Join Date: Oct 2009
Location: Gloucester, MA
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Re: Cummins 4B 3.3
I really like the 4B engines but they are certainly not the most sophisticated engines out there. The reason that I like them is they are really simple, reliable and very easy to work on. Many people are familiar with the 6B engines which are extremely well regarded.
The primary reason that I would say they are not as refined as other engines is vibrations. These are relatively slow turning engines with only 4 cylinders so there is quite a lot of vibration. Compared to a 6B, it is a lot more. In a vehicle (they came in a lot of vans), it is borderline annoying but I think that you could deal with this in a boat installation. If you did something like an evolution drive, I think that there would be very minimal vibration. Since you are coming from an older Volvo, it is likely to be slightly better on vibration but still way more than the newer Yanmars, Betas, etc. On the noise front, I think that they are really good sounding engines and pretty quiet for their design vintage. The '98-'02 24V 6BT engines were really loud and gave the B series Cummins a reputation for being loud but most of the rest of the line was not very loud all things considered. A good muffler would make it very quiet in my opinion for a mechanical injection engine. Compared to a common rail engine, it will be noisy and vibrate a lot but they are not bad for a mechanical engine.
Unfortunately, Cummins will no longer sell you a brand new 4B due to emissions. They will sell you a rebuilt unit which you can use in a repower situation but not in a new build. It sounds like you have found someone aftermarket who will marinize one though. If you get a OTR 4B, it is one of the easiest engines to marinize but it will still be really expensive due to having to buy a new alternator, starter, heat exchanger, water pump, etc.