Holley EFI GPS Speedometer 553 123 exhaust bungs By altering the relationship between 93356 FBHB By altering the relationship between the primary length and collector diameter and length it is possible to increase or decrease the torque and horsepower output at any specific R This American Thunder® exhaust system comes as a complete true dual Crossmember Back exhaust for your 1969 Chevrolet Camaro or Pontiac Firebird with V8 engine CNC machined billet aluminum bezels with anodized finish – Bezels are threaded for easy replacement Holley is pleased to announce the continuing evolution of its very successful analog style gauges with the release of new 3 3 8" and 4 1 2" speedometers and tachometers to complement our 2 1 16" gauge line