Butyl tapes are great for killing panel resonance. There is a lot of panel resonance in this car, so this is helpful.

There is a lot written on the subject of sound dampening / damping / deadening but these are helpful:
https://www.sounddeadenershowdown.com/products
https://knowledge.sonicelectronix.co...mpening-guide/

Exclusively using butyl sheets tapes may not the optimal strategy. Butyl to limit fiberglass panel resonance but use a foam/vinyl combo on top to really block sound. The factory carpet foam with rubber top in the firewall area was on the right track. I rebuilt the "foam triangle" between the fusepanel / ECU tray with carpet pad & dense rubber mat - this matched the height of the original piece. Then installed some closed-cell foam / mass load vinyl along the firewall and the engine noise is noticeably reduced. I'll be pulling the old carpet pad from under the seats and replacing with MLV/CCF, too, so see if further reductions in wind/road noise are possible.