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I'll admit my ignorance first thing. But based on what I've read, I define "Stage 1" as replacement of the H-D air cleaner element with a freeer flowing unit (Screamin' Eagle, Ness, etc.), replacement of the restrictive exhaust pipes with a freeer flowing exhaust, and carb. jet adjustments to handle the new air cleaner and exhaust.
I think it's sort of an unofficial definition.
But Stage 2 could include a hotter cam and maybe a replacement carb.
Stage 3 could include after market heads. And for a twin cam, stage 3 may include going to 95 cu. in.
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