You said Thunder model. You might look at the AVS air door and tweak it a bit before you start changing internal parts.
The stock setting on the AVS air door is one and a half turns tight from where the door just barely closes.* The maximum setting is one full turn tight past that, or two and a half turns from gently closed.* Increasing the amount of tension will allow for a smoother transition, but it will start to hurt your acceleration at some point.* Decreasing tension will improve throttle response, but it will introduce a hesitation under hard acceleration if you go too far.*
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