Mercury wants (and is required) to have exhaust and noise emissions compliant propulsion. By being responsible citizens (you and us), our freedom on the water can continue. Global regulations have caused larger marine engine manufacturers to invest millions of dollars in research and development. In that work, Mercury developed an on-board microprocessor that controls all aspects of engine operating performance – including fuel management and exhaust emissions. The combination of advanced engine components (hardware), fuel calibration development (software) and extensive testing (more hardware and software) led us to a full line of sterndrives that meet U.S. California Air Resources Board (C.A.R.B.) and Environment Protection Agency (EPA) regulations. But, as we have learned with experience, emissions regulations are ever evolving.
Just when we thought our job was done, by meeting the CARB and EPA regulations in place at that time, more stringent ones were being implemented by the European Union (EU) Recreational Craft Directive (RCD). We had to do additional work to create “global” engines that would meet stringent EU RCD exhaust emissions and noise regulations.
We tackled exhaust gas emissions first. The EU662 SCi is he highest horsepower we could attain and still meet the EU RCD exhaust emissions regulation. Also, we were able to adjust fuel calibration on the 600 SCi to make it RCD exhaust emissions compliant.
Then, noise. Engines, as rigged with a typical through transom exhaust system, didn’t pass RCD noise requirements. Aftermarket mufflers didn’t help. Running exhaust through the prop isn’t an option with our engines: too restrictive.
Our solution was a fully integrated sterndrive exhaust noise reduction system — designed specifically to bring the 600 SCi and 662 SCi into compliance with the stringent RCD noise regulations. Our X-haust Noise Reducer system features a custom y-pipe. It combines the two banks of exhaust from each engine into a single exhaust tube that exits the transom below the water line. An integrated idle relief tube routes some exhaust through the boat, above the waterline, providing a necessary vacuum break. This is referred to as “Stage 1” X-haust. This configuration is sufficient to meet most noise regulations outside of the EU.
The EU RCD noise test requires the boat to pass a sound meter at a distance of 25 meters (82 feet). The boat must be traveling at least 70 kph (43.5 mph), but need not be at maximum speed. To pass the regulation, the average of the two highest results cannot exceed 78 dBA. 78 dBA is quiet! As a point of reference, we measured the sound of water lapping the shore at 75-80 dBA.
Stage 2: To meet the stringent EU RCD noise emissions requirements, Mercury Racing engineers designed a transom mounted muffler which is perfectly sized to achieve the required sound attenuation. The muffler design, connected to the Stage 1 X-haust transom outlet, flows exhaust through two separate chambers connected by three attenuator tubes before exiting the exhaust outlet at the bottom.
The result is further reduction of sound pressure waves without sacrificing power or performance. The transom mounted muffler is completely submerged when the boat is at rest. The muffler outlet directs engine exhaust down and back toward the transom, further reducing noise. We call this complete system, with mufflers, Stage 2 X-haust.
An optional X-haust sweeper header kit has been developed for drive-line engines. The kit includes a revised tailpipe designed specifically for the Mercury Racing sweeper headers. The optional drive-line sweeper header kit is available for all Mercury Racing 502 cu.in. engines to accommodate the use of the Stage 2 X-haust system.
We make X-haust for use with 525 EFI and 600 SCi engines fitted with an Integrated Transom System (ITS) Bravo One XR drive or NXT1 drive options, EU662 SCi and 700 SCi sterndrive engine packages fitted with dry-sump NXT1 and 6 SSM drives. Various Stage 1 and Stage 2 configurations will fit either single or twin engine applications – in both side-by-side and staggered installations (with the port engine forward).
There you have it. You can enjoy your time on the water without the hassle of noise police or upsetting the neighbors.