Gas Choice?

[RVA CJ]

What gas do you all put in your rigs? I have a I6 AMC 258 i6 / 4.2l stock motor. Is it worth putting in the high octane stuff or is the low grade stuff just the same?

 

[rufus1138]

quick fuel theory, octane rating is an anti-detonation expression, so if you can get away with lower octane fuel without having to retard the timing excessively then you will get better power, response, and mileage. more octane rating without an increase in compression or induction manifold pressure is a waste of time and money.

 

[starcommtrey1]

One word. STABIL.

 

[starcommtrey1]

quick fuel theory, octane rating is an anti-detonation expression, so if you can get away with lower octane fuel without having to retard the timing excessively then you will get better power, response, and mileage. more octane rating without an increase in compression or induction manifold pressure is a waste of time and money.

To add to this food for thought, diesel has more potential energy than gasoline and a much lower octane rating which is why they get better mpg's and torque.

 

[RVA CJ]

So....fuel stabiliser and 87 octane fuel?!?!? I'm blue-collar, so I think that's what y'all are saying.


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[Old Dog]

I'm going the other direction here and going to say that everything I own runs better, and gets better gas millage on 93 than it does on 87.

 

[rufus1138]

To add to this food for thought, diesel has more potential energy than gasoline and a much lower octane rating which is why they get better mpg's and torque.

actually this opens up a whole new can of worms, diesel isnt applicable to octane rating, the rating for what is similar to anti-detonation ratings in diesel fuel is called cetane instead of octane and has nothing to do with its potential energy, the potential energy of relative fuels is their btu per pound factor, in relation to this diesel has a much higher energy density than gasoline, alcohol or nitro-methanol. of the 4 fuels i mentioned the odd comparison comes from diesels that make lots of torque and pretty good power, regular pump gas vehicles that make decent hp and torque then you have alcohol racing engines that make very good power and lastly nitro-methanol engines that top the charts with ridiculous numbers. the reason alcohol and nitro-methanol are so effective in internal combustion engines is a factor not of energy density (in which alcohol/nitro-methanol are far inferior to gasoline even, much less diesel) but of flame propagation rate, the fire burns much more quickly in the cylinder with alcohol/nitro and as such you can build an engine that will turn more rpm and can pack in more fuel for the same parcel of air giving you more power without having the fuel still be burning when the exhaust valve opens. this is why diesels may be made to make very good power numbers but wont turn the same ridiculous rpms needed for racing.

 

[RVA CJ]

actually this opens up a whole new can of worms, diesel isnt applicable to octane rating, the rating for what is similar to anti-detonation ratings in diesel fuel is called cetane instead of octane and has nothing to do with its potential energy, the potential energy of relative fuels is their btu per pound factor, in relation to this diesel has a much higher energy density than gasoline, alcohol or nitro-methanol. of the 4 fuels i mentioned the odd comparison comes from diesels that make lots of torque and pretty good power, regular pump gas vehicles that make decent hp and torque then you have alcohol racing engines that make very good power and lastly nitro-methanol engines that top the charts with ridiculous numbers. the reason alcohol and nitro-methanol are so effective in internal combustion engines is a factor not of energy density (in which alcohol/nitro-methanol are far inferior to gasoline even, much less diesel) but of flame propagation rate, the fire burns much more quickly in the cylinder with alcohol/nitro and as such you can build an engine that will turn more rpm and can pack in more fuel for the same parcel of air giving you more power without having the fuel still be burning when the exhaust valve opens. this is why diesels may be made to make very good power numbers but wont turn the same ridiculous rpms needed for racing.

Haha, so you're saying "no" to 87 octane or was that a yes?


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[rufus1138]

I'm going the other direction here and going to say that everything I own runs better, and gets better gas millage on 93 than it does on 87.

you can make more power even if you advance the timing further with higher octane, however the gas mileage increase is unlikely to balance out the increased cost per gallon of the higher number fuel added with the risk of getting bad gas because less ppl pump from the high octane tank at the station meaning the gas is likely to be much older than what is in the cheap tanks.

 

[rufus1138]

Haha, so you're saying "no" to 87 octane or was that a yes?


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im saying yes to 87 octane, at the pump its statistically likely to be the freshest and theres nothing wrong with putting it in your jeep and adjusting the distributor timing to suit.

 

[RVA CJ]

Distributor timing? I'm afraid to ask, but how will I know if that's necessary?


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[RVA CJ]

BTW, this is great and please no one take offence! I'm blown away by the wealth of knowledge here!


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[DHugg]

I'm going the other direction here and going to say that everything I own runs better, and gets better gas millage on 93 than it does on 87.

Alcohol belongs in bottles, not gas tanks. My AMC 304 likes 89 alcohol-free.

 

[RVA CJ]

Alcohol free? How do you get that? All pumps in VA have ethanol


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[Old Dog]

im saying yes to 87 octane, nothing wrong with putting it in your jeep and adjusting the distributor timing to suit.

Distributor timing? I'm afraid to ask, but how will I know if that's necessary?

I guess I see no reason to de-tune the engine just to run cheaper gas.

You will know you need a higher octane or later timing if you get pinging while accelerating.

 

[RVA CJ]

I guess I see no reason to de-tune the engine just to run cheaper gas.

You will know you need a higher octane or later timing if you get pinging while accelerating.

That makes sense! Thank you! I will keep on, keeping on with the 93 octane then and add stabiliser. Thoughts on that Old Dog?


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[Old Dog]

That makes sense! Thank you! I will keep on, keeping on with the 93 octane then and add stabiliser. Thoughts on that Old Dog?


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I like to use 2 cycle oil with a TC-W3 rating, mixed 1 once to every 5 gallons of gas. I never have gas problems, even after sitting all winter.
It's also much cheaper than gas additives. The last gallon I bought was $12.

 

[RVA CJ]

What does the 2 cycle oil accomplish? Also, the TC-W3 rating? If you have a few minutes, I could use the education.


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[Old Dog]

my best answer is this link.http://www.jeep-cj.com/forums/f49/fuel-additives-2058/.

 

[starcommtrey1]

actually this opens up a whole new can of worms, diesel isnt applicable to octane rating, the rating for what is similar to anti-detonation ratings in diesel fuel is called cetane instead of octane and has nothing to do with its potential energy, the potential energy of relative fuels is their btu per pound factor, in relation to this diesel has a much higher energy density than gasoline, alcohol or nitro-methanol. of the 4 fuels i mentioned the odd comparison comes from diesels that make lots of torque and pretty good power, regular pump gas vehicles that make decent hp and torque then you have alcohol racing engines that make very good power and lastly nitro-methanol engines that top the charts with ridiculous numbers. the reason alcohol and nitro-methanol are so effective in internal combustion engines is a factor not of energy density (in which alcohol/nitro-methanol are far inferior to gasoline even, much less diesel) but of flame propagation rate, the fire burns much more quickly in the cylinder with alcohol/nitro and as such you can build an engine that will turn more rpm and can pack in more fuel for the same parcel of air giving you more power without having the fuel still be burning when the exhaust valve opens. this is why diesels may be made to make very good power numbers but wont turn the same ridiculous rpms needed for racing.

They can turn them just not cheaply. When they do, OMG. Rare and they blow easy, but I have seen a 6.0 powerstroke turning 8k RPMS. He was untouchable.

BTW and just FYI, I only run 93 octane because I cant get racing fuel for a cheap price. I got a hight compression motor. And the higher that is the less it likes low octane fuel....