Just got some nice BBF Bassett twisties from german1. Changing from Nicson logs. What kind of power increase can I expect? Bassett website says 15%. That is considerable. True or not?
In all honesty, it totally depends on the rest of the setup. The only time you will see a substantial increase going to headers is if your combo really needs the extra breath-ability of the less restrictive pipes...
It would also depend whether or not muffles are used, if you need to muffle things down to where you are with the logs, it will be a wash...

I always recommend headers from a performance standpoint, it just depends on how the boat is used and set up...

GT