If you prefer not to use an external save editor, there are two common "in-game" methods to access these parts:

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In Career mode, you get them by winning "Unique Performance Upgrade" markers after defeating Blacklist members. These are strictly one-time use per career save. Quick Race Use:

: A known issue exists where applying a Junkman Supercharger to the BMW M3 GTR via an editor can cause the game to crash. It is recommended to stick to 6 out of 7 Junkman parts for that specific car.

Need for Speed: Most Wanted Junkman parts are the highest tier of performance upgrades, exceeding the stats of standard "Ultimate" parts. Because these parts are normally limited to a few random "Unique Performance" markers won from defeating Blacklist racers, many players use a save editor or trainer to unlock them for all vehicles. The Role of Junkman Parts

Some editors let you input multipliers directly. For :

Need for Speed: Most Wanted Junkman parts are "unique" performance upgrades that provide a significant stat boost—roughly 10% for attributes like torque and grip—on top of existing Ultimate parts