Stock air inlet cover is highly restrictive, as it requires airflow to turn 180 degrees around rear of housing to enter stock butterflies.
Once again, reader inquiries from Outboard Tech have compiled to dictate the direction of another hop-up article aimed at a specific reader audience. This time, it's owners of stock Mercury/Mariner 3.0-liter (185-cubic-inch) EFI engines, those produced between 1995 and today. Note first of all that 1998 and later engines cannot, by law, be modified to produce any more power than "as manufactured." The latest EPA smog laws prohibit alterations to any 1998 and newer two-stroke engines that might increase their hydrocarbon (HC) output. At this point, there are no procedures in place to test engines locally, so, for awhile, many will probably modify their new engines anyway. The new laws don't cover engines used in competition, so if you're planning on racing yours, modifying it may still be okay.


The three-liter Merc is not a typical "hot rod" engine, as most that opt for Team Black power usually install the higher-revving small-block 2.5-liter models. Lately, though, interest has developed in the big-cuber, mainly due to the additional low-end grunt potential its larger-displacement block offers. Unfortunately for tuners and tweakers, there's not much in the outboard aftermarket being produced for these engines just yet.

Merc's 3.0-liter 225 and 250 have started to become more popular as heavy-duty, high-performance power plants for larger sport boats and bass fishing hulls.
The three-liter V-6 started life at Merc as a 1994 model, introduced as a carburated 225-horse "offshore" model. Built mainly to combat sales of OMC's successful Ocean Pro and Ocean Runner three-liter engines, the new 225 was produced and sold as an offshore fishing engine. In 1995 it was offered again with carbs, but also with EFI. The year 1996 saw the introduction of the 250-horse model, and digital EFI was introduced. Today, the engine is also the basis for the new OptiMax offshore models with direct fuel injection (DFI), and also provides the platform for the awesome 300 Pro Max from Merc's High-Performance division.

So how can a basic 225, clamped to the transom bracket of today's 20-plus-foot hot outboard, produce more power without sacrificing reliability? In addition, can it make that power without running premium fuel and hand-mixing the oil? In a word: yes.


Tony Brucato, an outboard enthusiast from the Fort Lauderdale area in Florida, has been producing his SVS (Stackable Velocity System) intakes for Mercury and Mariner outboards for a few years now, with continued success. His first model, built for the race-style 2.4 and 2.5 EFI engines, provides more top-end speed as well as midrange power. In late 1996, he completed development on a second model for 2.5-liter Pro-Max engines, with similar results. His latest version is just what the doctor ordered for 3.0-liter models, and testing has shown remarkable performance gains for such a simple bolt-on product.

The key step in SVS installation is making sure the slide unit moves freely without binding.
The SVS works by providing more airflow for the engine to process, therefore allowing it to make more power at all rpm levels. Remember turning the air cleaner lid upside down on the family sedan to make it suck in more air? This is a refinement of that time-honored concept. Basically, the Brucato SVS replaces the stock EFI air inlet cover with a machined guillotine-slide valve assembly that opens progressively as more throttle is applied. The stock air inlet butterflies, located on the rearward side of the inlet cover continue to open normally. The SVS simply provides more air for the engine to process.

The installation is simple and quick; any home mechanic with a good working knowledge of outboards can perform the job in an afternoon, complete with setup and testing. Basically, the stock air inlet cover is removed and replaced with the SVS unit. The stock throttle cam and linkage are augmented with pieces supplied in the SVS kit to provide a progressive link to open the SVS throttle slides. During installation, the only critical procedure comes when placing the slide assembly-made from a plastic-type fiber material-into the machined aluminum base housing and then installing the aluminum cover plate. If this is installed incorrectly, it may bind when opening or closing.

After installation, the original EFI components that were temporarily removed (the throttle position indicator and air temperature sensor) are reinstalled, and then the linkage adjustments are performed. This is the other critical part of the job, as incorrect adjustments can cause the installation to perform no better than the stock setup! It's important to remember that the stock butterflies must open and close correctly and fully, and the SVS slides should open progressively with no binding or catching. It must also be remembered that, after the initial adjustments are performed according to the SVS instruction sheets (which, by the way, are well written, easy to understand and supplemented with good detail photos), the adjustments must be checked with the throttle lever or foot throttle hooked up. The stock butterflies and SVS slide plate must open fully as well as close completely. It's a good idea to have a factory service manual in hand, just in case the stock throttle and/or timing adjustments are off and must be reset.