The reason behind the popularity of Mercury Racing’s 525EFI engine is so simple: It’s reliable. Make that super-reliable. Only a fool would modify the 525-hp stalwart of the Mercury Racing engine line in any way while it is still under factory warranty.

Maintaining that high level of reliability was paramount for Ray Brody and his crew at Raylar when they developed their new upgrade package for the 525EFI. Priced at $14,930 and slated for release in August, the package reportedly raises the engine’s output to 675 hp.

“We’re offering the kit on a ‘rework’ basis,” Brody explained. “Customers send the engine to us and we install new cylinder heads, new intake manifolds, new pistons, a new crankshaft and more, and we blueprint the engine, just as they do with the 525 when it’s new at Mercury Racing. We end up taking the displacement from 502 cubic inches to 540 cubic inches, but the engine is built on exactly the same footprint as the original 525. It fits right into the same place and uses the same exhaust system as the original.”

According to Brody, the upgraded and still naturally aspirated engine—called the Raylar 675EFI—will run on 89-octane gasoline and be offered with a one-year “recreational warranty.”

“We’ve been working on it for a year-and-a-half now, and our goal was to create an upgrade package for the 525 that would deliver the same reliability and durability as the original 525,” he said. “Now with all the right parts inside, we have a nice 540-cubic-inch engine that’s not straining to make 675 hp. We actually limited the torque by using a fairly mild cam because the Bravo XR drive has a limit to how much power and torque you can put to it.”