I'm not sure about the technicalities of how this slot works to quieten the exhaust but the tip has been repeated several times. How did you decide on a 10 mm width? I usually base my choice of drill on which one closest to the size I want that is still sharp. Maybe I'll try it on my straight through Armours stainless to see if it takes just a little edge of it. In reply to Bill's goldie silencer comment, when I was 17 I had a BSA Gold Star and it did have a genuine silencer that twittered. Interestingly, having bought the book, by Power Into Precision by Alan Vessy, A record of d. Napier & Son, there is a quote on page 161 when talking about the Deltic 16 cylinder type 4s fitted in locomotives had a whistling exhaust note - "not too unlike a BSA DBD34 Goldstar motorcycle of the same period". (Sorry, half strayed on to another thread that I started about timing covers and Deltics. I'll give myself a good slap!)Not sure if you can see it from this photo, it's 10 mm wide x 100 mm long in the underside of the tailpipe.
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I've got a reverse cone mega that was on the Egli a couple of years ago. It's actually a straight through silencer with absorption packing and an empty reverse cone on the end. The Egli ran really well on it, but it made an awful twittering noise on low revs. I put a piece of exhaust pipe through the cone and that stopped it.I was hoping you would say, It now had a Tweet !, That would be nice ,
I had a Goldie once, You guessed it , It didn't have a Tweet, Begger .