They are the actuators for the butterfly valves in the mufflers - which have a pushrod that goes through the transom rings, red bits below:



Overall this setup's worked really well - I've tried:

• Full wet exhaust : reversion
• GGB slip in mufflers - dry. no real difference in noise
• GGB slip in mufflers - water at the tip & rubber flaps. Quiet - but lots of reversion
• GGB slip in mufflers - water at the tip & no flaps. Too loud and a bit too wet. Didn't quite get water in the headers, but the collector was wet.
• Full Dry - ear splitting at idle

This is the best so far. Later in the year I'll put a little more water in at the tip and see if that brings the noise down a bit more without reversion.

MadMat,

Those look exactly like my mufflers with the butterfly.
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I was thinking of putting flappers on them to arrest stern wake water coming in. My dry risers are very shallow, but come out high.

Do you have much stern wake impact your mufflers?

It's a single engine rig with aluminium headers & heads, so not too heavy at the stern, although by design I have made my exhausts come out in the standard bravo locations rather than up higher.

If you're interested, you can see some more details of the exhaust setup here : https://mattyorke.com/2023/07/12/arr...2023-upgrades/

I was looking at the mufflers the other day regarding flaps. I don't think they'll "just fit" - the nice rounded shape the mufflers have means they're likely to slide off, I think, although I might consider a bolt to hold the flaps on if it also helps reduce noise a bit more and I can get just enough water in to avoid burning the flaps and avoid reversion. I'll keep you posted if I give anything a go.

Matt, really nice attention to detail in both the project and the documenting.

I feel the more projects like this get documented and archived, the more interest and motivation there will be for young men and women to tackle these in the future, as well as current events.

My concept for the heavy concave tips for flaps....was to make up some stainless pipe pieces about an inch wide at the proper flapper width, and tig it to the muffler, wherever it contacted on the concave.

But I'll have to see how high mine end up riding. Also have very littls water coming out...have 2x weep holes 1/8"top and bottom.

Cams are the hyd BBC Merc 365 Mag. 224° single pattern .510" lift and 115.5 LSA or something like that. So pretty tame for reversion.
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Like your concept of a relief valve in the exhaust system to draw in air at low pressure pulses.
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A lot of reverion issues are solved with a simple dam at the bottom of the riser.

Curious what you use the trolling motor for ?
Trolling ? lol

What brand of Fuel Injection is that???--- looks very nice !!!

Thanks. It's a Hilborn mechanical injection manifold that I converted to EFI. More details here.

Madmat, so you were seeing reversion with the full wet Eikert exhaust?

What size engine and cam?

When I inquired about that exhaust, it was recommended I go dry to the tip with a HP 500 carb. But I also read others had HP 500's and saw no reversion with wet.

Thanks

I can’t remember the cam right now (am away from home). But the whole motor is a custom build, originally starting with a bulldog 540 (tall deck). It has a hydraulic roller cam, too.

The design intended to allow dry to the tips and my mk1 tips did this, with ggb inserts and rubber flaps. Like this, but with flaps:

That was definitely far too wet and the motor would bog down. It ran OK minus the rubber flaps as per this vid, but I was still getting water up to the collector, and a bit loud.

Since then, I’ve decided that I want the collector to be almost totally dry, so all variations since then have worked on that goal. Obviously having the collector damp isn’t catastrophic reversion, but it’s more than I want. But if I can have it quiet enough and dry at the collector, everyone’s a winner. It’s nearly there.

The EGR valve, combined with reducing water at the tip to be just enough for muffling and no more, seems to be the ticket.

I looked up the full specs of the cam I'm running:

And did a post with more details of the engine here.