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I was wondering what type of fuel can be run in the old 289. I currently run premium unleaded, 91 oct. I was told i cant run unleaded fuel in this car until i change to hardend seats. Well ive been running unleaded fuel like this for 9 years now. The original manual states to run 94+ oct. That was stated when there was lead. I dont A) have 94 oct or B) leaded gas at the regular pump stations.

There are two stations in town that do sell a specialty 100 low lead and a 107 low lead premium fuel. Should i be running that type of fuel because it has lead in it? WOuld the extra oct damage the engine in anyway?

I have run this stuff in my 4.6L GT mustang but only mixed a gal or two in with the rest. (what a kick in the pants). But never knew if it did any damage or will do any damage to the engine.

Anyone runnig oct higher then 91?
 

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Hello danielf,
I would not worry about the gas too much. I plan to put my Mach 1 (351C) on the road soon and plan to run high test.
I plan to occasionally add lead additive to the gas. Perhaps every few tanks.
This additive is available at parts stores like "Auto Zone".
As far as the seats, I agree we will need hardened seats someday but I don't think we need to jump to it. If/when I develop motor trouble requiring the heads to come off, I'll change the valves etc. For now enjoy the car, do what you have been doing and perhaps add some lead periodically.
In my opinion the higher octane won't hurt the motor but I think it would be throwing away money. 289's are a healthy motor and if you keep the oil changed they go for lots and lots of miles.

Just an opinion from an old back-yard mechanic......Print Dad
 

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Do a forum search on octane, there are several threads already out there.

Unless you are buying your gas on the Mexican side of the border there is NO gas in the US sold for highway use that can contain lead. Its a federal law and has been that way for many years. The additives you buy can't have any of it either unless they are restricted for race track usage.

Too much octane will not hurt an engine. Too little can cause damage. However, if you engine runs well on 91 octane, more octane is not better and super high octane provides no advantage, it just costs more.

The octane on a US pump is an average of 2 measurement methods. In the 60s only the higher number was used. A 60s 94 octane is really about an 89 the way the pumps are now labeled, i.e. regular. If your 289 is close to stock I doubt it needs anything higher than pump 91. Unless you have the high compression 289 it probably can run on regular 89.

Octane and valve seat damage are two different things. Lead was use for both purposes. High octane unleaded works just as well as leaded except it doesn't protect valve seats. Valve seat damage is something that happens gradually and if the engine isn't working really hard, like a 289 in normal use, it may take a long time for you to see any problem.

Most premium gas in the US is used by people in cars that don't need it. It makes them somehow feel better but their cars could care less.
 
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