Jeremy
.060 Over
It’s not as restrictive as it first appears, 140 or so hp can be made with it in place.
It acts as a resonance chamber becoming the large diameter change required to terminate pulse tuning. This is why swapping mufflers with everything else stock makes very little difference.
It’s also why when you replace it you’ll find a lot more bark in the exhaust, as the pulses are now running all the way till the end instead of reflecting from the box back up to the valve.
That does make sense @Claviger More bark would be nice. what is the correct way to eliminate it?