Who says 91 octane is not needed?

[srimes]

Only way to tell would be a back to back DYNO with AFRs mapped out for us.

Right? Closed experiment in same conditions. Only change being fuel grade.

No, that isn't the only way. That would take the least number of test samples to draw a conclusion, but checking mileage the old fashion way works too. You just need more samples (several tanks of each in similar conditions) to weed out the noise.

 

[CommanderXJ]

My jeep hates the 87 octane gas here. I have tried seafoam, mopar combustion chamber cleaner, and gave it a full tune up but it just runs worse on 87 octane. It LOVES 91 octane and runs 1000x better on it and I get slightly better mpg on it as well.

I don't know if its the quality of the gas here but if the extra 3 bucks per tank is gonna take care of any spark knocking noise then I'll gladly do it.

 

[kf_chris]

I gotta echo the good stuff being just better. I got better milage regularly, with both the 4.0 and now the stroker with high octane fuel. I'm not going to do a bunch of tests when I know that I got more miles per tank and a little peppier performance. That being said. I don't need to run the pricey gas with the stroker. I can't keep my foot out of it most of the time so I'll burn the cheap gas.

 

[IslanderOffRoad]

Get us 6 accurate/calculated pump-to-pump samples before you decide to fork out for 91 octane. Your sample size is too small.

I stand by my recommendation and use of 87 octane for a stock 4.0 engine. Octane is simply an anti-knock index.

Don't believe me? GOOGLE it.

Agreed, there are far too many variables here.

 

[Apostle]

Can anyone confirm this?? I don't remember seeing anything but 87 in my manual

Have the 97 man. ill check it next time i go outside (its cold). since im going to be towing next week, will be good info if correct

 

[Raymont]

Ethanol is the reason for the difference in mileage......

The amount of energy released when 1oz of ethanol is burned is far FAR (not gonna get mega tehnical here, this forum has no EVO drivers I hope) less... than 1oz of gasoline....

E85 has an octane rating of 110. Lets say your car makes 200whp on E85

Now, you take your car and use 110 octane gasoline and make 200whp. You can do it with 40% less fuel. (less pulswidth of injectors, less fuel pressure, you get the point)
...........I know were not talking about e85, but you get my drift.


So if you put in 10 galons of 87 octane that was 10% ethanol, you'd have 1 galon of ethanol in your tank. That is where the mileage comes into play, ask ANYONE with flex fuel cars.... their MPG SUCKS

 

[88 Wagonman]

I had thread about this a while back: http://www.naxja.org/forum/showthread.php?t=962675

I agree that it SHOULD run the same on 87 but on my 88 (98 longblock, renix injection) it does get better mileage with the 91 than the 87. You asked that the OP of this thread do more samples, well I have been testing that theory since August 2008 and the results have always favored 91. As far as the ethanol argument, your right, but my fuel is always (87 or 91) 100% non-ethanol. I guess this is where the disclamer comes in: "Individual results may vary."

 

[winkosmosis]

Wouldn't the 91 octane have the most ethanol?

 

[88 Wagonman]

Wouldn't the 91 octane have the most ethanol?

I think it's percentage based, around here there is E-10 (10%) and E-85 (85%).

 

[jeeper98xj]

fyi say the person befor you pumped 87 into thier tank and you push the 91 button the first 5 or so gallons......... will be 87, or what ever the person befor you pumped. its been in the paper more then a few times here in the chi.

 

[96XJ_4.0]

fyi say the person befor you pumped 87 into thier tank and you push the 91 button the first 5 or so gallons......... will be 87, or what ever the person befor you pumped. its been in the paper more then a few times here in the chi.

Weights and Measures only allows a set volume of fuel to be trapped in the system, that way the octane grade you pay for is not diluted. Longer hoses would violate this and that is why all hoses are the same length, style, and grade now.


Ask me how I know?

Please ask...:laugh3:

 

[96XJ_4.0]

Please delete. Re-post

 

[winterbeater]

If you google this stuff (I did), you will find some (seeminly reputable) claims that regular gas actually has more thermal energy than premium, due to the anti-knock additives in premium to make it burn slower.

 

[bigalpha]

Weights and Measures only allows a set volume of fuel to be trapped in the system, that way the octane grade you pay for is not diluted. Longer hoses would violate this and that is why all hoses are the same length, style, and grade now.


Ask me how I know?

Please ask...:laugh3:

Here's how the system works:

There's either 2 or 3 underground storage tanks (USTs). Regular gasoline will generally be a larger tank than the others; 12k gallons vs 10k gallons. I think I may have a few pictures of tank removals.

If there are 3 tanks, one tank will have regular, one tank will have mid-grade and the last will have premium. When the gas station receives a fuel drop, there will be 3 different trucks.

More recently, they have started installing two tanks of equal size (12k gallons). One tank will have premium and one tank will have regular. In order to get the mid-grade, there is a blender at the dispenser that dispenses some of each and blends them together.

When you look in the parking lot, you can determine how many tanks are located there by looking for the covers to the sensor ports and turbine sumps. The turbine cover will be very large, almost 4' across. If you see 2 or 3 of those, you know there are 2 or 3 tanks.

Now, each tank is plumbed to each dispenser. So if there are 5 dispensers, there are 5 sets of underground piping for each tank. The turbine sumps (big lids in the parking lot) are basically big pumps that pressurize the piping and push the gasoline through the lines into your car. [Side note: slow dispensing is usually indicative of a clogged filter at the dispenser].

When you pump your regular gas, the dispenser switches which line is activated at the dispenser. So you pump your $50 worth of regular into your car then hang the nozzle back up. When the next guy comes to pump his premium, he hardly gets any of the regular. First off, the lines that supply the gasoline to the dispenser aren't very big. Second off, there's not a lot of line between the nozzle and the switch at the dispenser. I would be surprised if you got a gallon of product from the previous person.

Any questions?

Side note: Not all gasoline tanks have pressurized lines. Every commercial gas station will, but some places just have a smaller tank to fill up a tractor or a few trucks. Those types of systems are called European Suction because the dispenser sucks the fuel from the tank; there is not turbine that pushes it from the tank.

 

[B192734]

I've noticed over the past couple of years that if I fill with plus, then I tend to get about 40-50 extra miles out of a tank. I don't seem to get the same benefits when driving in the city, but out on the highway there's a definite difference in mileage.

 

[xxxjjj]

x2.
89 manual specs are 87 or higher, for knock reasons mostly (aki), it also specifies that excessive gasohol (90% gas 10% ethanol) have caused engine damage in tests.

 

[96XJ_4.0]

fyi say the person befor you pumped 87 into thier tank and you push the 91 button the first 5 or so gallons......... will be 87, or what ever the person befor you pumped. its been in the paper more then a few times here in the chi.

NOT AT ALL TRUE.

Here's how the system works:

There's either 2 or 3 underground storage tanks (USTs). Regular gasoline will generally be a larger tank than the others; 12k gallons vs 10k gallons. I think I may have a few pictures of tank removals.

If there are 3 tanks, one tank will have regular, one tank will have mid-grade and the last will have premium. When the gas station receives a fuel drop, there will be 3 different trucks.

More recently, they have started installing two tanks of equal size (12k gallons). One tank will have premium and one tank will have regular. In order to get the mid-grade, there is a blender at the dispenser that dispenses
some of each and blends them together.

When you look in the parking lot, you can determine how many tanks are located there by looking for the covers to the sensor ports and turbine sumps. The turbine cover will be very large, almost 4' across. If you see 2 or 3 of those, you know there are 2 or 3 tanks.

Now, each tank is plumbed to each dispenser. So if there are 5 dispensers, there are 5 sets of underground piping for each tank. The turbine sumps (big lids in the parking lot) are basically big pumps that pressurize the piping and push the gasoline through the lines into your car. [Side note: slow dispensing is usually indicative of a clogged filter at the dispenser].

When you pump your regular gas, the dispenser switches which line is activated at the dispenser. So you pump your $50 worth of regular into your car then hang the nozzle back up. When the next guy comes to pump his premium, he hardly gets any of the regular. First off, the lines that supply the gasoline to the dispenser aren't very big. Second off, there's not a lot of line between the nozzle and the switch at the dispenser. I would be surprised if you got a gallon of product from the previous person.

Any questions?


Side note: Not all gasoline tanks have pressurized lines.
Every commercial gas station will, but some places just have a smaller tank to fill up a tractor or a few trucks. Those types of systems are called European Suction because the dispenser sucks the fuel from the tank; there is not turbine that pushes it from the tank.

You should have asked me how I know...

My father worked for Healy for 35 years.

I know the actual phyaics behind the newer pumps as my father helped to design better pumps used today.


That said.


The input fitting at the end of a modern pump into the hose is 1/4 inch wide. ONLY 1/4 an inch! It is under extremely high pressure therefore it can pump gallons per minute out of a small diameter pipe.


The pump line is 8 foot itself and is primed from within the unit along roughly 15 feet of 1/4 inch High pressure line. This equates to less than 1/5 of a gallon available in the line.

Like I said. Weights and measures has a standard that companies like Healy have to conform to. Compaines that produce some of the only pump systems used wordwide.
EDIT:
Want some pics? I have pumps in my backyard

 

[joe_peters]

Young whipper-snappers!

Norwalk, Hancock, and Gulf service stations, 1961-1975 family business.

Excluding diesel, two tanks--one regular, one premium. Blend pumps--you could move the selector from straight regular to straight premium and about FIVE mixes between the two.

Old tech rules!

 

[tbburg]

Don't know about the rest of you, but around here, most of the pumps have a separate line/nozzle for each grade. Sunoco is about the only one that has a single nozzle, and multi-grade switch(5 grades)

 

[hubs97xj]

In the last few years, almost every station around here has upgraded to the 3-4 button, 1 hose dispensers. I also see no large covers for the tanker hookups- all I see around here are smaller (1' dia?) covers where they refill. And my mileage drops in the winter- ethanol, the winter mix, my driving, extended idle times, or some combination.

Interesting stuff there alpha, I'll have to pay a little more attention to the covers- normally I just hear the 'thunk CLANK' when I run over them.

96XJ, I think your corn bin exploded.