Late A headers on an early A (smallblock)

65cudalover said

Reality is most small block motors do not need headers unless you are going over the top drag racing and high end horsepower. I had my 66 prior to its being run into by a fool, running 12 second quarter mile on well fitting and slightly worked normal exhaust, just set up as dual pipes that had good flowing mufflers. Its all in the motor not whats going out.

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I do agree with some of this but not all. I good set of cast iron logs worked over will be more than enough for your 318 with little mods to the engine. Now if your talking about a 340 on up with a decent cam, intake, bigger carb, lightly worked over heads then your going to need some sort of header.

Remember most engines from the factory are choked up at the intake and exhaust for low rpm performance that's ideal for a factory street performance car. When you add a bigger carb and intake, your trying to cram more air into an engine that can't exhale well because of the factory exhaust. Now you'll need to add headers and a larger exhaust pipe to allow the engine to exhale the extra air your trying to make the engine breathe in.