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Would it make a difference if I used the 97 Octane rather than the cheapest 87 Octane? And would it be worth it to get the better gas?

Just Curious...

Zach
 

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Cheapest gas is the best.

If you use a higher octane and your car doesn't require it you're just polluting more. Plus your car will build a dependency for the higher octane. 87 and Fuel injector cleaner once in awhile is A-OK.
 

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Discussion Starter #3
Ahh, thanks. I've been wondering about that.

Zach
 

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All Fords are tuned to run 87 octane stock. However you can get a little more performance and milage running higher octane in SHO's. The ECU in the SHO advances the timing until it hears knock then backs off a little for maximum performance, hence the "premium recommended" on the gas guage. Of course if you have a chip or LPM you may have to run premium; my LPM equipped SHO runs poorly with less than 91 octane and really bogs down on 87. I found my SHO runs best with 91 octane with octane booster since my LPM is tuned with premium on the dynojet. I have added 5 gals. 100 octane Unocal to a tank full of 91 octane a few times.

Bob
 

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Just use the 87 octane stuff.

The BTU content of a gallon of 87 and 93 is the same. Octane is a measurement of the ability of the gasoline to resist pre-detonation. As a car gets older, carbon tends to build up on the pistons and cylinder head. Carbon is a great insulator and will cause local hot spots to develop. This is usually at the edges so gasoline there will detonate before the spark from the spark plugs detonate the main charge. You then have two separate explosions happening at the same time and when their shock waves meet, you get engine knock and a loss of power.

If you run higher octane and your car doesn't need it, it's just a waste of money. Cars with knock sensors can retard the timing but that may affect gas milage and power.

In my last car, it seemed as if it needed it more in the summer than the winter, but that was when it had about 80k+ on it.
 

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Originally posted by LineNoise@Sep 27 2004, 05:30 PM
Cheapest gas is the best.

If you use a higher octane and your car doesn't require it you're just polluting more.  Plus your car will build a dependency for the higher octane.  87 and Fuel injector cleaner once in awhile is A-OK.
Umm, no.

the octane rating has no bearing on pollution.

The car can't "learn" octane ratings and gain a dependency for it. If you have a vulcan without a knock sensor that advances or retards timing, the car won't even be able to notice or adapt to the higher octane fuel.


I have a chip in mine that requires that I use 91 octane. It needs it because the timing is advanced enough that it needs the slower flame point of 91 octane fuel.


The rule is, the higher the octane, the slower the fuel will burn. But yes, there is the same thermal amount of energy in 87 as 91 octane fuel.

And cheapest gas is not always the best. There are alot of different conditioners and additives that are in gasoline, and the additives are manufacturer specific. "Premium" fuel generally has chemicals in it that clean out carbon build-up and the manufacturers actually recommend that if you use premium fuel don't use any fuel additives. They can detrimentally react with the additives already in the fuel and harm your engine.
 

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One thing to think about is where you buy your gas as well. I know that a lot of places in the states have older pumps and tanks. Be care not to get too cheap of a gas and end up paying more in the long run. Just my $.02 worth.
 

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The only vehicles that need higher than 89 octane are those that have a compression ratio of 9.8:1 or higher. Even then, some of the newer vehicles with compression that high do NOT need higher than 89 octane. Technology advances on...

If you NEED higher than 89 octane to prevent detonation, there are other problems that need to be resolved, the higher octane is only helping you work around combustion problems, and you are paying more for nothing.

Most notably is carbon buildup. This is the #1 problem that causes older vehicles to knock.

#2 is a mistreated coolant system. Improper functioning thermostat and air in the system causes the cylinders to be hotter than normal. Deposits on the cylinder wall insulate the cylinders and cause the same. So does a slow flowing waterpump (corroded fins).

#3 is low oil pressure. The oil helps cool the block, heads, pistons and cylinder walls. As oil pressure drops with age due to worn bearings, the oil flowing through the motor is reduced as well. This is more important for motors that spray the pistons via an oil path through the rod than those dependant solely upon oil spray from the crank itself. Those that spray the piston directly usually do so specifically to remove additional heat from the piston.

Put simply, heat in the cylinder is the enemy, and you want to reduce it as much as possible to get as much power as possible out of the motor.

Also of note is the fact that as knock sensors age, some of them begin to produce "false positives", that is, they indicate a knock condition when the source of the noise is not actually a pre-ignition event. A loose cam gap, or even a well worn motor support can set some of them off.

Have you ever replaced your spark plugs? Did you install one of the fancy platinum wire or split-fire or whatever plugs? All plugs are not made equal, and even though the plug may be in the mfg's list as being available for use in your engine, it may not be what your engine needs. Pull the plugs and check them to see if they functioning properly. If they appear to be running too hot, they can be a pre-ignition source. If they are running too cold, they will cause too many misfire events, which leads to a buildup of carbon, which leads to pre-ignition.

Do you have one of those eBay horsepower kits that fool the PCM into thinking the engine is cold all the time? If so, remove it. It causes your PCM to provide a rich fuel mixture all the time, and this will lead to carbon build-up, which leads to pre-ignition. They also cause your cats to go bye-bye at a young age.

Are your O2's in good order? They can cause a rich or lean condition in the cylinder.

Did you remove your 1 7/8" exhaust and put on 3" pipes without doing any other mods to take advantage of the pipes, like a 30psi turbo? If so, put the original pipes back on. You have actually lost a ton of power, and too much exhaust is remaining in the cylinder, causing the combustion cycle to be extremely cool, which leads to carbon build-up, which leads to pre-ignition, at least when you eventually put a proper exhaust back on the car.
 

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I always get the cheapest! It will not make that much of a diff. Usually the gas stations around me have 3 levels and the bottom two are always the same price so I put in the middle! When I went on vaction this summer I found gas stations that had the highest octane the cheapest so I got a couple takes of that in!
 
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I unno about you guys, but I use 89 Oct. 92 Octane when I get the Chip fron Alberto...


Sal
 

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shell v power is the best i've used in a while. i have a crazy program in the eectuner that requires high test other wise i get part throttle knock. Peace_Corey
 

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91 all the way for my SHO and the absolutly cheapest for me beater... what a pos.
 

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I tried Shell V power for two tanks and had a drop in mileage of about 2 mpg (yes, I track almost every fill up on my iPaq). Back to Thornton's 87 for me.
 

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I used to use Mobil 87 octane, but after I tore apart the UIM to change the plugsand found loads of carbon, my gf's dad recommended shooting three or four tanks of 93 octane through, then dropping down to 89 octane. The premium has better detergents in it, which will help clean the carbon out. Eventually, I'm going to rip off the UIM and LIM and clean them out completely, but I didn't have time that day...

I'm now on my last tank of 93 octane, and when I fill up next week, it'll be back to 89 octane.

JR
 

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I think it'd be good to be careful when people say "cheapest is best," where people use the word "cheapest" to mean regular/87 octane. If your car was designed for 87 octane, use 87 octane. If your car's manual says 91 octane like my LS did, then use 91 octane. Some have done mods to their engines (chips, etc.) requiring higher octane, and that's fine. But the fact of the matter is that 87 is perfectly fine for most stock, ordinary cars and trucks.

As for detergents found in fuels, within a brand of fuel, the detergents are the same in 87/regular as they are in 91/premium. The only difference is the octane (see HenrySEL's explanation of octane).

The oil companies got into a lot of trouble a few years back over their advertising which focused on the detergent and performance qualities of their "premium" fuels and lead ignorant consumers to purchase premium thinking that it would make their cars perform and clean fuel systems better than using regular, which is simply not true...
 

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The absolutely cheapest gas (like from the club warehouses and no-name brand places) aren't usually the best. I heard they add water to their gas.

And gas on the west coast is oxygenated. They add ethanol to the gas to reduce the amount of carbon monoxide. This leads to lower gas mileage and higher prices, but less people are being poisoned by CO. I think it's gov't BS. True CO can kill you, but I haven't heard of people dying from it just by breathing city air. I heard that Shell adds the most to their gas.
 

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I certainly wouldn't go to some bargain gas outlet either. I'd just buy the regular/87 at Shell, Exxon, Sheetz, Sunoco or someplace like that...

Part of the reason gas is sold at the price that it is is because not only does the government require oxygenated fuels in some places, but there are different formulations of gas to meet the hodgepodge of emissions requirements across the country, over a dozen formulations in fact. Which means the limited number of refineries that this country has are stuck producing a whole slew of gasoline formulations which drives up the cost.

And just think about the oxygenated fuels...If you use oxygenated fuel, and it decreases your gas mileage, obviously, your engine isn't running as efficiently and you're having to use MORE gasoline, so how environmentally friendly is that?
 

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Ture, ethanol will lower the gas mileage, but they say the number of people still living because of lower CO makes up for it. BS! It's population control! Just plant more trees!
 
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