Mercury Racing, the Fond Du Lac, Wis.-based leader in high-performance marine engine-building doesn’t divulge sales figures. Company president Fred Kiekhaefer and the rest of his team consider that kind of information proprietary. However, based on the number of high-performance boats powered by Mercury Racing 525 EFI engines, it’s a safe bet that the naturally aspirated, electronically fuel-injected powerplant is the most popular engine in the Mercury Racing line.

The Hardin Marine Stage 1 turbocharging kits for the Mercury Racing 525 EFI will be priced at less than $12,000.

The Hardin Marine Stage 1 turbocharging kits for the Mercury Racing 525 EFI will be priced at less than $12,000.

In fact, thanks to standard-setting reliability, durability, and performance, it could be the best-selling engine in the company’s history. But again, Mercury Racing doesn’t hand out sales numbers.

That makes the engine, once it’s out of warranty, an equally popular choice for power upgrade kits, which until now have been in the realm of add-on superchargers, better-breathing exhaust systems, and remapped computer-control modules. But with its new HTX2 turbocharging kit for the 525 EFI, Hardin Marine is looking to break new after-market, power-boosting ground.

“With the turbocharged, quad-overhead cam 1,350 and 1100, Mercury Racing raised the bar on everyone,” said Scott Price, the owner of Hardin Marine. “Those engines are complete game-changers. Turbocharging has been around a long time, but just a few years ago most people wouldn’t even consider it in a marine application. But the game has changed.”

When the kit goes into full production this spring, it will be offered in a 750-hp Stage I version and an 850-hp Stage II version. With exhaust, the base price of the kit will be $11,995.

Worth noting is that a Bravo One XR drive, which is standard on the 525-hp engine out of the factory, will not stand up to a 750-hp engine. That means buyers of the kit also will need to either replace or upgrade their stern drives. Also worth noting is that a large-pitch propeller will be required to put the extra power to good use. These aren’t “hidden costs,” they’re just costs that go-fast boat owners in their drive for more power and speed often fail to consider.