How much horsepower does a throttle body spacer add on to a 5.2L V 8?

It will add horsepower for sure , and you will feel the difference if your a good driver and know your car well . The increase depends on the engine situation and the car model too, on v8's it will usually increase from 5 to 20 hp and you can hit the 20 easily if you reprogrammed your computer , without reprogramming the gains will be from 5-15.