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post #1 of 11 (permalink) Old 07-13-01, 09:25 AM
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cool Gasoline to use?

I live in California and have been using 87 Octane Regular unleaded. I have a 1965 Mustang Convertible, 289. Should I be using a higher Octane? The manual says to use 92 or higher, but that was in 1965 before Unleaded gas!

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post #2 of 11 (permalink) Old 07-13-01, 11:09 AM
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when i drove my '66 daily, i always used 91 premium.

before CA stopped selling leaded gasoline, i used 100 octane when i could find it, otherwise it was always 92-94 octane premium.

try using the 91 premium and an octane booster. i've heard that these products don't raise it significantly, but it couldn't hurt. i've also heard of some lead addtives for older cars as well. forgot the name of the product though.


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post #3 of 11 (permalink) Old 07-14-01, 04:10 AM
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The main thing to know is the lower octane gas burns hotter than higher octane leaded gas. This means it is a bit harder on the valves than leaded gas. It is important to ensure the engine stays cool and does not get overheated and does not ping excessively. Keep the cooling system in good shape, drive conservatively and if the car pings, use a higher octane fuel or additive. If the car stays cool, and does not ping on acceleration, or when climbing hills then you should have no problem.
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post #4 of 11 (permalink) Old 07-16-01, 08:15 AM
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cool Thanks

I will try the higer octane. Its not a daily driver, weekends and nice evenings. The family and I like to cruise the beach with the top down.

post #5 of 11 (permalink) Old 07-16-01, 07:31 PM
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I use 93 proof and VP C-5 additive. It's the only additive I have ever used that you know it when it gets to the carb. Probably not available in Calif. as it contains real lead.
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post #6 of 11 (permalink) Old 07-16-01, 11:21 PM
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You might want to read this before you pump up the octane. The higher the octane rating the more resistant the fuel is to igniting. Used primarely in the higher compression motors and when using blowers or N2O.
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post #7 of 11 (permalink) Old 07-17-01, 12:40 PM
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The 60's model Mustangs were designed around the 100 octane level of leaded gas. The lead is a form of lube for the valve seats. Because gas no longer has lead, your valves will eventually wear themselves into the seat. Unless you have hardened valve seats, you need lead in the fuel of the older motors. The plus side of the additive of lead is that it also picks up the octane.
Damn I hate being old enough to know this.
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post #8 of 11 (permalink) Old 07-17-01, 06:05 PM
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Generally everything said is true. From a practical standpoint however, it's easiest to run what they sell at the pump.

Is this going to hurt the engine? No, not unless it detonates (pings). Lower octane fuels are more volatile, hence they ignite easier hence detonation occurs at a lower compression, and lower heat level. In normal driving, this is the criteria for using gasoline in your car. Spending any more money doesn't buy any more horsepower. In fact, the reverse is true. Lower octane fuels potentially offer more horsepower since they have a higher thermal output. Engines are heat machines...they convert heat energy to mechanical energy. The hotter they get, the more horsepower they produce...problem is, this same heat is destructive to the engine's component parts.

Now if the engine is subject to routine hard acceleration, climbing steep hills, or alternately the cooling system is substandard (overbore engines using factory cooling system), then there is a reason for using higher octane. The hard driving will result in detonation unheard with potentially damaging results. In this case, an ounce of protection is worth a pound of cure. Thus, in situation buy additives and the highest octane you can.

When you get arount to rebuilding the heads, get hardened valve seats as this is a weak area that can be easily improved during the rebuild process. There is normally no reason to jump up and tear your engine down just to accomplish this...unless you drive hard and fast.
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post #9 of 11 (permalink) Old 07-29-01, 09:07 AM
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My rule of thumb that I always tell people is to set the timing and everything else up as you want it. Then put the lowest grade gas in that will not ping. The higher octane gas can be compressed more before it will preignition, hence why high compression engines need it. If your car will not ping with 89 gas the only thing you get out of 93 octane is spending more money.
post #10 of 11 (permalink) Old 08-01-01, 07:42 AM
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I used a lead additive CD-2 in my 68 302 for about 12 years, before I sold it. I drove it to work everyday in traffic and on the weekend for fun. It is not an octaine booster, but just adds the lead. I used regular unleaded 87 oct all that time. No problems with the valves.
Good Luck

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