what kind of muffler is this?

It is definitely not a Flowmaster.I was a welder for Flowmaster for 5 years all Flowmasters have there name an them either embossed on the case or on some race mufflers have a tag embossed on a small plate and welded on the outside. They also have the style of muffler and the inlet-outlet configuration code engraved on the end cap of the muffler, plus that looks to be a coppy of there 40 series and the weld patern does not look the same.