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I am putting a older opposed twin 18 HP engine in my Beck Boat....this is a direct prop shaft drive...these boats were Mfg`ed on Pine Island Fl in the 60`s -80`s for trolling ...slower the better ....my question is ...can I connect the 2 exhaust ports with galvanized pipe to a "T" and then straight up into a vertical pipe? I want to put a muffler just above the " T" fitting...then a aluminum up pipe that can be removed for going under low bridges. Since each cylinder fires alternately , will it cause any problems with getting rid of the exhaust? Thanks for any advice or thoughts ! Happy New Year !! David -Pine Island Fl.

Most of the old mowers with briggs and Kohler twins I have worked on the headers went into the same muffler, about ten inches of header from cylinder to muffler , I am attaching a link to a ebay page to better comunicate what I think you are asking, If I am off lets try again. Like to se a picture.:thumbsup:http://www.ebay.com/itm/Briggs-Stratton-Parts-Muffler-Manifold-Twin-L-Head-Ver-Horz-BS-Muffler-14-/361308870169?hash=item541fafd619:g:6NcAAOSwXeJYKr0a.

You didn't say what you are using for a engine . I take it that its a air cooled engine and not water cooled. All the air cooled engines that I have worked on the exhaust go's into one pipe and muffler. I have worked on some boat engines that are water cooled and they run water out the exhaust pipe for some reason.

Thank you RJ and Rey for your quick replies....yes it is a air cooled situation ....and I guess even though the set up I`m describing is similar to the stock design , I wonder if the stock muffler has baffles of some sort or partitions that would stop the exhaust from being pumped into the other cylinder-valves, causing carbon build up and problems down the road?......maybe over thinking this ....David

You didn't say what you are using for a engine . I take it that its a air cooled engine and not water cooled. All the air cooled engines that I have worked on the exhaust go's into one pipe and muffler. I have worked on some boat engines that are water cooled and they run water out the exhaust pipe for some reason.

As I said you don't say what engine you are using. If Its a 4 cycle engine its impossible for the exhaust to be drawn back through exhaust system into the cylinder. Just maybe a 2 cycle engine but never heard of it happing. In my snowmobile days they ran twin cylinder 2 cycle engines into a single exhaust system without any problem's , but they ran high RPM's. You said you are running this engine very slow so if it is a 2 cycle engine yes then can see problems down the road.

Martinomon said:

Thank you RJ and Rey for your quick replies....yes it is a air cooled situation ....and I guess even though the set up I`m describing is similar to the stock design , I wonder if the stock muffler has baffles of some sort or partitions that would stop the exhaust from being pumped into the other cylinder-valves, causing carbon build up and problems down the road?......maybe over thinking this ....David

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You might be over thinking it but in theory if you look at tuned exhaust I believe they talk about the length of each header pipe lenght to actually put a little vacuum on the next cylinder but I would guess the RPM's and displacement would all play into it. While talking about exhaust and over thinking it, on motorcycles when you remove the mufflers it is necessary to move up to two sizes bigger in the main jets to stop the back firing.
When checking valves on a engine with a vacuum gauge you watch for a steady vacuum and if it twitches it means a valve is not sealing so I would think any back pressure from another cylinder would show up on a vacuum gauge.

Reynoldston....sorry ....I don`t know how to use the forum yet ....this is a Briggs 18 HP Opposed Twin -80`s vintage...horizontal shaft 4 cycle........Rocky ...good info on the MC exhaust...I have 2 harleys and I know about the back firing....got mine right !....Thank you both for the info......I started messing with some pipe today and since the exhaust ports are off set , it will make it difficult to make an easy connection ...Question: is there a flexable metal(stainless steel) exhaust material out there that could be used to connect the 2 sides ...the size of the outside diameter of 3/4 gal. steel pipe? Or any suggestions ?? Thanks ~David

There is exhaust flex pipe. Easy to use but like everything easy there is a catch. Flex pipe won't hold up very long . 1 or 2 years maybe before it rust through. Take the motor to a exhaust repair shop . Have them bend some pipe for you .

Go to a auto parts store like NAPA and you will find they have adapter pipes that come in a lot of different sizes. Maybe a exhaust shop might help you out but I will bet not unless they do the whole job.

Good ideas ....thanks !

Martinomon said:

Reynoldston....sorry ....I don`t know how to use the forum yet ....this is a Briggs 18 HP Opposed Twin -80`s vintage...horizontal shaft 4 cycle........Rocky ...good info on the MC exhaust...I have 2 harleys and I know about the back firing....got mine right !....Thank you both for the info......I started messing with some pipe today and since the exhaust ports are off set , it will make it difficult to make an easy connection ...Question: is there a flexable metal(stainless steel) exhaust material out there that could be used to connect the 2 sides ...the size of the outside diameter of 3/4 gal. steel pipe? Or any suggestions ?? Thanks ~David

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My thought is 45 degree street elbows, two of them threaded together per cylinder will make a nice swing joint and can correct the most random angle I have worked with.

after all this I`ve decided to go with duals....straight up ....a 5" 3/4 pipe out of one side ....a 8" pipe out of the other( to bring them on the same plane) ....with 45* elbows on the ends and each having a sausage muffler on .....then aluminum up stacks on each with a flapper on top ...the stacks will be able to be removed at the sausage mufflers for getting under low bridges. I like not mixing the 2 pipes up and I think the sound will be enhanced .....a cross support can be clamped between the 2 down low for added stability .....so....that`s the direction I`m headed ...thanks again for all the good ideas....David