The only mufflers Magnaflow makes that aren't straight-through core are their "Turbo XL" mufflers, which use the same S-bend style of flowpath that all "turbo" style mufflers do.
http://www.magnaflow.com/02product/universalsatinxl.asp
Personally, I never use a muffler that I can't hold up and see daylight through the other end.
