Tuned pipe length

[scottyray]

I need some help I have a FSR-OX 30cc boat, which advertises it has a tuned Pipe. I did a centerline measurement from the exhaust port to the Fatest part of the cone and it measure 16 inches. From reading on forms I know 13 1/2 is optimal, red wire in picture. it has a 7/8 dia header. The only problem is is I can’t make it any shorter. It seems to run well but I’ve never had it in the water yet, the next question I have is, if it runs good in the water ,the header length that extends in past the second O-ring, right now extends 2 inches past the 2nd oring . should I cut that at a 1/2 after the second O-ring ? Here is a picture the red wire is at 13 1/2 inches long.