The numbers that were in the 1978 HO Racing cat page 22 HO crossfire high performance muffler system. “The best factory dual exhaust for the 1970-77 Firebird is the 455 SD system. However, this system is still quite restrictive at high rpm. Drag strip tests indicate that a stock 455 SD will lose 80-90 hp through the exhaust system compared to one with open headers.”
“HO tests indicate a 30 hp gain compared to the 455 SD system with virtually no increase in noise. “ That is with the HR-93 1973-74 SD exhaust.
|