Firstly the standard 2l black top throttle body has the same bore as the inlet manifold it bolts to so you cant go for a bigger bore throttle body as it will leave a step. The silver top inlet might be different bore size but I cant remember. The power boost valve is so you can have it set up properly to match any other mods. A guess yes that the st170 manifold flows better but i'm confident that it does. If it dont then thats no loss to me. The st170 manifold has the same port size and shape as the 1.8 and 2l silver top heads so no mods needed apart from the height. I dont know if the black top is different as I have not looked