As part of my fuel system upgrade I went with a 58mm BBK throttle body. While a 58mm holds the promises of more horsepower over a 48 or 52mm model, it is not without some difficulty. In my case I didn't do my research like I should have, so I will have to pull the intake off to open up the throttle bores in front of the intake. It's not a major problem, but it is something to be aware of if you decide to upgrade your throttle body. If you look inside the bores it's clear where the bore creates a step in the airflow.