Perkins 6.354 Exhaust system replacement

[Enchanter]

Hi all,

We bought a Gulfstar 44' Motor sailer about 18 months ago and are working thru a refit. We have the non turbo 6.354 which is rated at 130HP. The Perkins is in working order and the exhaust system has been working fine but there are signs of seeping at the engine room bulkhead exhaust hose coupling which is at this point, loosely organized rust. The rest of the exhaust system is in pretty desparate shape as well.

I have done a lot of perusing of this forum as well as other good references and found some good recommendations. That said, I still have a few questions and would appreciate some sage advice on my plan.

I'll post some pictures and drawings to this thread after I submit as I haven't worked out how to do that at the same time. Here is a brief description and my questions. Pictures to follow.

For reference, the bottom of the engine manifold exhaust flange is about 5" above the water level. The existing riser is iron pipe, leading into a marine manifold wet elbow. From there it is a short 3" I.D. hose stub down into a stainless steel vetus lift muffler, top in, top out. The top of the lift muffler is at about water level.

The 3" I.D. hose on the exit side loops up about 19"and then thru a 45 degree coupling at the lower starboard engine room bulkhead. The coupling is apparently 3" on one side to 3-1/8" on the other. The hose run to the transom is 3-1/8" I.D. as is the transom fitting itself. The lenght from the aft engine room bulkhead to the transom exit is flat and ~11'. The transom exit is just above the waterline on the starboard side.

The Plan

1) I want to get a little more height in the riser portion. The top of the existing wet elbow is at about 16" above water level. I am planning to use black iron pipe into a new SS wet elbow from TAD which I have on order. One question I'd had was whether stainless pipe would be a better choice for longevity? I know it will be more expensive. Schedule 40 sufficient?

The new SS wet elbow has the water inlet on the downhill side which is not the case with the existing unit.

2) From what I have read here, I plan to use a Centek Vernalift muffler. Still working out the angles to determine if it can stay top in top out or needs to move to side angle in and top out.

The existing muffler seems undersized from a volume perspective. It is 9-1/2" tall and 8-1/2 in diameter. My thinking had been to use the 12" diameter, 12" tall Centek for added volume. The top of the existing muffler is at about water level so the new unit would end up a couple inches higher if I use the 12" tall unit. I can't get the muffler any lower in the boat. Centek also has a 10" tall unit - any theories as to what makes sense here.

3) I'd been planning on sticking with 3" I.D. hose as that is what is in at present. Centek's recommendations section says that for an engine our size we should be using 4.5" I.D. ports on the muffler which means replacing the transom fitting (we are presently in the water and getting hauled out isn't an option for the near term. Would appreciate perspective on that. On the one hand the system as currently laid out and sized has been working for th better part of 39 years, but that doesn't mean it can't be improved.

4) On the muffler exit side I was planning to get a little additional loop height but don't want to over do it. I have seen perspectives that seem to suggest get all the height you can and others that suggest a max of 4' above water level so looking for guidance there as well.

5) Lastly, I was going to try and use a straight coupling vs. a 45 in the run on the exit side. My question is whether I can get 3" I.D. hose to stretch over the 3-1/8" transom fitting and still keep my sense of humor.

I'll use stainless t-bolt hose clamps, 2 per throughout.

Pics to follow, thanks in advance for the perspectives.

[Enchanter]

Here are the accompanying pics. The first shows the existing riser, wet elbow and that small stainless can at the right is the vetus lift muffler. Notice it's size relative to the Onan genset muffler.

The first diagram shows the key components in the exhaust run. It is a top down view and roughly to scale. Top of the page is the forward engine room bulkhead.

The second diagram shows a rough elevation of different parts of the system relative to water level. It is looking aft on the engine room. Hopefully these help.