The Mercury/Mariner 2.5 260-hp EFI is a popular outboard. Witness that any time hot-boaters gather, the 2.5 EFI is easily the engine of choice. But what about making it "meaner"? Today the chinning bar has been raised, first by aftermarket hopup shops and then by Mercury Racing (by introducing this year's upgraded and updated 280-hp version). As hot as the original 2.5 was, owners of this potent 260-horse outboard have been looking for more power ever since its introduction in 1992.

SVS installation really woke up bottom end and midrange punch on Tiger's SS-2000 drag hull.

Aftermarket hot-rodding has ranged from wilder porting, to better exhaust tuners, to shaved and blueprinted heads, and then to lightened flywheels, crankshafts and modified fuel injection components. High-end shops like Diamond Marine in Fort Lauderdale have made the 2.5 their bread and butter, cranking them out in Various stages of tune from mild to all-out wild. While Diamond's mods tend to center around labor-intensive operations, many 2.5 enthusiasts have been after the so-called bolt-on mods to ensure that the engine can remain stock otherwise. In some cases, this is so the engine can be converted back to stock when it comes time to sell and, in others, so an engine can be raced in a stock class.

Tony Brucato of Brucato Machine & Tool has targeted the bolt-on marketplace with his very successful Stackable Velocity System. Born of a need to increase air-flow and air entry efficiency beyond what the stock Mercury air horn assembly offers, the SVS intake assembly offers a true bolt-on modification that, as we'll prove in this latest test, actually changes the performance of the engine in a significantly positive way. The SVS was designed around the principle that the airflow differentials inherent in the stock Merc air horn inhibit acceleration through the entire powerband. This is due to the fact that the horn feeds the center two cylinders with direct airflow, while the upper and lower cylinders receive their air later (and via a more indirect path). This is because the stock air inlet is positioned directly in front of the center two cylinders; the upper and lower cylinders' intake slots are well out of the direct airflow path, tucked into the upper and lower recesses of the air horn assembly. In addition, the SVS can be tuned for proper intake runner length by simply adding or removing black aluminum spacers to each of the three intake inlets.

The SVS system consists of an intake cover plate machined with six, equal-sized slots that match perfectly with the engine's intake tracts. A fiberglass guillotine slide plate controls airflow. This slide plate has its own inherent advantage over the stock air horn's rotating butterfly shutter; simply put, the slide disappears completely from the airflow when opened, while the butterfly leaves an obstruction directly hampering clean airflow. Machined aluminum linkage and stainless hardware couples the SVS intake system to the stock Merc throttle arm and cable assembly. During replacement, the stock reeds and reed cages are used; they're simply reattached to the SVS intake plate. The stock air horn and intake manifold are replaced entirely. The ECU (Electronic Control Unit), or "brain box," simply remounts to the SVS intake. The machine work and attention to detail of the SVS are truly fantastic; adding it to the front of a 2.5 really dresses the engine up. The installation instructions are clearly written and easy to understand, and each kit comes complete with all mounting hardware needed to complete the swap.