I have just change the exhaust from 2 1/2" press bent to a 2" mandrel system. I have gone from 104hp ATW to 94 ATW but during the dyno run the radiator split the bottom tank so we shut it down without making any changes. so hopefully I will be able to get a few HP back, but the way the power ramps up and holds 90 odd hp for longer and the earlier more linier torque is encouraging.