- Designed to address the severe airflow distribution issue with the factory upper plenum - Direct bolt-on replacement for all 1986-1987 Buick Turbo Regals, as well as the 1989 20th Anniversary Turbo Trans Am - Compatible with either a stock 58mm throttle body, a ported stock 62mm throttle body, or an Accufab 65mm or 70mm throttle body - Inc