Reduce chamber pressure if engine turned off

[typer86]

Hi Hondata,
it is possible to reduce the pressure between plenum and combuston chamber if the engine is turned off?
I can hear a little, little sizzle noise between one of an injector after the trip - if the (hot) engine is turned off.

Air flow:
Throttle body > Rotrex S/C > intercooler > plenum chamber > engine

Thanks for any ideas.