Last year at SEMA, Mercury Racing brought a 32-valve cylinder head designed for the LS cylinder block simply to test the market reaction. Now the marine powerhouse has a full 7.0-liter crate engine sporting those DOHC heads for sale at less than $30,000.
Called the SB4 7.0, the V8 is rated at 750 horsepower at 7,500 rpm on pump fuel. Maximum recommended engine speed is 8,000 rpm.
The cam drive is somewhat reminiscent of the old Ford 427 SOHC engine in that there is a traditional dual roller chain timing set on the front of the motor, but there is no camshaft in the tunnel. Instead, the cam gear supports pulleys that turn the respective outside cams on the cylinder heads. The inside cams are gear driven off the outside cams. Overall, the belt drive is similar to the wicked QC4 9.0-liter, twin-turbo crate engine Mercury Racing showed off at SEMA a few years ago.
“The cam timing is specific to this engine tune,” says Erik Christiansen, general manager at Mercury Racing.
Basically, the cam timing can be less aggressive than a high-horsepower 2-valve LS engine because of the extra valve openings in the head. Valve sizes are 43.25 mm intake and 36 mm exhaust.
The bottom end of the engine is familiar LS7 aftermarket hardware with a Callies forged steel crank, Carrillo H-beam rods and 11.7:1 Mahle pistons. Bore is 4.124 inch and the stroke is 4.000 inch. The magic comes from the cylinder heads and intake manifold. Incoming air passes through dual throttle bodies into a common plenum before distribution to the cylinders through wide, rectangular-shaped runners. The fuel injector for each cylinder is positioned in the head near the back of the intake valves, not in the runners.
“We tried to keep the plenum on the small side for quicker throttle response,” adds Christiansen.
Although the cylinder head leverages some design features from the QC4, the exhaust ports were patterned after the LS7 cylinder head.
As with any true-blooded boat racer, Mercury Racing placed an emphasis on aesthetics. Different colors are available for the block and top end, and the overall appearance is quite sanitary.
Interest in the QC4 has remained high from custom car builders, especially for exotic show cars, and one OEM with ideas of another supercar has expressed interest in it. Therefore, there should be even more curiosity about the SB4 due to its lower price and tighter packaging. Total weight is expected to be just under 500 pounds with dimensions slightly larger than a stock LS7.
The engine comes with a dedicated ECU and throttle-by-wire controls.