Inboard exhaust configuration
 

I have to start with what a GREAT SITE this is and how much great info has been shared by its members. I have owned several boats over the years most of which I have modified, restored, overpowered etc and just beat till they broke. Of them all the SeaCraft is what I have gone back to as they stand out above a lot of others for there sea keeping abilities. I am currently in the middle or hopefully beyond the middle of a 23 SF resto project.
I would greatly appreciate any help or input to configure the exhaust system as there was nothing to go by as I bought a hull, trailer and some parts but no engine or transmission. I have what I believe to be the original muffler (two 4" inlets and one 4" outlet) but was wondering what it had as original for exhaust manifolds and the height of the risers. My plan was to go with center rise manifolds and spacers 3" or maybe 6". I have a 4" heat exchanger I believe to be original Volvo and was hoping to be able to cool the exhaust system with fresh water if possible. I have not been able to find a cooling diagram for this setup (1974) any help locating a source for one would be appreciated. Power is a 350 w/ a 71c B&W transmission.
Thx to all that reply.

Tanks
 

Hope this photo posts & helps......
I had a 74-or 75 cc inboard.
No longer own the boat

My boat originally had a 351 Ford engine & I later put a 350 MPI Marine Power engine in its place. No problems ever with water coming in the exhaust

Aldo thanks for the reply and picture. Do you know if there were 3" or 6" extensions between the manifolds and risers? Where did your boat end up?
still LI? Did you get the Regulator?

My exhaust setup on my inboard is identical to Aldo's setup. I probably have a 12 -14 inch total vertical drop from my exhaust elbow down to a crusader swivel that right angles into the hoses connected to the muffler intakes. Getting as much height here is important as the inboard boats exhaust is below water and actually pitches down towards the engine. Not an ideal exhaust setup from a engineering perspective but a natural consequence of putting an inboard motor in this hull.

I had 1.5" extension blocks in my previous motor and never had any issues. My new motor im running dry stack exhaust and with the center risers is quite high already and im not adding anything this time.

Another shot of the barr marine "dry stack"

I have to agree with you on the less than ideal engineering. Do you have any flaps or anything other than the exhaust guard on the transom? Did the muffler you installed have a drain plug on it. I was wondering about the water in it freezing over the winter.

Looking good! Is that a 350 or 383? are the ex manifolds fresh water cooled and the risers cooled with exit raw water? I thought about possibly going the dry stack as well but haven't decided on anything yet. Thanks for the pics..

Thanks its a 350 vortec, risers are saltwater and manifolds fresh.

Thanks Miles,

looking back at some of your posts makes me feel a lot better about my project. Thanks for the info. Do you have any performance numbers with the Vortec installed in the boat. GPH or MPH #s? I have the close to the same setup going in my project. What do you run for D & P on the prop?

I like the looks of the height on those dry joint risers in the pic as well. Have you run it with that setup. Why did you choose dry over the earlier style?

No extensions on mine- 351 Ford, or later 350 GM. Just the rubber flapper. Boat spent plenty of time at Montauk and seas from every direction.
New owner still on eastern Long Island. Good luck with your project.

Just waiting for the crane to come set the vortec in the boat hopefully in the next few days. Ran it in the garage today and it sounds really good. I am told that the main advantage of the dry stacks is that if there is a water leak it will leak to the outside of the manifold/riser joints and not to the exhaust like the old style do. Meaning water wont leak back into your cylinders and major or catastrophic damage. The best i can explain it and it makes sense to me and worth the extra money. So i dont have any numbers yet but the 260 hp previous motor i had i was cruise @20-22 knots @3200 rpm and 9.5 to 11 gph. Running a 16X14 wheel. Hoping i can achieve 25 knots at about the same rpms and fuel burn with the extra 60 hp but we will see lol.

Montauk, Block and beyond is where I am headed with the race & gut as back yard. Glad to hear some experience with local water coming at you from all angles. I feel better knowing that I will have a setup that will get me back to the dock under its own power without water backing up into the engine.

Seems reasonable to me. 60 extra HP should be noticeable and provide the increases that you are hoping to achieve. The Vortecs are defiantly more efficient than their predecessors. Agree on the dry stack theory as well especially with raw water cooled risers. Good luck and keep posted on the outcome.

Will do, thanks and good luck to you as well. Mines been undergoing a 2 year long overhaul and im now starting to get excited about getting her back in the water.