Is it a problem to reduce exhaust hose to 1 3/4?

[Marvin]

So after giving the parts guy at my local yard the complete dimensions to the Y2QM15 on my '79 H33, he sold me a new vernalift muffler with 1 3/4" fittings and hose to match the stern thru-hull. No problems connecting muffler to the thru-hull, though it was quite difficult to get the muffler in place in the skeg under the fuel tank. The problem is that the exhaust elbow is 2 1/4" (according to the book it should be 2" but it has actually ballooned out a bit from 20+ years of corrosion). To resolve this he had me purchase a custom made fiberglass reducer so that I could put a 2 1/4" hose on the elbow which would then connect to the 2 1/4" side of the reducer. The reducer then also fits into the 1 3/4" hose going to the muffler. My question is, will this reduction in size possibly cause back pressure problems for the Yanmar? I don't want to wait until April when I'm afloat to find out.

 

[Dave Simpson]

Exhaust Size Reduction

Seems to me that the reduction you describe should be a safe move. Inasmuch as the larger Yanmars also use nominal 2" connectors and hose, and the larger engines create a great deal more pressure/volume of exhaust. Back-pressure shouldn't be a problem on the face of it.

 

[Steve Dion]

I would check with someone who knows.

Marvin:While the small reduction in size seems insignificant, I would check with someone like Mack Boring. I doubt that anyone increased the performance of an engine by constricting the exhaust. The fact is that most every time they do something to an engine to increase performance they expand the size of the exhaust. I am sure that you engine will run, but when you start small, it is only going to get smaller as you have build up etc.

 

[Ed A.]

check with a yanmar dealer

Im sure you dont want to reduce the size of the exaust if you can help it. Its interesting that the thur hull is small too. If the exaust elbow is that corroded it sounds like you should change that to. its bad when the plug up or spring a leak!

 

[Marvin Muller]

My yard is a Yanmar dealer

That's the problem. The Yanmar parts dealer at my ship yard is the one who sold me this idea for the exhaust system. Very nice guy and I trusted him enough to put the exhaust system in the first place, but I was hoping for a second viewpoint from my fellow Hunter brethren.The more I think about it from my very uneducated viewpoint, restricting the exhaust hose diameter from the intended 2" to 1 1/2" (interior size of the reducer fitting) could create flow pressure problems.

 

[Ed A.]

Call mastry engine

They are in St Petersbrg Fl. Ask for service, they should help you with the right answers.sorry i dont have the number.