r/classicmustangs • u/Sleep-Senior • 2d ago

Which Fuel?

289 in a 64.5 and I do not know any specifics about the engine internally. It is a 65 block. 600cfm holley carb. I have raced with race built Chevy engines and this engine does not feel like anything special so I imagine mostly or all stock.

Been running 87 with lead substitute since I bought it. Timed based on that fuel.

Any noticeable gain to running higher octane?

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u/1320Fastback 2d ago

87 is fine and I doubt a lead substitute is needed unless you know for sure the engine has never been apart. I would though run Sta-bil 360 Marine every fill up.

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u/beejonez 2d ago

I'm running E0 fuel which is higher octane, 92 in my case. I don't know if the extra octane makes much a difference, but the lack of ethanol definitely does.

Edit: not everyone is lucky enough to have clear gas locally but I found my station using https://www.pure-gas.org/

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u/Sleep-Senior 2d ago

Is it the same as "rec gas"?

The place I get fuel for my boat pops up.

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u/beejonez 2d ago

Possibly? Mine looks like this...

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u/Tee-Bomber 2d ago

Yes, Rec Gas and E0 are the same thing. Ethanol kills small engines and deteriorates fuel lines and other components that were never meant to run Eth.

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u/Trick_Sector5900 2d ago

It depends on if, but more likely when the motor was rebuilt. Any motors, hi-po or stock that were built during the era of leaded gas definitely need a lead additive when running on today's gas. But when I restored an early '65 mustang I first located a '65 block that hadn't been bored over, then I took that to the machine shop, told them everything I was going to run on it, from carb to intake to exhaust, to trans , etc. and also that it would be able to run on today's gas.

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u/Random-carpet 1d ago

I run 93 and stabil marine. Engine has never been touched and runs great.

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u/MorganL57 1d ago

91 octane to mid grade. More common C-code 200 HP V8. Compression should be above 9. Make sure you have a good filter between the pump and the carb. More than likely there is ethanol in the fuel you are using.

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u/dale1320 5h ago

With today's computer controls you may hlget more horsepower from high intake fuel. BUT it won't be "seat-of-yhe-pants" noticeable. You might get a little more mpg, depending on driving habits. You would probably see a tenth or 2 of a second quicker at the drag strip.

You