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I come from carburetor land, where it's always been said that using 89 or 91 octane gas in a car designed to run on 87 has absolutely no benefit. This makes sense since the only point of the higher octane was to keep the gas from detonating before the spark timing.

Is this no longer true in the age of fuel injection, knock sensors, etc? Is there now a benefit to using higher octane even though the car runs fine on lower octane? Or are people still just going on the false premise of "more is better"?
 

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I come from carburetor land, where it's always been said that using 89 or 91 octane gas in a car designed to run on 87 has absolutely no benefit. This makes sense since the only point of the higher octane was to keep the gas from detonating before the spark timing.

Is this no longer true in the age of fuel injection, knock sensors, etc? Is there now a benefit to using higher octane even though the car runs fine on lower octane? Or are people still just going on the false premise of "more is better"?
Do not use higher octane levels unless the vehicle is tuned for it. You will see no gains and just be throwing away your money.
 

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Same is true. If the engineers optimized the car to run on 87 octane, then running 89 has no benefit. If the car was optimized to run on 89 and you put 87 in it the computer will sense detonation and pull back the timing, making the car run a little sluggish.

Custom tunes can take advantage of the anti-knocking characteristics of higher octane fuel to run more aggressive timing, giving you more power.
 

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In theory the car will calculate its current running conditions and if you have 93 in the tank it MAY advance the timing a bit. It won’t be night and day or maybe even not noticeable.

Ever forget, octane does not make more power. It allows you to make more HP, be it by more timing, more compression, etc. If you put 115 octane race fuel in a pump gas motor with no other changes you will most likely loose hp. Higher octane fuels burn slower than low octane fuels. You want to run the minimum octane without causing damage. That point will be where you will make the most power.

The only fuel out there that “Makes” horsepower is the heavily Oxygenated race fuels. Its about $20/gal at its cheapest. The Oxygenated stuff is worth a 5-7hp increase though. I use it in my bikes when racing and you can most certainly feel the extra punch.

Here is a link to VP's site. It may provide you with more information:
VP RACING FUELS- UNLEADED FUELS

I use MR9 in my bikes
 

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The "Spanish Oak" computer found in the 05+ is very powerful. It will recognize the higher octane after a couple of tank fulls. It will advance the timing etc to take advantage of the better gas. From what I've read and what Ford techs have told me, you might pick up 3 to 5 horsepower at the flywheel (depends on octane, altitude, etc).

You need to reprogram the computer (American Muscle sells SCT tuner products) to take full advantage of the available octane. A custom tune for your car from a reputable, experienced shop is the best way to go.
 

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The 2010 Mustang GT, and the 2008 and later Bullitts have upgraded computer programming which increases low-midrange torque approx. 10 lb-ft when switching from 87 octane to 93 octane.
 

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The 2010 Mustang GT, and the 2008 and later Bullitts have upgraded computer programming which increases low-midrange torque approx. 10 lb-ft when switching from 87 octane to 93 octane.
I knew the Bullitt did that, but I wasn't positive if the 2010 GT would or not.
 

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higher octane allows for 2 things in the tuning that can give you more power, with any engine. It just so happens, these are the ONLY 2 factors in tuning that can increase power.
1) Advance the spark timing. The further you advance the spark, the more power you get. (in our engines, about 4-5 hp per degree of timing). 25 degrees total advance in a 4.6 is about the limit, for bigger engines you can go to 28 or even 30 degrees advance, but in the 4.6, you start to lose power after 25 degrees. The downside is the further you advance the timing, the higher chance of detonation. If the knock sensors detect detonation (knocks or pings, etc) it will pull timing until it stops, then ease it back up to where it is programmed. The computer in our cars can pull up to 25 degrees of timing in effort to eliminate detonation, but it will always try to bring it back up to the programmed level. This is why if you have a 93 octane tune, you don't want to use 87 octane fuel.. you will have nothing but problems.

2) AF ratio. The air fuel ratio determines how well the fuel burns. When you advance timing, you get more time to burn the gas before the exhaust valve opens, but if you go with more air in the fuel, the fuel will burn faster (and hotter). The "optimal" air fuel ratio is about 12.5:1, BUT, the higher the AF ratio, the hotter the explosion, and more heat means more detonations. If you put race gas in your NA car, you could easily run 12.5:1 AF ratio at Wide Open Throttle and not have a problem, but with pump gas, just like running 25 degrees of spark, it is dangerous, and if the engine sees a ping or knock, it will pull timing in effort to prevent it, defeating the purpose of tweaking the spark and AF in the first place. The bad effects of a high AF ratio become multiplied when you add compression ratio or boost.

Newer computers, (as mentioned the 08 bullit and '10 GT's) have programming that will attempt to advance spark and lean out the fuel ratio slightly in effort to get more power, and if 91 or 93 octane fuel is in the tank, it will not detonate and you get a benefit (more power). If 87 or 85 octane is in the tank, the computer will pull timing and AF and you will be back to a normal "safe" tune. If you don't have one of these vehicles, you get no benefit from the higher octane fuel.

One way to look at octane is the "inability" for fuel to burn.. the higher the octane, the harder it is to burn.
 

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I have a stock GT engine and from my experience in this nasty hot and very humid Florida weather the higher octane gas helps. It is not something out of this world ,but the car runs better on 93 now that is summer. In the winter, I ran 89 and 93 and didn't notice the diference.
 

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I have a question when switching to the higher octane. I know you should let your tank get pretty low before changing. Do you have to adjust the tune at the gas station or can I drive it home and then put in my tune? Also, if I have the 91 tune is it ok to put in 93 gas? Will it hurt the car or will it run funny?
 

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higher octane will never hurt the engine, so you can get it near empty, fill up on 93, then go home and install the tune.. You actually want to run it for a bit to get the old gas out of the fuel line, which might take a few miles..
 

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I have a question when switching to the higher octane. I know you should let your tank get pretty low before changing. Do you have to adjust the tune at the gas station or can I drive it home and then put in my tune? Also, if I have the 91 tune is it ok to put in 93 gas? Will it hurt the car or will it run funny?
You can change tunes whenever you want, but I would drive at least a few miles before changing tunes to make sure you are getting the higher octane gas into your engine.
There is nothing wrong with using a higher octane than the tune is made for, you just aren't going to see any performance gains (just don't use a lower octane than it is tuned for).
 

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what octane to run

If anyone has any idea plaz tell me I bought my first mustang its a 02 gt its got no cats new intake manifold new intake k&n intake system flowmasters new pullys and whatever else it had done my question is I ran 93 and 87 for two weeks and I'm getting almost a 4 mpg increase when running 93 octane and it doesnt have no lights on the dash so I am assuming someone tuned the computer is this the case or what could that dramatic diffrence in gas millawge and power be thx for any help oh is it bad to run 87 I'm driving shorter distance to work now and my gas mileage running 87 has dropped from 18 mpg tto 14 but I'm also running ac and driving 2 miles back and forth to work a day now should it increase mpg to go to 93
 
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