Hey guys, I just added a custum exhaust "dump" right before the pipe goes into the muffler. I have noticed that I get a little bit of "backfire" noise when I let off the gas sometimes. Also, the engine does not "rev down" when I let off the gas, only when I push in the clutch. Is this normal? Do I need to do any mods to O2 sensors or anything like that. I would really appreciate some input.

 

as far as i can tell it's normal it is just the way your car reacts to low back pressure

 

I think it's perfectly normal, my duals do the same thing