new Yanmar 2GM20F I went from a 1 1/2" exhaust to a 2" on the new engine - I could have used the 1 1/2" but opted for the two inch to lower back pressure and help this little diesel breath. I have been very happy with the choice. It is a much happier engine now and I guarantee it will run better and longer with the two inch exhaust. It does entail larger hoses in cramped quarters (my case) and of course a new through hull - but for someone going cruising it will be well worth the effort in the long run. ( Have you actually calculated the time difference between sinking with a two inch hole and one with a three inch hole. )