Boats sustain high RPM loads for extended periods of time and require additional considerations over a car's engine. We explain some of the differences on this 900hp BBC build.
Cory Richards contacted Prestige Motorsports near the end of boating season 2016. He was ready to up the ante on his 27-foot pontoon. Richards described what he desired with Prestige owner and fellow boat enthusiast Doug Aitken. After a few phone conversations, they hammered out the blueprints of what would be the ultimate party boat.
Although this ride would be skimming across water, the engine needed to have a good amount of low end grunt to get it up and moving, especially with a handful of Cory’s friends aboard. A big-bock stroker engine was the natural choice. Long stroke engines give an extra hand in the torque department by providing a longer lever (crank throw) and additional cubes over a factory stroke. On top of that, Aitken and Richards decided on a Whipple supercharger to pack an even bigger punch and add to the persona of the Playcraft Extreme boat.
Once the generals were decided upon, Aitken and his crew got to work on the details. Anytime an engine is going to be used in a marine environment, there are specific areas that Prestige pays close attention to. Bearings, valves and oil pans are automatically upgraded on their marine packages. In this case, the supercharger added to list block, rotating assembly, head gaskets and hardware. This engine also needed to run on pump gas that will be readily available at the lake. Fortunately for Richards, Prestige came through with the complete package.
Designing a Short-Block for Extended, Extreme Loads
The big-block Chevy displaces 540 cubic-inches through its 8 cylinders. A cast iron block from Dart is used to house the beefed up rotating assembly. The Big-M is offered in several configurations. Prestige chose the standard 9.800 deck height with a 4.500 bore. Standard features of the aftermarket block include priority main oiling and 4-bolt splayed main caps. Although the block is available in Gen V and VI versions, this build utilizes the old-school Mark IV design. The main reason behind this is the wide selection of parts available for the first-generation design.
Next is the rotating assembly. Stroker engines are quite popular in the land of big-blocks. Big cubic inch engines pound the pavement at drag strips across the world every weekend. The range of available strokes is quite large. However, with the experience and expertise of Aitken and the guys at Prestige Motorsports, narrowing the choice is second-nature.
First, the standard deck height narrows the choices. Second, engines used in a marine environment are subject to extreme loads for extended periods of time. Therefore, the rod length to stroke ratio is an important factor to consider. As stroke increases the rod ratio decreases. This translates into increased rod angles during rotation, which in turn creates higher loads on the piston skirt pressing against the cylinder wall and raises peak piston speed. Both are less desirable for an engine that will see heavy load for extended periods. Third, the compression ratio must also be considered. Increasing stroke adds swept volume to the cylinder. A Callies 4.250 stroke crank with their 6.385-inch Ultra H-beam rods fit the bill.
A final, and crucial, factor for consideration is the piston compression height. This is the distance from the center of the wrist pin to the top of the piston crown. As stroke increases, the rod length and/or piston compression height must be adjusted to keep the piston from protruding out of its cylinder bore. However, there are important factors to be considered when changing piston compression height.
A short compression height has advantages, including less reciprocating weight and higher rod ratios for a given stroke. On the other hand, moving the wrist pin up reduces available real estate for the ring pack and material thickness may be reduced in areas of inverted dishes and valve reliefs. In a boosted application ring location and material thickness are critical.
Prestige has relied upon the expertise of the engineers at JE Pistons to help navigate through the piston selection process. With the assistance of Finite Element Analysis (FEA), JE offers piston designs that can withstand the extreme abuse of a boosted marine engine. After considering all the factors mentioned, Aitken and his team settle on a custom slug from JE and piston rings to suite.
Building the Engine
Once the rotating assembly has been balanced, measured and pre-assembled, machinist and short-block guru Cody McCleary fits each main journal and connecting rod with individually selected bearing halves to achieve the desired oil clearances. Prestige uses Calico coated bearings on all their marine based engines. Each measurement is recorded, oil clearance is calculated, and McCleary assembles the short-block. It then makes its way to the lead engine builder, known simply as Senior due to his 30-plus years of experience, for final assembly.
Senior starts by sliding in the custom ground hydraulic roller camshaft and attaching a billet steel, dual roller timing set. The cam is degreed and then sealed off with a cast aluminum timing cover. The block is rolled over on its stand and the oil pump and pickup tube are bolted into place. All the main and rod bolt torques are double checked prior to oil pan installation.
A large capacity marine grade oil pan is used. Marine pans provide a large quantity of oil to keep oil temperatures in check during extended use they will see on the water. The pan is also powder coated for protection against corrosion and a clean appearance. A billet aluminum SFI certified balancer from Innovators West is pressed onto the crank snout, and a solid timing pointer is installed and set to zero degrees at top dead center on cylinder one.
Tie bar roller lifters are lubricated and slid into their respective bores. Next comes the Multi-Layered Steel (MLS) head gaskets, standard for boosted applications at Prestige Motorsports. Aluminum cylinder heads from AFR are installed over ARP head studs. Head stud nuts are torqued in steps to insure even clamping force.
Prestige has already upgraded the valves with extreme-duty versions to withstand high exhaust temperatures seen in marine applications. The springs have also been upgraded to match the custom grind camshaft from Comp.
One-piece 3/8-inch pushrods are carefully dropped into position. Scorpion roller rocker arms are installed onto the ARP rocker studs connecting the pushrod to the extreme duty valves. Lifter preload is measured and set. Rocker geometry and spring retainer clearance are double checked. The intake manifold is also powder coated black to match the 4.0-Liter Whipple supercharger. A set of polished aluminum valve covers seal up the valve train and provide a sharp contrast to the all-black engine.
Holley’s HP ECU and wiring were used along with a set of Accel injectors. The Whipple unit hides the eight injectors at the back of the supercharger for a clean look. Side mounted water and power steering pumps are installed along with an alternator, pulleys and belts prior to the engine being set on Prestige’s in-house engine dyno.
On the Dyno
After a warm-up period and initial tuning, the 540 is ready for a round of break-in loads to verify the integrity of the build before a full sweep test is performed. After a series of minor adjustments, the engine is putting out a conservative 765.5 pound-feet of torque and 777.7 horsepower with a four-inch pulley on the Whipple.
Aitken decided to spin the blower faster by reducing the pulley size one-inch. Senior installed a three-inch pulley, adjusted the belt size, and flogged the engine some more. Torque and horsepower were increased to 892.1 and 882.8 respectively.
The larger pulley was re-installed and one last dyno pull was performed as a verification the engine was still in good health. Richards will start out with the larger pulley knowing that he can switch to the smaller version if the extra power is desired. Once the heat gets turned back up, look out for Richards and his Prestige-powered Pontoon disrupting the waters in southeast Iowa.