necking down after collecter?

Treblig said

One muffler shop dude told me (and it made sense) that the exhaust is hot near the headers and cools as it travels out the back. That's why you can hold your hand over the rear exhaust pipe but not at the header outlet (too hot). Cooling gas should condense.....so the same amount of exhaust gas (volume) at the header should decrease in volume by the amount that it cools (temp) off as it travels to the rear.

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You're referring to what's called "tuned exhaust".... what you do.. is... you take shoe polish, and you wipe a fkn line every 8 inches from the collector on the extension.... or about 3 line...the last line of shoe polish that burns off.... is where you would attach the muffler....imo that has NOTHING to do with the diameter required...smaller would probably move that line further down the pipe even..'more heat'. Need to know what you're doing and not let some Ck biter steer you queer.