Borla 22-23 Chevrolet Silverado 1500 ZR2 & AT4X 6.2L CC SB 147.5in WB S-Type Cat-BackBorla 22 23 Chevrolet Silverado 1500 ZR2 & AT4X 6. 2L CC SB 147. 5in WB S Type Cat Back This system features the classic BORLA(r) S Type sound level and turn down tailpipes. It was designed specifically for the Silverado 1500 ZR2 and Sierra 1500 AT4X and delivers great sound without any drone. Replace the small muffler behind the primary muffler in the BORLA(r) "S Type" system with Polyphonic Harmonizer 60680 to attain the "ATAK(r)" sound level