Yanmar 4JH-TE exaust system sizing

[KnottyBuoyz]

Question. I have a Yanmar 4JH-TE. Exhaust outlet from mixing elbow is 3" Dia. The muffler and exhaust hose that came with the engine has inlet/outlet size of 1-5/8". Somewhere along the line there must have been a reducer of some sort but that wasn't included. I have the service manual for the engine but there's no mention of minimum exhaust size requirements. I don't know much about diesel engines, well actually at this point I know nothing about them, but if they breath better, larger exhaust, they should run better no? Can I go down to 2" all the way back (approx 12' run through water lock, muffler & gooseneck)? That should be better for the engine or should I keep it 3" all the way back?

[CDK]

2 inch seems good to me, assuming that it is an almost straight tube gently sloping down to the muffler. How do you plan to connect it to the 3" exhaust?

[gonzo]

Get an installation manual for the engine. You can probably download it. It has everything you need to know.

[Frosty]

I do have the Yanmar installation manual and the rule is never ever go less than the engine outlet. This is a turbo engine and 2 inch is ridiculously small, if its a power boat use nothing as a silencer or dump bucket.

I have the 6Lp and use 100 mm all the way out. Its not noisy being turbo.

[KnottyBuoyz]

Thnx Fella's. I have the service manual but it says nothing about exhaust hose dia. or back pressure etc.. Since I have to buy all new exhaust components anyways I'm going to go all 3". I don't know exactly where the smaller muffler & hose came from but I'm doubting it was with this engine.