Fox My stock 91 GT performs better on 87 gas

MrPerfect2

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All stock engine - 327 gears and X pipe - after trying many brands and many octanes from 93 to 87 , car seems to idle better , more responsive and has better power running on 87 .
 
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Mustang5L5

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That's because it should.

Lower octane ignites easier and has a more complete burn. The only reason to run higher octane is when a tune or power adder creates a situation where you would get detonation with 87 octane. In that case, the higher octanes would be needed due to their nature of resistance to preignition.

But a stock 5.0 Mustang? Run 87 octane if you can.

The whole regular vs premium thing is marketing 101. Call it premium and mark the price up slightly and people will think it's better and want it.
 

MrPerfect2

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So , cars with turbos and high compression engines need the higher octane to resist pre-detonation ? Along with manually advanced timing adjusted cars ?
 

jrichker

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Engines with high mileage and carbon buildup will often require 93 octane for ping free performance with 14° advanced base timing.
The better grades of premium gasoline have fuel system additives to help reduce deposits in the liquid part of the fuel system along with additives to reduce deposits on the intake valves and intake ports.
 

MrPerfect2

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When you say “ better grades of premium gas have fuel additives “ are you saying the 87 gas has no cleaning additives in them ? I also heard the generic companies just buy gas from the major refinery companies - I also heard that all gas starts as 87 and they add the octane additive to cause it to be less volatile and bring octane ratings to 93 . Another aspect is that all octane grades share the same hose at the pump , meaning if guy who bought 87 before you then you get about a good bit of the 87 that is sitting in hose . Btw , I am not really that OCD about this topic , just simply chatting on subject - who really know what’s in those mystery underground tanks at the pump , lol .
 

Noobz347

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When you say “ better grades of premium gas have fuel additives “ are you saying the 87 gas has no cleaning additives in them ? I also heard the generic companies just buy gas from the major refinery companies - I also heard that all gas starts as 87 and they add the octane additive to cause it to be less volatile and bring octane ratings to 93 . Another aspect is that all octane grades share the same hose at the pump , meaning if guy who bought 87 before you then you get about a good bit of the 87 that is sitting in hose . Btw , I am not really that OCD about this topic , just simply chatting on subject - who really know what’s in those mystery underground tanks at the pump , lol .

Plenty of people do and you can too depending on how interested you are on the topic.

All gas at the pumps in the US contain burning and performance and cleaning additives. Pump fuel with a rating of 89 or higher has essentially the same additive package as 87 with even more additives to increase octane and an altered detergent package more suitable to higher compression burning.

It is a misnomer that lower octane gas ignites easier than higher octane gas. That is only true of ignition by compression and not true of ignition by spark.

The "flash point" of unleaded doesn't change very much because of the additive package although you can find exceptions; Mostly in winter additive packages in colder climates.

Non DOT rated gas is different altogether including things like Sunoco race gas.
 

Mustang5L5

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Gas all comes from the same refineries really. There aren't that many people making this stuff given the cost of such an operation. Depending on the middleman, certain additives get added to the fuel such as detergents. These are added across the board to all octane levels at a certain brand and the only difference is the octane level.

There are also many other variables that come into play when determining what octane level to run. The general rule is to run as low of an octane as you can run without experiencing detonation. Higher octane allows you to be a little more "aggressive" with compression ratio, boost, or tune because the fuel actually resists burning, but that resistance can also cost power, which is made up by the advanced boost, timing, or CR. It's a chicken and the egg really.

I've always wanted to see a dyno of a N/A car tuned conservatively to run on 87 octane, and then flush it and run 93 octane. My guess if the car with 87 octane would make slightly more power.
 

Sparky714

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When you say “ better grades of premium gas have fuel additives “ are you saying the 87 gas has no cleaning additives in them ? I also heard the generic companies just buy gas from the major refinery companies
I worked in a truck loadout facility in SoCal years back and every brand in the area loaded at the same facility. They just added their specific additives at the rack. I currently work at a refinery with their own loadout that does the same thing. Their is one set of stations in the area that don't, but they have their own refineries. So for the most part, all gas at the pump is the same, just with brand specific additives.
 

90sickfox

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My brother drove for Carluzzo and Baltimore Tank Lines delivering fuel to Maryland gas stations. Most of them get fuel from one or the other. Cosco and Wawa use the same gas from the same truck. He told me that the law states that the fuel from the pump must be at or above the posted rating. He then told me he only carried 89 and high test. Stated that a bunch of pumps that state 87 are actually 89. 89 is the best seller at the pumps...so the trucks carry enough to keep with demand.
 
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