BluePrint MBP3550CT GM 355 Base Marine Engine, Cast Iron Vortec Heads

This new BluePrint MBP3550CT is a GM 355 cubic inch base marine long block topped with cast iron Vortec cylinder heads and a flat tappet camshaft. Output lands at 365 horsepower, with 390 ft-lbs of torque backing it up, and compression sits at 9.5:1. As a base engine it ships without carburetor, intake manifold, or distributor, so the installer carries those over from the existing boat.

What is in this long block

The block is a seasoned 4-bolt main casting bored .040 over to a 4.000-inch bore with a 3.480-inch stroke, sonic tested for wall thickness and fitted with an externally balanced cast steel crankshaft, Chevy heavy beam rods, and hypereutectic pistons. Intake duration measures 226 degrees and exhaust duration 236 degrees, with a 112-degree lobe separation on the flat tappet cam. Valve covers, oil pan, and timing cover are installed at the factory.

Before you bolt it in

What oil does BluePrint recommend? Non-synthetic 10W30 for break-in and ongoing service. Does the cam need anything special? Yes, a zinc additive is required for this flat tappet setup to protect the lobes. Can this run an EGR system? No, this long block is not built for EGR applications, so plan your intake accordingly.

Coverage and part number

Coverage runs 12 months, unlimited hours, strictly for pleasurecraft use; commercial marine duty is excluded. The part number is MBP3550CT, and condition is new.