You're asking about ITBs (Individual Throttle Bodies) such as this
The 20v comes with them stock, or you could use an adaptor to put the 20v ITBs on a 16v, or use custom ITBs or make your own even.. not many people on here use ITBs that I know of other than the 20v guys.. From what I understand, ITBs on a 16v doesnt give you all that much of a gain, if anything just better throttle responce and a little more top end at loss of some torque..
You'll find that on here most people opt for swaps or turbo setups when they want more power.. 20v, 4AGZE, 4AGTE, or 3SGTE are the main swaps I see on here.. not many people build NA engines on here, as it takes alot of money to get enough power out of an NA rather than just swapping in a GZE, 20v, or turbo setup..
Brando