550 exhaust valve/back pressure/engine torque question

[Mario149]

My understanding is that part of the reason the standard 550 mufflers have a valve is that at lower revs some back pressure from the exhaust system is required in order to increase engine torque (to complement opening at higher revs for increased power).

Does anyone have any idea (from say before and after dynos) how much low down torque one might lose by fixing the valve open or fitting an unvalved system?

Edited for speelung

Edited by Mario149 on Monday 25th August 07:58

[Magic919]

I'd have said noise regulations, not torque, would be the reason. I don't think you experience any loss.