Dogdays, 17748s are center outlets so that is likely what you run too. I have some spares around.

And as Eric said, the three pass mufflers are pretty similar. For reference, the old true Corvair Turbo 2.5" inlet/outlet muffler flows about 54% of an open pipe. The SuperTurbos, around 70% or so, UltraFlos around 100% and typical DeltaFlow Flowmaster-type mufflers around 53% or so, depending upon inlet/outlet configuration and length.

The patented flow directors do add a lot to the air flow potential through the three pass SuperTurbo mufflers even if the pass tube diameters are slightly smaller than inlet and outlet bushings.

The old stock mufflers are in the range of 35% or so. My VOE is about 33% then switches up to about 55% or so. Not super hot-rod performance but better than some others you can buy and I have the option of running quieter than stock but as loud as chambered mufflers. :)

Tom Hand