I doubt HALF. Some small losses, yes quite likely, but its only re-routing the exhaust gas, not blocking. Then again if you have it on fully closed your not going to miss a little power because your driving 'sedately', more likely to want power AND exhaust noise when fully open. Search 'Varex+aurion' on here & on Youtube...few videos up. No definite solution yet, but I imagine a high-flow cat, straight through mufflers would be a good start. More money means endless possibilities.