1975 gpx mufflers

[1977srxmike]

Anyone have the bulletin or info on spec. On drilling the cone on the muffler. What will this do for the performance on it drilling the cones?

 

[338gpx]

here the best i could find from some old downloads

 

[338gpx]

found a clearer picture

 

[1977srxmike]

Thanks, Do you know what that did for performance ?