A stepped exhaust collector or a cone shaped exhaust collector will both work, but each has its own benefits or drawbacks.
A stepped collector produces a greater acoustic signal, thus it is more effective, but only over a very narrow speed range. A conical (or megaphone) collector produces a lesser acoustic signal, so it is less effective at its peak, but it is also effective over a much wider speed range.
So take your pick, do you want flexibility or max power?
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