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I HAVE A 1967 BIG BLOCK 427/390HP 4 SPEED COMPLETELY STOCK EXCEPT WITH A HIGH OUTPUT CAM......THE CAR IS VERY QUICK. I AM ABLE TO GET AIRCRAFT FUEL WITH 104 LEADED OCTANE.....CAN I RUN IT STRAIGHT OR SHOULD I BE SAFE AND MIX IT 1/2 OR 3/4 WITH UNLEADED HIGH TEST PUMP FUEL.
ALSO HAVE A 67 SB 327/300 AUTO AND A 1970 454/390 BB....CAN I USE THE SAME IN THESE CARS TOO. THE 70 HAS A COMPRESSION OF 11.
Much will depend on the state of tune of your cars (how agressive is the timing set, how 'tricked' are engine internals, what is the current state of engine wear/realized compression) and your altitude and driving habits. At high altitude (I'm 1/2 mile above Denver), you can get away with a bunch simply because of the native oxygen density.
My '65 396 which is stock and my '71 SB which is built out to the earlier 350/350 11:1 formula run fine off stock pump premium with NO ADDITIVES. Both when rebuilt saw hardened valve seat/valve technology, so leading in the gas is not an issue. And, no 'tricks' have been played with aggressive cams and/or spark timing advance.
But, if I drive down toward sea level (below 1000 feet) I have to make sure I'm running SOLID high test pump premium (+94 R/M rating) or dump a boost additive into the tank to run without pre-ignition effects. The best way to find out is try! Listen carefully for 'ping' and if you think you detect pre-ignition, get an octane boost additive into the tank without delay.
As engine wear takes place, your realized compression will fall and even though your cars are on the boarder for needing better than pump fuel, they may perform A-OK without it due to their state of wear. So, there's not really a black/white answer to your question as there's too many variables and cars here. You simply have to try. But, you've got a stable of HP vehicles and if you're at/near sea level, you're near the edge....
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