I recently put on a Viper shorty slip on and noticed an extreme loss of power starting out in first gear. Also in low rpms in other gears. The Viper can I bought was a straight through can so probably next to zero backpressure.

After emailing a buddy of mine who had just installed a Scorpion Street Extreme slip on I found out that he didn't have the same problem as I had. Same bike but no lag down low.

I ordered a Scorpion and when it came in I noticed that it came stock with a decibel killer inside. I installed it and went for a ride. POWER! TORQUE! DRIVEABILITY! It solved my problem completely.
I then took out the decibel killer and went for a ride. NO POWER DOWN LOW! My bike needs the backpressure that the killer provided.

I loved the sound of the Viper straight through and the Scorpion without the killer in it but I'd rather have power.....

I have now found out that I can purchase separately a killer for the Viper. But, I like how the Scorpion looks and how it fits so I think I'll keep it and sell the Viper. I really liked the Viper's carbon end cap. Too bad I can't switch it out!