I've been wanting to build a muffler with a butterfly in it that allows straight thru when open and triple flow when shut. I kicked the idea round with a few mates an beers and this is the result. 3" straight thru or 1 3/4" triple flow. Seems to work alright, nice an quiet in "sneaky" mode, not that loud straight thru. Still makes good boost, but the microleb runs things a bit Ritch up top when in quiet mode.