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Old 11-17-2010, 03:48 AM
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During the winter air is colder and denser therefor more fuel can be injected in the combustion chamber to burn. However the AFRs can be a bit more lean per unit of oxygen due to the lower temperature so overall fuel economy should be roughly identical.

Winter gas has a higher Reid Vapor Pressure (52psi) due to an increased amount of cheaper Butane. This is allowed because the cold air prevents an over abundance of vapor buildup in the gas tank. Low Butane blends during the summer have only a 6-7psi RVP. The addition of other more expensive chemicals used to replace the Butane increase the price of Summer gas.

The Seasonal gas program is designed to reduce evaporative emissions and will not affect fuel mileage or overall power. Any change in fuel consumption will be due more to temperature and air/fuel mixture variations between seasons.
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Old 11-17-2010, 05:22 AM
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Originally Posted by crater View Post
Please explain, using facts, why using higher octane than necessary/recommended on a stock car is the thing to do?

Its like saying you HAVE to use 93.. there are states (California being the biggest one) that don't even have 93, so clearly you don't need to use it. If a car only recommends 89 use 89 unless you've done something to cause it to need higher, or you datalog and see timing being pulled.
i grabbed an honest .2 in the quater and 3 mph from 87 to 93 octane... on the stock tune
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Old 11-17-2010, 02:38 PM
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Originally Posted by desertsoldier22 View Post
During the winter air is colder and denser therefor more fuel can be injected in the combustion chamber to burn. However the AFRs can be a bit more lean per unit of oxygen due to the lower temperature so overall fuel economy should be roughly identical.

Winter gas has a higher Reid Vapor Pressure (52psi) due to an increased amount of cheaper Butane. This is allowed because the cold air prevents an over abundance of vapor buildup in the gas tank. Low Butane blends during the summer have only a 6-7psi RVP. The addition of other more expensive chemicals used to replace the Butane increase the price of Summer gas.

The Seasonal gas program is designed to reduce evaporative emissions and will not affect fuel mileage or overall power. Any change in fuel consumption will be due more to temperature and air/fuel mixture variations between seasons.
Where were these "facts" pulled from?
The first 2 paragraphs may well be true but the third one I don't buy.
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Old 11-17-2010, 05:48 PM
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Originally Posted by waumo View Post
Where were these "facts" pulled from?
EPA.gov and just about any site related to refining gasoline.
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Old 11-17-2010, 06:36 PM
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sounds like a lot of cheap old dudes with fast cars that putt around, if you drive your car like it was build to drive you better put the best fuel in it to get the best performence from it. if you putt putt from car show to garage then you can run the cheapest crap you can find.
I bought my ride to drive like speed racer it never see's less than Sunoco 93 and only Sunoco93, unless i'm racing then she gets the VP109
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Old 11-17-2010, 07:12 PM
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Originally Posted by SRT5939 View Post
sounds like a lot of cheap old dudes with fast cars that putt around, if you drive your car like it was build to drive you better put the best fuel in it to get the best performence from it. if you putt putt from car show to garage then you can run the cheapest crap you can find.
I bought my ride to drive like speed racer it never see's less than Sunoco 93 and only Sunoco93, unless i'm racing then she gets the VP109
High octane gasoline is not "better" gasoline. It simply is more knock resistant due to the fact it is a slower burning fuel. Zero octane gas would be 100% heptane which is fast burning and explosive. However 93 octane is 93% Iso-octane 7% heptane. Fuels that exceed the knock resistance of a 100% octane mix are rated with a scale 100 or more. Fuel does not need to contain ISO-Octane in order to be high on the RON scale, Octane knock resistance is used as a baseline.

High octane fuels are more expensive not because they are better, but because they are more expensive to make and in higher demand. We have ingrained in our minds the marketing myth of "premium gas". Modern gasoline engines will adjust by following the knock sensor and dialing back timing or boost to compensate. Power loss between 91 octane and 87 octane in a Manual R/T is 4 hp and about .5 mpg. I have access to a dyno and have tested it during the summer. Unless you are running 2 year old gas with a Ron rating of 80 you should not experience knock in a stock tuned Challenger. This huge safety margin dialed in to the stock tune is what companies like Diablsport exploit when optimizing vehicles with more aggressive tunes. I woud not recommend running 87 octane with a DSPORT 93 Octane tune.

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Old 11-17-2010, 07:23 PM
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Its like this if you have a fast race horse would you not feed him the best oats you can buy him. Its like John said if you are going to putt around put in the cheap stuff. If you are going to run a HEMI engine like it wants to be run go with the good stuff. You will be able to tell a difference in performance. I have put 93 in mine since the first day I had it. BP or SHELL gas is all I have ever put in my car.
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Old 11-17-2010, 07:31 PM
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Originally Posted by desertsoldier22 View Post
Modern gasoline engines will adjust by following the knock sensor and dialing back timing or boost to compensate. Power loss between 91 octane and 87 octane in a Manual R/T is 4 hp and about .5 mpg. I have access to a dyno and have tested it during the summer. Unless you are running 2 year old gas with a Ron rating of 80 you should not experience knock in a stock tuned Challenger. This huge safety margin dialed in to the stock tune is what companies like Diablsport exploit when optimizing vehicles with more aggressive tunes. I woud not recommend running 87 octane with a DSPORT 93 Octane tune.
Well you must be lucky, my R/T 6 speed knocks (part throttle or WOT) even on 93 with the stock tune or otherwise.
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Old 11-17-2010, 08:26 PM
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winter mixes can have more ethonol too wich can hurt gas milage..
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Old 11-17-2010, 09:35 PM
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Originally Posted by Stricnine View Post
Well you must be lucky, my R/T 6 speed knocks (part throttle or WOT) even on 93 with the stock tune or otherwise.

That sounds like a serious problem! If you can audibly hear knock in a modern engine, it is way above the threshold necessary to trigger a Cel code for exceeding knock sensor voltage. If you can hear knock...your engine has already been damaged. With modern piston designed with thin ring lands, knock can utterly obliterate you internals. Are you sure you are not getting a misfire? Or hearing other noises?

Have you data logged your engine with a diagnostic tool?

There is no way a stock Challenger R/T will knock on 87 octane, the computer will not allow it. The car will go into limp home mode before destroying itself.
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