customcam
This is going to be tough because anything under 94 decibels sounds defective.
Everything helps. A good cam, Exhaust, Compression, Fuel etc.
Try an electric exhaust dump. When you get inspected you can be whisper quiet. When you get, "Outback", you can open your dump and blow the side off Ayers Rock!!
Don't forget a good Cam!
(for your car, the other would also be fun)
I'll be watching the TV for news of your Car.
Have Fun.
tyoneal