Dynoing A Supercharged 565-Cube Marine Big-Block Built For The Water

It’s no secret that the basic recipe for a killer marine engine is to take a hot rod combination, overbuild it by about 50-percent, and then beat the ever-loving snot out of it on the water. While there are plenty of marine-specific engines, the coolest hunks of iron on the water are the automotive engines that have been purpose-built (or rebuilt) specifically for an aquatic life.

So, anytime we get a chance to see one come together, we’re all about it. This supercharged big-block Chevy combination is being put together by Prestige Motorsports, and is actually part of a pair for someone with a water-based speed addiction. The Horsepower Monster’s Jeff Huneycutt tagged along for the build and shows every facet of what goes into a killer marine big-block engine.

Don’t Call It A Boat Anchor

Of course, the foundation of any combination you plan to cram full of boost and run wide open for hours on end needs to be a strong block. So the team at Prestige started with a Merlin IV iron block from World Products. Besides the standard features of the Merlin IV like priority-main oil, extra-thick cylinder walls, and additional main-web support, this particular block has been taken to just .025 inch shy of its maximum bore diameter at 4.600 inches, and has had the deck cut for fire rings.

The World Products Merlin IV iron block has been outfitted with fire rings to more reliably contain the combustion pressure created by the boost. In order keep the crank spinning smoothly, King's pMaxBlack line of bearings were used in both the mains and the rods.

The block has been outfitted with piston squirters and fitted with King XP pMaxBlack main bearings. Resting in those bearings is a forged Eagle crankshaft with a 4.250-inch stroke. Hanging off the crank are a set of Eagle 6.385-inch forged H-beam rods with King XP rod bearings. Filling the holes are a set of custom forged JE pistons, designed with a 13cc inverted dome to keep the compression ratio in check.

To top off the combination, Prestige opted for a set of their in-house cylinder head castings, that are ported at their in-house CNC department. Specifically designed as a marine version of their usual 24-degree BBC cylinder head design, the intake ports are 350cc with a 121cc chamber. The “marine” moniker comes with some additional exhaust valve guide clearance, 1.800-inch Inconel exhaust valves, and heavy-duty 2.300-inch stainless steel intake valves.

Prestige used a set of their own aluminum 24-degree BBC castings, that were then CNC-machined in-house for this specific application. 350cc intake runners, 121cc combustion chambers, stainless intake valves, Inconel exhaust valves, and a little extra clearance on the exhaust valve guide, are just a few features of these impressive pieces.

Controlling those valves is a hydraulic valvetrain designed for maximum durability. The hydraulic-roller camshaft from COMP Cams measures in at .399 inch of lobe lift on the intake and .389 inch on the exhaust. The lobes have a duration of 259 degrees and 267 degrees, with a 114-degree lobe separation angle. The cam is controlled by a Rollmaster double-roller timing set.

Riding on the cam lobes are a set of hydraulic-roller lifters, using a dogbone-and-spider retaining system instead of the more common aftermarket tie-bar setup. A set of 7.800-inch intake 8.600-inch exhaust pushrods actuate the Jesel Sportsman Series aluminum shaft-mount 1.7:1 rocker arms. Doing a little math, that makes for .678 inch of gross intake valve lift, and .661 inch of gross exhaust valve lift.

The Jesel Sportsman Series shaft-mount rocker arms use individual shafts and bases for the aluminum 1.7 rocker arms. With that ratio, the camshaft measures out at .678/.661 inch of lift and 259/267 degrees of duration at .050 inch of lift

The Crown Jewel

Topping off the combination is a piece of automotive art, that performs as good as it looks — a Whipple Gen-V 3.8-liter twin-screw supercharger. Having an intercooler built into the intake manifold is a familiar sight with a Whipple supercharger, but what is genuinely unique about this marine setup, is that the fuel is injected into the supercharger ahead of the rotors, just inside of the inlet. All eight 120 lb/hr injectors are controlled by a Holley EFI ECU and are mounted in a single, short fuel rail, installed at the back of the blower.

While the Gen-V 3.8-liter Whipple supercharger is similar to the unit you'll find in automotive use, the injector setup in the marine application is extremely unique. The eight 120 lb/hr fuel injectors mount into a single fuel rail, and the inject fuel just after the massive throttle body, before the rotors.

Since it’s a marine engine, accessories aren’t really critical, so the blower is driven by a straightforward pulley system consisting of a crank pulley bolted to the Innovator’s West damper, a tensioner, an idler pulley, and the supercharger pulley itself. They are all connected by a 12-rib Gates “green” serpentine belt. The pullies were originally configured for low boost (about 6 psi) to start. That break-in configuration was good for 910 horsepower at 6,400 rpm and 891.9 lb-ft of torque at 4,800 rpm.

Not satisfied, the team dropped the blower pulley size by .375 inches which added approximately 2 psi of boost, for a total of about 8 psi. That small change netted about 60 horsepower and 60 lb-ft of torque at the peaks, with a final number of 973.4 horsepower at 6,100 rpm and 953.7 lb-ft of torque at 4,700 rpm, on plain-old pump gas. Not bad at all for something that will run all day long and have ultimate reliability on the water.

Here you can see both the low and high boost numbers. While low and high are relative terms, as the boost levels are only 6 psi and 8 psi, respectively, you can see the minor change was worth significant power. From 910 horsepower and 891 lb-ft to 973 horsepower and 953 lb-ft of torque — all on premium pump gas. Imagine if they turned up the boost even more…

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Greg Acosta

Greg has spent nineteen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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