OP is confusing the deafening roar that a child hears with a stock cammed 340 and some aftermarket muffs, that the rest of us hear as a low rumble with occasional loudiness, and is allowing the fog of childhood to skew what he's trying to recreate. Little kid ears hear a lot more than even young adult ears, and all ears will hear more than OP's, shortly.
But if OP insists on competing to be the stupidest, gayest, loudest a-hole on the planet, my decade in Harley/moto world makes this my time to shine:
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Please note: There are no women in this photo. Not even in the distant background.
OP, you want a diverging cone. Even the short-bus sheet metal shop can whip this right out if you don't have a Harley shop with a Parts Unlimited account nearby. Attach anywhere along your unmuffled system, and it'll get you what you want: All the attention your parents never gave you.
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Still not loud enough? Well, it's probably YOU not being able to hear anymore, but just make the big end bigger and/or the long part longer. The slash cut on the end will direct the noise. I recommend straight down if they're at the back of the car and you want to reflect the *ahem* noise off the pavement and then out to your admiring throngs, or you can orient them up to direct noise into the cabin if this exercise is simply because the world revolves around you, and that's where you'll be sitting.
