87 vs 93 debate

I do not want to really start an argument here, but after what merlin posted in another thread last week, I had to put his words to the test. I recorded the numbers and I will let you guys double check my math.

When I first filled my tank from near empty on the Cherokee, I filled it with 87 octane, regular fuel. I refueled and filled the tank after my tripper hit 253.6 miles. my needle was about quater to empty. It took 14.973 gallons of fuel. Now correct me if I am wrong, but when you devide the gallons into the miles you are left with 16.937 MPG. I am not up set with this number out of this motor.


Now, JUST to prove merlin wrong, when i refilled the tank I filled it with 93 octane, premium fuel. Then I hit the tripper and went about my business. My route never changed, NOR does my driving habbits. It is a mixture of free-way AND city, just like the first tank. I swear under oath this is true. At 251.4 miles, I refueled it again. It took a full 13.685 gallons of fuel. Now doing the same math again, I reached a total of 18.370 MPG.

On both tanks, my A/C was run intermitently and I do play with this 4.0l...... I always use my cruise on the free-way set to 70mph. I travel the same route to and from work, every day. These tanks were as close a match as I could get them. I can do it again and take pictures of the actual meter readings if you do not believe me. But like I mentioned, premium fuel burns more efficient, AND improves mileage.

now did I save any money? YES. It was about 6.62 cents per mile on regular based on what I paid at 2.56 per gallon, and 6.21 cents per mile on premium based on 2.96 per gallon. So NOT ONLY did I average better mileage by about 1.5 mpg, I also saved close to a half a penny a mile! I hate to be the guy who takes the time out of his life to prove a point like this, and again, I am not trying to start an argument, really I am not..... but since I have actual proof and numbers to work with, I had to post it up here.

Do the math yourselves and see, I am not making this up. these numbers are 100% true based on the instruments I used. And math cannot lie. Premium fuel does increase efficency and can save you money! Now wether or not you want to run this fuel is completely up to you. I am not pushing that anyone should, so please do not miss-understand me. I just wanted to prove my point.

im not saying your wrong but im not saying roberto is wrong eather.. you have a higher compresion motor so the premium fuel is an advantage to you and you will see your foot off the throttle a little more then with regular fuel.. if you had a 4 cylinder low compression jeep motor you would accually see it decrease your mpg.. they have less then 9.8 to 1 compression so regular fuel burns better.. i know this from doing doing computer tunes on peoples cars.. i always ask what type of fuel they usually buy so i know were to start.. for a turbo car you should never run anything else besides 91+ octane because of the higher compression under boost.. granted you will see more turbo lag under normal driving conditions because it will always run a little rich and not burn completely but thats just to keep it safe and prevent knock under quick acceleration and fast spool up of the turbo..

for a low compression motor like the old dodge 318s i tell them to run 87 if they dont have any internal work or cam in it.. they have a compression ratio of 8.6 to 1 i think.. 93 octane would do nothing but run the car pig rich and probley make it shoot flames.. lol.. for the newer 318s they are pretty similar but it isnt such a big deal because i can play alot with there computers.. lol..


basically what im tryin to get to is every car is different and every car or truck performs different.. i know alot about the newer computer controled vehicles and i know how to make them more effecient air pumps cause thats basically what they are.. all you really want is to get the most air in, get the best air/fuel ratio into the cylider (14 parts air to 1 part fuel) and then get the spend exhaust out of the motor as fast as possible.. there are so many variables between the weather and driving conditions that you cant say 93 is better then 87 in every motor... like i said.. in a high compression motor higher octane is great. in low compression motors 87 octane is ideal... but in colder weather 93 octane is alright in low compression motors because the air going in is more dense.. and this is based on stock vehicles.. if i hook my laptop up to an ecu the sky is the limit on what octane you wanna run.. i could make it so you can run alcohol or methenol on your daily driver and not blow it up with supporting fuel supply mods of course.. lol. this debate can keep going forever but that basically wraps it on with my knowledge on the subject..

oh yeah.. i also know how to make them run on water.. you need to highly modify your fuel setup to make it run off the hydrogen your seporationg form the water but who knows someday i might put one together just for shits and giggles.. see how fast i can make it run in the quarter mile.. lol..

Wow !!! That is very informative Joe. I didn't know that. My son keeps preaching how we should be using premium fuel in our Volvo to get ultimate performance and for it to run at peak efficiency.
I had no idea what he was talking about. Now you made cents of it all.

Tkx

You know what joe, that was very well said. But you know that I am now going to have to pick a different animal and try this again....lol.... Would you accept results from a 2006 Chevy Cobalt? and I will post them, wether they are good or bad.....




But excellent post though.

guess when im running on less then 3 hours of sleep in 48 hours things start to make sence coming out of my head.. still havent slept since i wrote that and let the partying continue.. i think i died today and went to heaven but ill leave that for my thread.. lol... when im all done with the ls1 swap ill do a stock ecu setup and then a modified ecu setup just to prove what i can do with a modern drivetrain.. in the firebird the car averaged about 23mpg with my tune and 4.11 gears.. the red truck is gonna have 3.73 gears and a different intake and ecu so ill be able to start from scratch minus the VATS system.. all im doing is there is taking the factory security system out of it though..

Tell ya wat tho. It really dont matter you pay more for 93 and less for 87. and still pay the same amount pretty much

Junior, no offense, but your 'experiment' proves nothing. You have no way of controling all the other variables, so everything else you do is going to effect fuel economy. On top of that, driving style alone plays a huge part in fuel economy. 1/2 a penny a mile? 1.5MPG? That could simply be how much you used the A/C.

A few things to note;

If you look at any gas pump, it says the number posted is the minimum octane listed. You very well could get '87' that is 93. So yet again, another variable that is very difficult to control.

The higher the octane, the lower the BTU (energy content) is. 87 octane is actually 6,000 btu's higher than 130 octane aviation gas.

The higher the octane, the more difficult it is to ignite. So it actually takes MORE energy to ignite the fuel.

Like Joe said above, and i've said before, if the vehicle isnt tuned for premium, it wont do anything but drain your wallet. But if your happier using premium, but all means, go right ahead.