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I am thinking of buying a boat with a cummins 4bt 3.9 150hp 1994. so I have some questions about the engine.
  • is it a good engine?
  • is there a lot of vibration?
-what do I need to do to get it to 180-200hp and 350-450 torque?
 

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-nobody here will say that it isnt a good engine
-yeah theyre paint shakers
-literally turn up the fuel and apply more air to hit the hp number it probably already hits the torque number (adjust fuel screw on pump, swap on an he221 or just more boost with stock hx30)
 

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Beer Money, did you notice he said boat. This is a marine engine so turbo swapping isn't much of an option since those are water cooled. The VE pumped 150 HP. Not as powerful as the 250 HP P pumped model but more civilized and had less problems. Sunmar,It would be considered a good engine .but not sure what options you have as far as turning up the power. In theory it might be done but the turbo is going to be your limit. I believe the stock turbo was an H1C and it won't go much higher than the 150 HP level. There are no HX30W or HE221W that can be adapted. The 250 HP used an HX35 but it also had a P7100 injection pump feeding some 5x.012 injectors.
 

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Beer Money, did you notice he said boat. This is a marine engine so turbo swapping isn't much of an option since those are water cooled. The VE pumped 150 HP. Not as powerful as the 250 HP P pumped model but more civilized and had less problems. Sunmar,It would be considered a good engine .but not sure what options you have as far as turning up the power. In theory it might be done but the turbo is going to be your limit. I believe the stock turbo was an H1C and it won't go much higher than the 150 HP level. There are no HX30W or HE221W that can be adapted. The 250 HP used an HX35 but it also had a P7100 injection pump feeding some 5x.012 injectors.
my understanding of the marine engines was that the manifolds were water cooled but the turbo was still of a standard design, is that not the case?
 

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No it is not the case. Below are photos of what the H1C turbo on those engine looks lie. Totally different animal than the land use turbos. The turbine housing is totally water cooled along with the exhaust manifold and intercooler if one is present. The engines have a special water pump that circulates lake or sea water to provide cooling. Photo below shows that pump which mounts where our road engine normally have the power steering pump. The engine come in a 4b, 4bt, and 4bta versions. The b was usually a lower power unit used for generators. The bt and bta were the drive engines. The a was a slightly higher HP with the aftercooler. In the last photo below you can see that you'd almost not recognize this as a 4bt. Everything on the outside is special and even internally the pistons are different. That's why you might pick up a used 4bt road engine for around $4000 and a marine version might go $10,000. That external marine hardware is super expensive.
 

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I am thinking of buying a boat with a cummins 4bt 3.9 150hp 1994. so I have some questions about the engine.
  • is it a good engine?
  • is there a lot of vibration?
-what do I need to do to get it to 180-200hp and 350-450 torque?
Many moons ago I had a friend who put a box truck 130hp 4BT into a 20' inboard. Rather than purchase the expensive but proper marine 4BT water cooled exhaust manifold and water cooled turbine housing, he sent both his out for a thick ceramic coating, along with the raw water cooled down-pipe. "White Lightning" ceramic coating if I remember correctly. He also ran a low speed bilge fan to move any engine compartment heat aft and out the console and gunwale vents. I only rode with him a few times after that but engine over-temp warning never tripped and the heat coming out the vents after 20 mins of steady cruise was not excessive by any measure. He had more trouble finding the right prop to reach cruising/planing speed under moderate boost while still allowing a nice slow trolling idle. Plenty of marine posts on here to soak up some good info/opinions.
 

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Viking, you can use the land engine in a boat like that but they generally don't have the power like a marine engine unless you make some changes. The 130 HP would have been the P pump 4bt. The same type engine in marine was 250 HP. Land engines normally had a 2400-2500 RPM governor while marines were 3000 RPM. The VE pump land engine was 105-120 HP while the marine version was 150-160 HP. Also, boat engines had a special crankshaft balancer to cut down on the vibration. Although the engine may not overheat, having an exhaust manifold and turbo with a temperature hitting 1000 deg F is not a good thing inside a boat which may be wood or fiberglass. Engine compartments can often be cramped and poorly ventilated. and having a super hot exhaust pipe running through the side of the boat isn't the best idea either.
 

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Viking, you can use the land engine in a boat like that but they generally don't have the power like a marine....
Yes, I know he did the usual tweeks to raise the power level ..injectors, 3200 lb gov spring, 60 lb valve springs, timing etc. Not sure he had it up to the 250hp marine rating, but it was certainly higher than 130hp when he finished. Failed to mention he also said he double wrapped (out of necessity) the entire stainless exhaust pipe from turbine to exhaust tip, in ceramic high heat exhaust wrap. With no heat exchanger cooling of the manifold/turbine to help off-load some of the exhaust heat, the exhaust downpipe ("riser/elbow" in boat lingo) was solely responsible for all the gas cooling via raw water injection into that pipe. Side benefit of the hotter manifold/turbine gas temps was quick spooling to get up on plane. He used a 45* turn-down tip at the stern - to avoid steam cleaning hapless swimmers on the rear platform.
 

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I am thinking of buying a boat with a cummins 4bt 3.9 150hp 1994. so I have some questions about the engine.
  • is it a good engine?
  • is there a lot of vibration?
-what do I need to do to get it to 180-200hp and 350-450 torque?
I have a boat with Twin 4BTAs at 250 hp. They are a good engine and will last a long time if taken care of (like any engine). They do vibrate but as soon as off idle they are smooth. I changed my 20 year old engine mounts and that reduced vibrations very much. I removed my factory raw water system two years back and installed a belt driven pump (off the crank) that has been excellent. Not sure what you can do to get more hp, you might try the forums at Seaboard Marine, sbmar.com I think.
 
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