[nmarlow]

have a 69 with a 351C. Which fuel is the best & do I need to add an additive?

[keg65]

69 was still running Regular lead gas.

If the heads have ever been rebuilt, they would have added the hardened valve seats. If so, run the lowest octane it will take.
These are of course easy to adjust timing to work with any fuel. If you get "pinging" with 89 octane, just back off the timing a bit.

I'm not sure about a lead additive for original heads, I'm sure someone else will chime in...

[bighoss88lx]

Originally Posted by keg65

69 was still running Regular lead gas.

If the heads have ever been rebuilt, they would have added the hardened valve seats. If so, run the lowest octane it will take.
These are of course easy to adjust timing to work with any fuel. If you get "pinging" with 89 octane, just back off the timing a bit.

I'm not sure about a lead additive for original heads, I'm sure someone else will chime in...

I was told since my old Ford truck still has the original valve seats that I should run 93 octane with the leaded fuel additive. Of course I did that until I started having a hard time finding the additive so I gave up and just run 87 octane with no ill effects so far.