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I bring this up whenever someone asks for an exhaust with a 'stock' sound. (You said 'velvety', so I'm guessing that is sort of what you meant.)
If there's anything like a consensus here, it's probably for the A1 Sidewinder - an extractor '4-into-2-into-1' design that gets great performance out of our engines for the price. But one drawback is it's a little loud under acceleration.
I left a little performance on the table and opted for a more 'classic' look and sound - a Vintage Speed all-stainless exhaust specifically made for VW-powered replica Speedsters. The pipes are pretty close to what stock 356 pipes looked like, but this isn't a tuned header system.
Here's what it looks and sounds like:
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