what are they and what kind of power do they make compared to long and short tube headers?

 

they make better "flow" than shorties so they are better for high reving engings with a lot a flow ex. v8 7500rpm redlineshorties have more back pressure and more torquey engins use then like a v8 4500 rpm redline
more flow does not mean less restriction is better it (unless the engine is boosted) i.e turbo, supercharger means the exaust has smooth flow throught the entire system