quad throttle bodies

theres this mod for NA engines thats been makin me wonder what it does. does it increase horsepower and torque? by how much?

it should increase horsepower because bigger throttle bodies feed more air into the engine and more air means more to combust. with a bigger throttle body i would also buy bigger fuel injectors to get the air-fuel mixture perfect.

It does depend on the rest of the engine and the design. If the restriction on air flow into the engine is the cylinder head, or exhaust, etc, then a bigger throttle body will not give any more power at all.
However, if you are going to modify the engine for more power, such as bigger cam or head work, headers etc, then a bigger throttle body will help power for sure.
On its own, there may or may not be any difference.

For high performance engines it's common to have separate throttles for each cylinders as this increase power somewhat and improve throttle response.

Normal road cars has often quite small throttles as the larger ones have more of an on/off feeling.