When I got a tour of the new Mercury 150 FourStroke outboard, the exhaust manifold caught my eye. Its smooth shape is obviously designed to help encourage efficient exhaust flow, and Merc told me its location away from the adaptor plate means less manifold heat radiates into the oil and engine coolant. But I think there’s another reason the manifold is shifted outboard – it leaves room for an exhaust catalyst that will probably be required in the future.

This exhaust manifold looks primed for an external catylyst.

This exhaust manifold looks primed for an external catalyst.

At the Miami International Boat Show last February, the subject of outboard catalysts came up during a media briefing hosted by Mercury. The seminar was intended to be an update on the implementation of catalysts on sterndrive and inboard engines. But when someone asked whether cats for outboards were also in the works, the response came from Kevin Grodzki, president of sales, marketing and commercial operations at Merc. He explained that during the summer of 2011 Mercury would be engaged in outboard catalyst testing sanctioned by the California Air Resources Board (CARB), which is contemplating future emissions regulations for outboards. He said that tighter regulation of outboard emissions were “imminent,” perhaps by 2016, and that meeting those regulations could require a catalyst on at least some outboards. He added, however, that outboard emissions are not currently on the agenda of the federal EPA. So this could just be a California issue, although the EPA has a history of following the lead set by CARB.

The testing being conducted by Merc would gauge the effect of emissions-reduction equipment on the performance of the motor, the integrity of such a system, and its potential cost. One big challenge, said Grodzki, will be fitting a catalyst under an outboard cowl. He also said that Merc is taking the industry lead on this project because of its experience with development of sterndrive catalysts.

If exhaust catalysts are “imminent” for outboard motors, it makes sense that Merc would plan ahead to accommodate such a system on a new motor. Of course, when I raised the question at the 150 FourStroke walk-around, all I got in reply was smirks and shrugged shoulders. They don’t want to talk about it right now.