macbuddy
04-10-2010, 06:13 AM
91 Octane vs 87 Octane, which is better?
THE QUESTION
I have seen several threads claiming that the OP experienced advantages to using 91 octane fuel over using the recommended 87 octane. After searching several threads concerning this practice, I found no conclusive answer. Most of the claims were offered as unselfish tips for others to benefit from. However, in most cases, these OPs were "flamed" for wasting time and money, as the ECUs of the Honda Fit could not make use of the additional octane.
DEFINING "BETTER"
The practice sounded intriguing to me, so I decided to find out for myself. First, I had to determine what "better" really meant. To me, better would mean either better fuel mileage, better performance, and/or better cost per mile.
THE GOAL
My overall mpg average ever since getting the Fit back in April 26, 2006, has been ~33.5 mpg. My goal was to see if using 91 octane would make any deference in any of the following 3 categories:
1) fuel mileage
2) performance
3) economy
FUEL MILEAGE (Pass or Fail?)
Pass- In order to prove "better," I would need to see any increase in mileage. For me, fuel mileage would have to be better than ~33.5 mpg. This could be beneficial if I were on a 425 mile trip, and I wanted to make sure that I could confidently do so on one tank. This would make the additional $ .20 per gallon worth the extra cost to me.
Fail- If I see a definite decrease in mileage, I would consider this a "failed" practice.
PERFORMANCE
Pass- In this category, I would need to detect any significant "seat of the pants" difference.
Fail- If I detect any decrease in drive-ability, I would consider this a "failed" practice.
ECONOMY
Pass- To prove "better" in this category, I would need to see at least a 2.5 mpg increase.
Fail- If I see less than a 2.5 mpg increase, I would consider this a "failed" practice. Otherwise, upgrading to 91 would not compensate for the extra $0.20 per gallon. If 87 octane costs $3.00/gal, and yields 33.5 mpg, then it costs me about $0.089/mile. To break even, I would have to get at least 36 mpg to justify using 91 octane. At $3.20/gal, 36.0 mpg would also give me $0.089/mile.
THE PLAN
My plan is to burn through no less than 4 full tanks of 91 octane before arriving at a conclusion. My method is to fill the tank until I can see fuel in the "neck" of the filler tube. Then I will drive until the "fuel light" is lit. At my earliest convenience, I would again refill the tank to the "neck" with 91 octane, and repeat the process until the end of the 4th tank of fuel.
THE DATA (odometer reading from 98,313 miles to 100,164 miles)
3/29 Valero 91 octane 406.3 miles / 11.180 gal = 36.34 mpg
4/02 Safeway 91 octane 458.5 miles / 13.680 gal = 33.64 mpg
4/03 Costco 91 octane 481.7 miles / 13.053 gal = 36.90 mpg
4/06 Exxon 91 octane 504.5 miles / 15.325 gal*= 33.64 mpg
http://img249.imageshack.us/img249/6543/pict0083e.th.jpg (http://img249.imageshack.us/i/pict0083e.jpg/)
4 tank summary 1,851.0 miles / 53.238 gal = 34.77 mpg
CONCLUSION
After 5 days of driving, and 4 full tanks of 91 octane, I would have to say that using 91 octane proved to be uneventful.
1) Fail-I was not able to achieve the +2.5 mpg necessary to justify the extra $0.20 /gal cost.
2) Passed-Although I did not feel a significant performance advantage while driving those 4 tanks of 91, I was surprised to feel a difference after refueling with 87 octane. I immediately experienced a noticeable hesitation at takeoff.** I had apparently gotten acclimated to the better "launch" of the 91 fuel. I liken this to using my very responsive Macintosh computer. I don't really appreciate how well it works until I use a "slower" machine. I routinely notice that when going from a "slower" computer to a "faster" one, I don't really don't notice the speed increase because it's merely responding like it is supposed to!
3) Passed-Although I did not clearly see a marked fuel consumption advantage, an extra 1.27 mpg is an extra 1.27 mpg. In my GD3 with it's tiny 10.8 gal tank, finding an open gas station on a lonely freeway at 3:00 in the morning could be a lot less stressful with that extra 13.7 mile cruising range.
NOTES
After testing 53.238 gal of 91 octane, I think that I will revert to 87 octane. I did not see enough gain to make the switch. The 1.27 mpg increase was hardly a convincing jump. Those four tanks cost me an extra $10.65 to go an extra 68 miles. Had I used that money to get 87 octane, that would have bought me 3.55 gal of regular. 3.55 gal @ ~33.5 mpg would have given me ~119 miles, or an extra 51 miles for the same money.
*note:
1st tank, When I saw 36.34 mpg on this tank, I thought I was on to something!
2nd tank, I was surprised to see 13.680 gal go into my tank!
3rd tank, 481.7 miles was the farthest I had ever gone on one tank! (picture) (http://img684.imageshack.us/i/mailzt.jpg/)
4th tank, I added 3 gal on Chevron to get me home. Their 91 was $3.439/gal. I didn't want to fill the tank at that price.
**As for the hesitation when reverting to 87, that sensation may have been due to the ECU not having enough time to adjust to the lower octane.
-macbuddy-
PS-My Fit just turned 100K!
THE QUESTION
I have seen several threads claiming that the OP experienced advantages to using 91 octane fuel over using the recommended 87 octane. After searching several threads concerning this practice, I found no conclusive answer. Most of the claims were offered as unselfish tips for others to benefit from. However, in most cases, these OPs were "flamed" for wasting time and money, as the ECUs of the Honda Fit could not make use of the additional octane.
DEFINING "BETTER"
The practice sounded intriguing to me, so I decided to find out for myself. First, I had to determine what "better" really meant. To me, better would mean either better fuel mileage, better performance, and/or better cost per mile.
THE GOAL
My overall mpg average ever since getting the Fit back in April 26, 2006, has been ~33.5 mpg. My goal was to see if using 91 octane would make any deference in any of the following 3 categories:
1) fuel mileage
2) performance
3) economy
FUEL MILEAGE (Pass or Fail?)
Pass- In order to prove "better," I would need to see any increase in mileage. For me, fuel mileage would have to be better than ~33.5 mpg. This could be beneficial if I were on a 425 mile trip, and I wanted to make sure that I could confidently do so on one tank. This would make the additional $ .20 per gallon worth the extra cost to me.
Fail- If I see a definite decrease in mileage, I would consider this a "failed" practice.
PERFORMANCE
Pass- In this category, I would need to detect any significant "seat of the pants" difference.
Fail- If I detect any decrease in drive-ability, I would consider this a "failed" practice.
ECONOMY
Pass- To prove "better" in this category, I would need to see at least a 2.5 mpg increase.
Fail- If I see less than a 2.5 mpg increase, I would consider this a "failed" practice. Otherwise, upgrading to 91 would not compensate for the extra $0.20 per gallon. If 87 octane costs $3.00/gal, and yields 33.5 mpg, then it costs me about $0.089/mile. To break even, I would have to get at least 36 mpg to justify using 91 octane. At $3.20/gal, 36.0 mpg would also give me $0.089/mile.
THE PLAN
My plan is to burn through no less than 4 full tanks of 91 octane before arriving at a conclusion. My method is to fill the tank until I can see fuel in the "neck" of the filler tube. Then I will drive until the "fuel light" is lit. At my earliest convenience, I would again refill the tank to the "neck" with 91 octane, and repeat the process until the end of the 4th tank of fuel.
THE DATA (odometer reading from 98,313 miles to 100,164 miles)
3/29 Valero 91 octane 406.3 miles / 11.180 gal = 36.34 mpg
4/02 Safeway 91 octane 458.5 miles / 13.680 gal = 33.64 mpg
4/03 Costco 91 octane 481.7 miles / 13.053 gal = 36.90 mpg
4/06 Exxon 91 octane 504.5 miles / 15.325 gal*= 33.64 mpg
http://img249.imageshack.us/img249/6543/pict0083e.th.jpg (http://img249.imageshack.us/i/pict0083e.jpg/)
4 tank summary 1,851.0 miles / 53.238 gal = 34.77 mpg
CONCLUSION
After 5 days of driving, and 4 full tanks of 91 octane, I would have to say that using 91 octane proved to be uneventful.
1) Fail-I was not able to achieve the +2.5 mpg necessary to justify the extra $0.20 /gal cost.
2) Passed-Although I did not feel a significant performance advantage while driving those 4 tanks of 91, I was surprised to feel a difference after refueling with 87 octane. I immediately experienced a noticeable hesitation at takeoff.** I had apparently gotten acclimated to the better "launch" of the 91 fuel. I liken this to using my very responsive Macintosh computer. I don't really appreciate how well it works until I use a "slower" machine. I routinely notice that when going from a "slower" computer to a "faster" one, I don't really don't notice the speed increase because it's merely responding like it is supposed to!
3) Passed-Although I did not clearly see a marked fuel consumption advantage, an extra 1.27 mpg is an extra 1.27 mpg. In my GD3 with it's tiny 10.8 gal tank, finding an open gas station on a lonely freeway at 3:00 in the morning could be a lot less stressful with that extra 13.7 mile cruising range.
NOTES
After testing 53.238 gal of 91 octane, I think that I will revert to 87 octane. I did not see enough gain to make the switch. The 1.27 mpg increase was hardly a convincing jump. Those four tanks cost me an extra $10.65 to go an extra 68 miles. Had I used that money to get 87 octane, that would have bought me 3.55 gal of regular. 3.55 gal @ ~33.5 mpg would have given me ~119 miles, or an extra 51 miles for the same money.
*note:
1st tank, When I saw 36.34 mpg on this tank, I thought I was on to something!
2nd tank, I was surprised to see 13.680 gal go into my tank!
3rd tank, 481.7 miles was the farthest I had ever gone on one tank! (picture) (http://img684.imageshack.us/i/mailzt.jpg/)
4th tank, I added 3 gal on Chevron to get me home. Their 91 was $3.439/gal. I didn't want to fill the tank at that price.
**As for the hesitation when reverting to 87, that sensation may have been due to the ECU not having enough time to adjust to the lower octane.
-macbuddy-
PS-My Fit just turned 100K!