Some organizations allow you to move up in classes (ECTA) but SCTA doesn't if that is who you are referring to.
Personally I support it as now you have people competing on a more or less even playing field having to set records with engines that are available in that displacement range. In some displacement classes you might be able to find a smaller engine that is more highly refined. In blown classes, especially with turbos/intercoolers smaller engines might be able to dominate classes of larger displacement, especially in special construction where frontal area comes into play since they can fit in a vehicle with a smaller frontal area.
Cases can be made for allowing it but SCTA doesn't so those are the rules if you are racing for a SCTA record,
Sumner