Grand Banks 32 Water Lift Muffler Lehman 120

[Marinex]

Our water lift muffler has sprung a leak here and there and we are looking to replace it. It is currently a Centek I believe, 3.5 inch in and out. The Lehman 120 manifold elbow is 3.5 inches in diameter

However when I took the hose off I found that what I thought I was a hose splice is actually a custom reducer and that the old hose that goes all the way to the back of the boat is only 3" diameter. My plan was to replace all the way to the stern with new hose.

The boat is a 1967 and several things have been 'modified' over the years so now I am left wondering what size should be in there.

I know there are many other boats that used the 120 Lehman engine and I wondered if anyone has run into this when getting a new muffler?


Any shared info would be appreciated!


Thanks, Andy

 

[Doug]

Our 120 Lehman has 3.5” hose. Just replaced it.

 

[Marinex]

Thanks Doug for the assist, you wouldn't by chance know the muffler model info that's in there?

 

[Doug]

Marinex. I’ll check on the muffler when at the boat tomorrow.

 

[Keysdisease]

What you have is probably just fine for direct replacement. It is not unusual for piping from the muffler to be a size smaller than the inlet. This is because the exhaust gas has been cooled by water and has contracted in volume considerably from its exhaust manifold temp and volume. This means that the reduced volume will travel through a slightly smaller pipe and not impact backpressure.

So as for the only real concern, backpressure, you should be fine, and you can always have it measured. Most mechanics should be able to take a pressure reading from a port near the outlet on your exhaust manifold.

The boat is a 1967 and several things have been 'modified' over the years so now I am left wondering what size should be in there.