Low Emission Outboards

All four-stroke and direct fuel-injected two-stroke outboards currently available comply with the US Environmental Protection Agency (EPA) 2006 exhaust emission regulations, but the real measure of environmental-friendliness are CARB ratings. CARB stands for California Air Resources Board (mainly for Lake Tahoe) and its regulations are much tougher. For example, CARB 2004 is roughly equivalent to EPA 2006 while currently the toughest set of regulations are 2008 or 'three star'.

The first generation system was released locally in 1997 but has since been upgraded with smaller, more powerful injectors with a higher injector pressure and a back-pressure sensor in the exhaust system to further reduce fuel spray at low speeds.

In FICHT motors the amount and duration of the fuel spray is electronically controlled by individual 'unit' injectors, which currently spray directly into the combustion chambers at 400psi.

A mix of stratified and homogenous combustion is used and below 2000rpm (originally 2800) the air/fuel mix is layered away from the spark plug with an overall ratio of about 40:1, compared to 25:1 during homogenous combustion. This system gives FICHTs incredible fuel efficiency at low speeds but comparable power to carburetted two-strokes further up the rev range. The fuel/oil ratios vary from 300:1 at Dead Slow Troll (DST) to 60:1 at Wide Open Throttle (WOT).

All FICHT models comply with CARB 2007, but some models such as the 135 already meet the CARB 2008 requirements.

Mercury Marine - Optimax

Developed by the Orbital Engine Corporation of West Australia for Mercury Marine, the Orbital Combustion Process was re-named Optimax and released locally in 1998.

The OCP is the only dual-fuel direct injection system. It has two injectors for each cylinder, a mix of stratified and homogenous combustion and a belt-driven 1:1 ratio air compressor. One bank of injectors force air into the fuel rail at 80psi, which is then mixed with fuel pressurised to 90psi and injected into the combustion chambers via another bank of injectors. The fuel droplet size is only five to 10 microns. The fuel/oil ratios vary from 400:1 at DST up to 44:1 at WOT.

All Optimax models currently comply with CARB 2007, while the 135 already meets 2008. According to Kim Schlunke from OEC, all models will meet 2008 in the near future.

Tohatsu - TLDI

Released locally in 2000, Tohatsu's system also utilises the OCP but a Mitsubishi Electric Company (MELCO) microprocessor is used instead of a Motorola unit and a laptop computer is not required for diagnosing engine faults. Also, the fuel/oil ratios range from 450:1 at DST to 50:1 at WOT, but the fuel droplet size is still five to 10 microns.

Tohatsu switched from mechanical to electric oil pumps in its TLDI models late last year. This provides for more precise metering of fuel/oil ratios and has enabled all TLDI models to comply with CARB 2008.

Yamaha HPDI

Yamaha's Mitsubishi-designed HPDI was introduced locally in 1999. A single-fuel system like FICHT, HPDI uses three fuel pumps to raise the injection pressure to 750psi but has automotive-type fuel injectors.

However, the fuel droplet size is 20-30 microns and homogenous combustion with a 25:1 air/fuel ratio is used across the entire rev range. The fuel/oil ratios are 200:1 at DST to 50:1 at WOT.

Yamaha's HPDI currently complies with CARB 2006, but as both the EPA and CARB authorities base 40% of their emissions testing at low speeds, unless Yamaha opts for stratified combustion it may have trouble meeting 2008 requirements.

However, HPDI does have a distinct advantage over OCP in that should the belt-driven high-pressure fuel pump fail the engine can still limp home on the other pumps.

FOUR-STROKES

As of February this year Bombardier Recreational Products Australia had committed to importing Suzuki-built models from 30 to 70hp. The carburetted 30 meets CARB 2006 requirements and the EFI 40, 50 and 70 meet CARB 2008.

Honda

Honda Marine was the first manufacturer to comply with EPA 2006 across the range - eight years ahead of the deadline. Currently all models comply with CARB 2004 and the EFI BF115/130 comply with 2006, but only the BF8/10 and BF175/220/225 meet 2008 requirements.

The BF225 is cleaner than Yamaha's F225A because of its VTEC system, which has a two-stage air intake system and moderate valve lift below 4500rpm, with an aggressive lift and extended opening time above these revs. This results in an engine that operates at maximum efficiency across its entire rev range.

Mercury Marine

While all Mariner and Mercury models comply with CARB 2004, currently only the EFI 30-115hp models comply with 2008 requirements. The 200hp model due here later this year will comply with CARB 2008.

Tohatsu

No four-stroke model currently complies past CARB 2004.

Yamaha

All models meet CARB 2004, but only the EFI F115A and F225A meet CARB 2006 and will need further development to meet CARB 2008.

HOW US EMISSION LAWS COULD AFFECT AUSTRALIA...

Although there are no requirements in place locally to comply with upcoming US EPA and CARB emission regulations, because Australia is such a small market compared to the US, the availability of larger carburetted two-strokes will dwindle.

Bombardier won't make carburetted two-strokes above 175hp and Mercury Marine will probably produce only selected carbie two-strokes above 40hp for specific commercial markets. As Tohatsu intends to continue making carbie two-strokes until at least 2010 (mainly for the Asia-Pacific market), Mercury plans to have Tohatsu build all of its carbie two-strokes 40hp and under.

Tohatsu is concentrating on its TLDI models for CARB compliance and is already working on a TLDI 200 for the US market, but how long its larger carbie two-strokes will remain available depends on Asia-Pacific sales.

As Yamaha has a strong following in the Asia-Pacific market, it will probably continue making carbie two-strokes for as long as Tohatsu does. But marine industry sources believe the company will concentrate on four-strokes for recreational markets, so whether or not HPDI models will be manufactured closer to CARB 2008 is unknown at this stage.

Honda will upgrade all of its models for CARB 2008 compliance by bringing VTEC and/or EFI down the range. It's likely all of these models will be sold locally.