Well I rode it again with the dB killer in and had my brother listed from the roadside. He said it didn't sound loud enough for him lol. He also didn't like the slightly tinny/metallic sound with the dB killer. He much preferred the sound of the muffler without dB killer but it's too loud for me. So i turned up an aluminium (7075) addition to the dB killer. 50mm long. This adds some mass to the dB killer and eliminates the raspy/tinny sound and also reduced the overall sound level. Sounds cleaner. I like it a lot now. Not sure if the added back pressure will affect Hp or Torque at all but I didn't notice yet. Will try back to back when i get the chance.