Glass Packs

Buddy had Cherry bomb 'truck muffs' (glasspacks) right off the headers of his Cleveland under a 71 Mustang. They have a 3-4 bolt flange that bolted right up wo the collector. about 30 inches long total and then nothing....loud as F. Could hear him getting on it from a block away. They were not terrible on the road, just very 'droney' and it got to you or you just blocked it out Depending on how long you were riding in it. I have an old pair of 3" Spintechs that look just like shoe boxes with spiral weld marks. Supposed to 'extinguish the sound waves' or some BS. All I know is they seem to work and they were $20 a piece used at a swap meet.