Mercury Racing Releases DOHC LS7 Called The SB4 7.0

With all the speculation these days on whether or not the Gen V LT engine will eventually go dual overhead cam, the interest in seeing how that application would perform is high. Luckily for you, you don’t have to wait to find out. Mercury Racing’s new SB4 7.0 has now answered the question for us and the results are more than just good.

You may recognize the Mercury moniker from the LT-5 that motivated the ‘90s Corvette ZR-1. That DOHC 5.7L engine would go on to become the stuff of legend—and deservedly so. The engine actually set a record for highest average top speed over the course of 24 hours at a blistering 175.885 mph—a record that stood unbested for decades. Needless to say, Mercury knows a few things about building high-performance V8s.

Their newest offering is based on an LS7, displacing 427 cubic inches. However, other than borrowing the basic architecture from the LS, it has a lot less in common with the standard push rod variant than you would think. Obviously the biggest changes were on the heads, but several other factors had to be considered first. The largest of which was the oiling system. Significant changes had to be made in order to keep the whole shebang happy.

The heads themselves were designed in-house by Mercury in their Wisconsin-base facility using computation flow dynamics (CFD), amongst a myriad of technology that allowed them to perfect the design. The engine still retains a timing chain, though it’s been swapped out for a dual roller setup. However, instead of driving the camshaft, it merely is driving a mandrel that takes the camshaft’s place. Attached to that mandrel is a cog that drives the timing belt system responsible for operating the unique heads.

The belt specifically drives the exhaust camshaft via a cog that houses a pendulum damper in order to dampen any valvetrain vibrations. The exhaust cam then, in turn, drives the intake cam via a gear setup that uses a “scissor” like methodology to keep the two gears in phase at all time, ensuring no noise from the valve train.

From there, the camshafts act on the valve using a finger follower system that allows them to be shimmed for proper clearances. The intake manifold was also designed in-house by the team at Mercury Racing and allows the marvelous mill to pull all the way to 8,000 rpm. However, it produces peak power at 7,500 rpm and produces 775 horsepower and 570 lb-ft of torque—very healthy for a naturally aspirated bullet.

On top of that, Mercury says the idle characteristic are superb and you would hardly notice that it wasn’t a standard LS7 if you didn’t know what was under the hood. Obviously, in order to turn that kind of RPM, the internals were strengthened to withstand the added stress. Running the engine is Mercury’s own proprietary ECU and software that come with the engine and, again, were developed in-house.

The throttle is modulated by twin 80mm throttle bodies operated by Mercury’s own throttle motors. The bullet is fairly high compression with an 11.7:1 ratio. But all of that brings us to the golden question: will it fit in what you’re building? While it may look substantially wider than an LS, the proportions are not too far off and more of the difference is located in an area that shouldn’t be a huge problem for most. For comparison’s sake, the engine is shorter than an LSA and almost the same height as an LS3. Width wise, they tell us that the engine is a couple inches broader.

An even more exciting prospect is the fact that Mercury Racing is now working with the Roadster Shop and the SB4 will be available in a myriad of chassis, including their new ’66-77 Bronco chassis, in which it was on display. However, the guys from Mercury have been testing it in an Ultima GTR–something we would really like to drive (stay tuned). We can’t wait to see this in something crazy and possibly swap one into something ourselves. We never thought we could love something without push rods so much, but here we are. 

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About the author

Chase Christensen

Chase Christensen hails from Salt Lake City, and grew up around high-performance GM vehicles. He took possession of his very first F-body— an ’86 Trans Am— at the age of 13 and has been wrenching ever since.
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