Join Date: May 2009
Location: Vancouver BC Canada
My Octane Mileage experiment
There has been many posts on fuel octane,how they actually effect power production and gas mileage and factory recommendations in the manual,wether its actual fact or warranty liability protection BLAhBlaH Blah.
I have been familiar with all the pros and cons for many years of using different Octane fuels and additives so I did an experiment today on a one hour ride on fairly flat route.Before I start I have a PCV with Ignition adjust and have about 8 to 10 degrees more advance dialed in in the cruising RPM range of 2200 rpm to 3000 rpm in the under 40% throttle positions.I also realize that the average mileage reading is a little optimistic on the dash also,but can be used as a consitent guide in my test run.
I have been using 87 Octane fuel here for the last week or so ,so off I went .I set the speed at 120K (apprx 75 MPH)per hour and set the cruise,rpm was at 2700 rpm most of the way and watched as I hit 55 miles per gallon over a 30 minute staedy run.More often was at 53.X.
When I got to my destination I had about an 1/8th of a tank left and filled it right to the brim with 91 Octane .Started my return trip and got rollin on the freeway,reset the average fuel reading ,locked into 120 K per hour and was surprised to see that I never got above 48 miles to the gallon on the way back.Was mostly at 46.X most of the time.Now I did have a bit of a head wind coming back ,so it may of been about 5% less due to wind issues.I did re test on a short run with no wind issues when I got home and never got above 45 miles per gallon.
A couple other observations with 91 Octane,one being the motor vibration seemed to be more pronounced,like it was not really happy with the new fuel and also there was more exhaust popping on deceleration,proably due to the fact that a lot of unburned gas residue was being exhausted out.Did not have this issue on 87 fuel.Appeared to run slighty hotter on 91 Octane but it was only slightly higher.
I want to do another run on the freeway again ,with 91 Octane,to the same destination again so all things are even steven, and fill up and return on 87 Octane and see what happens.But it appears that my motor is happier on 87 Octane.