Mercruiser 470 (3.7L) Marine Engine Options

Question: What’s the best direction to go when replacing the old Mercruiser 3.7L/470 marine engines?

Unfortunately there is no single good option for this when looking at a complete re-power. The 470 was originally developed by Mercury Marine specifically for it’s purpose; to power boats. The inline configuration allowed for easy draining, a single intake/exhaust manifold was cheaper than two, etc. The engine was also a large displacement engine for its size and therefore made a tremendous amount of torque because of the stroke and displacement. On top of this Mercury utilized their die casting expertise to produce a light weight aluminum block and combination with the existing Ford cast iron 460 cylinder head.

To go up in Hp you will have to go with the typical V-Configured  350 engine which will also require a different drive ratio and propeller. With any changeover to the V engine configuration be it V6 or V8 this will also require completely rebuilding the stringer system in your boat. Many customers ask about replacing the 470 engine with the current 3.0L engine since they are also are an inline configuration. The problem with this is that the 3.0L makes approximately 135 Hp & 180 Lb-Ft of torque where the 470 made 190 Hp and approximately 275 Lb-Ft of torque. The 3.0L engine is simply too small and does not make enough torque.

Recommendation

Therefore the prevailing direction for 99% of boat owners in this position is to go with the remanufactured 470 longblock. The remanufactured longblocks are of a very good quality and have a 24 month warranty. This is important versus rebuilding realizing this was not a standard automotive product and therefore most local rebuild shops do not have the experience to produce a comparable, good quality product.

In some cases certain customers really love their existing boat but prefer more horsepower/torque. If this is the case for you it may be worth the time and investment to investigate changing over to the larger displacement “V” configured engine, however in 99% of the instances the only viable option comes down to replacing the longblocks or simply changing boats.

Installation Drawings for reviewing specific dimensional differences (open is separate windows)

470 (1976 Model) Installation Drawing (Select Link)

470 (1978 Model) Installation Drawing (Select Link)

3.0L (Inline 4 Cylinder) Installation Drawing (Select Link)

4.3L (V6) Installation Drawing (Select Link)

5.7L (V8) Installation Drawing (Select Link)

Tech Tips (Select Link)

Remanufactured Longblock Product (Select Link )

Tags: 3.7L, 470 inline engines, marine engines, marine longblocks