View Full Version : ETX/CAT write up in Boating

Farmer Ted
12-18-2006, 07:43 AM
Anyone happen to see this?


Pretty good article that explains how Indmar developed this....

A three-way catalytic converter such as that used on the Indmar ETX/CAT engine “converts” three harmful exhaust components—hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx)—into harmless compounds.

Palladium and rhodium are coated onto a ceramic honeycomb designed to present the maximum surface area. These elements are the catalysts—they assist a chemical reaction without being consumed by it. When hydrocarbon and carbon monoxide molecules in the exhaust encounter the palladium, they break down, recombining with oxygen molecules into water (H2O) and carbon dioxide (CO2). When nitrogen oxide molecules land on the rhodium, they recombine into nitrogen and oxygen.

To function properly the catalyst requires heat and a stable oxygen level. Most of the heat comes from the hot exhaust, though the chemical reaction raises the temperature by another 100 degrees. An oxygen sensor located in the exhaust downstream of the catalyst sends data to the engine’s computer, which then adjusts the air-fuel ratio to avoid a lean (too much oxygen) or rich (too little oxygen) condition.

....Our test boat was a V-drive Master-Craft MariStar 200. After testing with the catalysts in place, the ETX/CAT manifolds were swapped for a standard set. In addition, the engine’s computer was also adjusted for non-cat specs. Both engines are rated at 350 hp.

There was little difference in performance. Acceleration from 0 to 30 mph averaged 5.6 seconds with the cats and 5.3 seconds without. Top speed was 41.0 mph with the cats and 40.9 mph without. Fuel economy, however, was significantly improved by the ETX/CAT system. We measured an 8 percent gain at 30 mph, a 12 percent gain at 20 mph, and a 28 percent gain at idle. The boost in economy occurs because this closed-loop system uses an oxygen sensor to control fuel delivery with more precision than on a standard EFI system.

We used an infrared thermometer to measure the temperature of the exhaust manifolds. After full-throttle running, the standard manifolds were 123 degrees, whereas the ETX/CAT manifolds were 180 degrees. Much hotter but still below the Coast Guard’s limit. Novotny says that the heat of the cat-equipped engine typically causes the temperature within the engine bay to rise 15 to 20 degrees, about the same as if a closed-cooling system had been installed. This rise in air temperature will reduce engine power, so smart boatbuilders will be looking for ways to get more cool air flowing through their engine compartments.

Indmar says that starting in 2007, its 350-hp 5.7-liter V-8 will only come with the ETX/CAT exhaust. It plans to phase in the rest of its engines by the CARB’s deadline. Right now it appears as if MerCruiser and Volvo Penta plan to have a full selection of Four Star engines available in 2008 for sale in California. Three Star engines will be still sold in other states.

Indmar’s lineup is a little easier to alter—it offers only three basic engines (5.7, 6.2, and 8.1 liters). Merc and Volvo need to offer a broader range of engines, including the 135-hp 3.0-liter four-cylinder engine, which has never been offered with EFI but will need to be fuel injected to meet CARB’s 2008 regulations. According to MerCruiser, its low-volume Mercury Racing engines will be exempt from the Four Star rating due to “fleet averaging” built into the rules.