Many things affect the sound of an engine.
I have heard a LOT of engines, each one has a unique tone, a Ford 4.6 modular sounds different than a Chevy 350, etc.
The 3.3 will never sound like a V8 to a trained ear. You can get close though, the sound depends on several things. The longer the pipes, the deeper the sound if all other things are equal. The more displacement, the deeper the tone as well, that's why I say a V6 with 3.3L will never sound like an average Chevy 5.7L V8. The more displacement, the more gas flow in the exhaust if all other things are equal.
To get a louder sound, remove the resonator and use a single muffler on each bank of cylinders. Beware that this will shift the power band of your engine up and reduce torque, hence the reason I am not a fan of true duals on anything less than a 4.0L engine unless some sort of forced induction is used unless top end HP is of paramount importance (top speed in exchange for less take off).
The valve train also changes sound. Multi valve engines like the 2.7, 3.2 and 3.5L will have a more refined sound than OHV 2 valve engines like the 3.3. This difference that the valve train makes is why a Lamborghini sounds different (and in my opinion, better) than a Camaro. I LOVE the sound of an LS1 Camaro.... but I get a chill down my spine when an Italian supercar whizzes by at full tilt!
Lastly, the number of cylinders affect sound as well. A 5.0L V10 Lamborghini engine sounds WAY different than a 5.0L Ford engine. The Lambo has a multi valve head and 2 extra cylinders, so it sounds different. The exhaust is different, but even if they were the same, the two engines would still sound different due to the other reasons listed.
