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Stupid question of the day - gas
So, I'm new to the 71 mustangs, and the 351 in mine. I bought mine 4 months ago, drove it in on the gas that was in the tank, and immediately took it apart. Have never bought gas for it.

Now I'm asking myself, what kind of gas should I run in it (once it's back together)?
You should be able to run 89 octane but it will love you for buying higher octane!

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1971 Mach 1 - 306cid/C4 Bright Yellow
"Just relax, I've got a friend named Felix who can fix anything!" ~James Bond
regular gas is fine, you do not need lead additive.
From everything everyone has told me, pump gas should be fine. Higher compression engines may need additives, but if you don't hear detonation (pinging) while you are driving/accelerating, you should be fine.

I'm far from an expert, just info I've gleaned from this site and others.


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My 71 likes the higher octane.Runs a lot better..

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Go for the premium stuff the higher octane you can get at the pumps. Your engine will love you for it. It will be more responsive and will run smother. With the same timing Mine would ping with regular but not with premium. We have 94 octane at the pumps here But only through one gas company anywhere else is 92. With the money you will put in the car what are a few extra cents per gallon. {I am Canadian so I am used to liter's hahaha. So if it is a dollar more per gallon I plead not guilty for lack of knowledgeBig Grin}

hope this helps.


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basically if you have 87,89,93 octane go for the 93, if you have 95 or 97 even better.

the engine will run better with higher octane due to engine ping/detonation.

more octane also means you could add more timing until ping/detonation for more power.

the higher the octane the less chance the gas will pre-ignite. (higher flash point)

so lets say your running 89 and the engine is on the edge of detonation/ping that means some of the fuel is igniting Slightly before it should, that may translate into the feeling that your engine timing is retarded. retarded timing means more engine heat and less power.
when you drop 93 octane in the tank the fuel will ignite later or at the correct time which would feel like more power to your foot.

now you could run octane booster, this would allow you to greatly advance the timing without engine detonation.

when ever you saw old car movies like 2 lane blacktop right before a race you may notice them messing with the engine timing, and idle rpms. They would advance the timing all the way till the engine was on the ragged edge of detonation and bump up the idle rpms this was to get all the power off the line they could. then when the race was over they would reduce the timing back and the idle rpms to make the car easier to drive on the street and in traffic.

for our cars they don't need lead additive or octane booster , but they will run better on higher octane gas, but you don't have to use it if you don't want to, you can usually adjust the vacuum advance down or up for bad or good gas.
I run 91 octane( thats premium where i live) and it seems to run better than 87. I use shell gas, they have it real cheap next to my work!
oohh ya..even my low compression 1973 mach 351 4v will ping with anything less that 92..it loves 92 and above.
The 4 barrel carb version of the 1971 351C had 10.7 compression from the factory, so it definatly needed premium gas. My 351-4v runs fine on 91.
If your engine is old, there maybe carbon build up on the pistons, so even a low compression engine may need premium. The only way to tell without opening the engine is to see if it pings on a lower grade of gas.

Also it may ping if your timing is set too far advanced.

1971 Mach1
C6 is history-->>now TKO-500
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