Im looking at replacing a set of leaky manifolds that cost an engine with a used set that was a through hull setup on a different boat. Through hull isn't an option as I want to keep my stock formula quiet thunder swim platform so I will need to take like 7 inches off the ends of the set of used tails. Would I just be able to tack the inner wall to the outer at the end to keep the inner tube in place? (leaving enough room to let water out of course) On my current setup the inner pipe is flared to meet the outer right at the tip with two holes in inner at 12:00 to let the water out. The used set is also flared but its more of a star pattern(like crimp), where the negative space between the "points" let the water out. ill try and get pics. I called the manufacture of the used set and they said they can't recommend shortening the tails, because the inner tube may crack. (which I'm not really worried about being at the end). Won’t let me post pics yet.

You might want to cap the bottom half of the jacket, and let water only flow out of the top half. This sort of dumps the water into the exhaust gas flow and the pulses "blow" it backwards and splash the inside of the remaining exhaust instead of just running at the bottom of the pipe. Like in this picture. This is the how stock risers and aftermarket risers meant for through-prop or silent choice/captains call are usually made (that I've seen).
An easy way to do this is like speedy said, and use 1/4" round bar (or whatever size fits in the jacket), it can be bent with the same radius as the inner pipe and tacked in.

Thats kind of what I had in mind. I just didn't know if this would be sufficient, rather than screwing around with a pipe expander and trying to make holes in just the inner.

I know for Dry Joint manifolds they have different gaskets to make water come out the top a lot and not much out the bottom. one end of the gasket has a pee hole and the other has a larger diameter hole. I would think you could make something like this for regular risers but I am not well versed on regular risers.

https://www.wholesalemarine.com/gask...xoC4v4QAvD_BwE

And for the record the guy in the video in that link put the top gasket on backwards..lol..

Chris

Not really. Restrictor hole faces forward on dry joint systems. Purpose is to stop cold water from entering manifolds through the hose going to the riser. Once stat opens up water is fed to manifolds through lower hose.