[TimBSmith]

Thank you Ed, Peter, Neil...

I went with the MMI wrap.

Now that I know the scale of schedule 80 black and SS I can redesign for either threaded common fittings or something welded. Either way I want better higher pressure flow than my street L and regular L provide at the top. I am going to be curious to see how much heat is produced there at sustained higher RPM. Also, I was surprised by the amount of backsplash at the injection point, corrosion traveled up the connector part way up the longer gap nipple. I suspect this produces back pressure on hot gases coming down off of the top of the riser.

ABYC. Since the mid 90's my boat has had 4 surveys. Assuming the past 4 owners have carried on the tradition of schedule 40 pipe, never once is this critical assembly mentioned in the surveyor's notes. Is this common? I don't care what the survey says, I care about running a reliable and safe boat, wonder how this assembly gets overlooked. The hull and deck routinely gets a tap/sounding test, maybe the hot exhaust should too. After what I experienced(and so many of you have shared) I know a lot more about signs and sounds of failure to look for.

Off to the boat to bolt my new hot exhaust in...can anyone advise on MMI flange bolt torque?

Grateful. Stay well. Tim