if you and i pace each other at 40mph for 1/8th of a mile, our turbos will no longer be spinning because they are no longer necessary to attain the speed we wanted. basically the turbo is helping the engine get to a speed faster than it could on its own. so once youve attained the speed, the turbo doesnt spool.
if you are going from a roll and pace without brake boosting, your turbo needs to spool basically from low psi. this is why its advantageous to brakeboost, because you are consistently spooling, and as soon as you let off the brake the turbo is already at 50-75% of its max psi.
i’m talking about both bb’ing from a stop and a roll btw