the plenum which is only attached at the center to the lower plenum. You wouldn't want to crack or bend the plenum and there is enough vibration in the engine and the plenum is wide enough that it could likely fatigue the plenum and crack or bend.. There are boost control solenoids on those brackets, and on the driver's side there is also a solenoid for controlling the PRVR system (which is a joke and you should ditch that system and just run a hose from the plenum to the FPR).. Hope this helps..