A BHAF Muffler  - Uhh??   I like the Cummins engine, but I try to do anything I can to make the engine quieter.  The BHAF air filter flows lots of air, but it also allows a lot of engine air intake noise to be heard in the cab – more noise than the factory air box and the factory air filter.   This inspired the idea to experiment with a BHAF muffler on a big honkin’ air filter –  in this case, a NAPA 2790. A BHAF muffler is not for everybody.  If you like air intake sounds, turbo