there is math for every engine.
it has never been correct for anybody...
compression ratio, 2 valve or four, deck clearance, type of headgasket, sedan or wagon side exit or not, single fire, double fire, spark volts, iron plugs or iridiums or platinums..wires, direct fan or electric, outaide intake air or under the hood..two row copper radiator or 1 row aluminum...
10% ethanol or nitromethane diesel...
a chamber calming the volume to your exact engine is the bassy rumble. have fun experimenting. and don't go open chambers, it is all a hoax. Even a lawnmower could sound badass and idiot with open chambers.