cam, cam, cam
oh, and heads
but mostly cam
did i say cam?
seriously
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bore it out between 30 and 40 over, find the perfect cam,
then find the right heads and then on to rockers and springs and intake manifold and headers, and high performance aluminum water pump, high volume oil pan, high volume oil pump, high volume oil filter, here's where you buy a charger of ur choice if goin' all out, if not then on to picking a carb, two carbs if you wanna be then man and punch a hole in the hood, and air filter device of your choice, cold air is the only way, wether is above the hood or up in front, since ur buying a kit, find out if it's internally or externally balanced, if it's externally, you'll need a harmonic balancer for a 400, and the flywheel as well, then go all out and dress up the rest of the engine bay with high performance or high cosmetic.
and the rest is up to someone else