Canuck

Definitely not using the same station, nor would I on my return trip, going to whatever station is available at the exit I happen to take, but trying to stay with name brand outlets, the one time I couldn't the results were surprisingly bad. Again not a scientific conclusion but it was worth noting (IMO).

BTW - the requirement to provide a ZIP code at some stations is PITA when all you have is a Postal Code

esmarkey

If it's a debit card try running it as debit and then you only have to put in your PIN. Just curious, what happens when you put in your Postal code?\


Also, I know we are an anal bunch and we are always giving suggestions and second guessing, etc. Don't let that get to you, just post a summary of what YOU find when you are all done. It is interesting.

mistermike

The decrease in mileage with lower octane is generaly due to the mild knock causing the ECM to decrement the timing toward the low octane spark table. 0% is fully mapped to the low table, 100% is fully mapped to the high table. It is not an inherent quality of 87 octane fuel to produce less economy than high octane, as any comparison of fuels in a car NOT tuned for high octane will attest. In fact, in a "normal" car, high octane fuel will generally produce a slight decrease in economy.

Monitoring knock retard is essential when making these type of comparisons. Without it, the results have no validity. When I first got my GTO, I ran a few experiments with low octane fuel while monitoring KR and octane scaler data with EFI Live. What I found was that as long as KR wasn't induced, the economy actually was better with low octane fuel, but the techniques required to keep the car out of KR made it very difficult to drive. You had to accelerate as if there was an egg under your foot, otherwise the resultant knock pulled all the spark timing, and economy along with it.

esmarkey

You mentioned:
"In fact, in a "normal" car, high octane fuel will generally produce a slight decrease in economy."

I have heard this before, what is the reason for this?

catdaddy137

i will refill in the mourning. i drive the exact same route everyday. most everyday , -early morning - not much traffic , the weight of my load may vary. the weather will be about the same , 25-39 deg. i have drove it enough to get a good average , -27mpg at 72mph. i said i would do it at 65 , but i will probably try 72. i put in 11.045 gal of 94 octane , i haven't done the math , but i think only with the 1/4 tank of 87octane i should still be above 91. about 200 miles at 72mph and 75 miles of whatever.very few stops including signs and lights , coffee/mothernature , 5 deliveries , 1 warmup. maybe i will count them, yes , i am very bored. i'll guess 23.

calgaryhhr

I've come across this a number of times on my road trips throughout the states. It's a real PITA. The first time I had this happen I thought about entering my postal code but the pad on the pump only had numbers so I knew that wasn't going to work. I then entered a random 5 digit number, of course that didn't work. I asked the guy on the other side of the pump if he knew what the zip code of this area was and he looked puzzled. I then told him I was trying to use my Canadian credit card at the pump and it wanted a zip code, I realized I wasn't going to "beat the system." I had to go inside the store to pre-pay the pump using my credit card.

Canuck

No it's an interesting system in the US, using a credit card they (only some station) then request (at the pump) your ZIP code to validate the ownership of the card. Can't enter a postal code, it only accepts numbers on the key pad (i.e pin numbers, etc.), Neat process but frustrating for us foreigners.

Canuck

I disagree, determining the most economical fuel to burn is very valid, I never said I attributed the results to the quality of the fuel, nor am I trying to evaluate the quality of the fuel, just the mpg and $pm in my SS. Knock itself isn't a problem as there is reactively no acceleration involved, no real inertia to overcome just steady state cruising.

BTW -- one tank of 91 gave me 30.3mpg best fuel, best number to-date, but only the one tank, too early to come to any conclusion and haven't computed the dollar per mile involved but interesting.

Canuck

I was surprised too, but the math (sorry to bring that into the discussion) supports it. 3mpg is a 12% improvement while regular to premium is less than a 9% increase in cost (the few stations that I checked the numbers at), results in a net savings, if you run premium and if the results are correct.


Back on the road now and almost a week in Phoenix (tomorrow), mix of city/highway driving so next update wouldn't happen for a little while.

mistermike

Certainly determining the most economical fuel is valid. However if knock retard is involved, this introduces an additional variable that invalidates the results purely attributable to fuel. If you monitor KR and / or octane scaler, you will be shocked at how easy it is to initiate. You don't have to be vigorously accelerating. Just keeping a stead speed up a mild grade can be enough to trigger KR, depending on the particulars of the engine.