new mufflers...opinion please
Beatnik, they tuned them to work well with little and big engines. The smaller engines with single exhaust or larger engines with duals typically get the lighter spring. The large engines and ones with lots of airflow get the stiffer spring.
The stiffer spring obviously keeps the valve closed longer so the sound level at low air flow (low speeds and small throttle openings) stays low and by nature of their internal tuning, the resonation is basically non-existent.
tom