank   
   > b. Drive normally until you need to fill the tank again (note the miles)   
   > c. Fill the tank again (note the number of gallons used & divide miles/gal)   
   >   
   > In my experience, this "gallons used" method isn't precise enough to   
   > measure the "slight decrease" you'd expect from lower octane rated fuel.   
      
      This method is accurate - if you go like 10 tanks the differences   
   average out . One tank at a time will give you a "close enough" mileage   
   number .   
   >   
   > When they really test gas mileage, they put a known WEIGHT of fuel in a   
   > plastic bag attached to the fuel lines, and run that and then weigh the   
   > fuel after a set number of miles. Our gallons-used test is less precise.   
   >   
   > Also, we don't normalize the type of driving, where in general, it's my   
   > understanding, that the only time the "wrong" gas should knock is in when   
   > the spark is advanced which doesn't happen all that often in normal   
   > driving.   
   >   
   > Sure, if you race everyone out of a stoplight, you'll be advanced, but most   
   > normal driving doesn't use spark advance all that much (although all are   
   > advanced - but I'm referring to extra degrees of spark advance situations).   
      
      Your understanding is outdated . Modern controls will optimize spark   
   advance and fuel mixture for the best possible combustion . Now my '86   
   GMC pickup with old fashioned distributor CAN be over-advanced and made   
   to ping . A note about that - the original distributor did have a   
   mechanism to retard spark if a knock was detected . But the block ,   
   heads , and connecting rods are about the only stock parts left .   
   --   
   Snag   
     "They may take our lives but   
   they'll never take our freedom."   
     William Wallace   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)