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The catalyser secrets of S&S’s road-legal system

Building a performance exhaust used to be a breeze undertaken by everyone from cowboys to wizards. But building one today, in accordance with the latest emissions regulations, is very different indeed.

The core principles haven’t really changed – get the gases out quicker so you can get fresh charge in sooner – but it’s no longer the unfettered wild west it once was. These days, unless you want a bike that fails an MoT or requires the OEM pipe refitting, an aftermarket pipe has to be just as clean as the massive hunk of metal your bike arrives with. So how do they do it? Well, it’s quite simple when you know how.

First principles

First, you have to look at how a standard exhaust works. In your typical bike exhaust there’s a set of header pipes that lead away from the engine down to a catalytic converter. The cat is filled with a honeycomb of ceramic coated with precious metal catalysts that convert harmful gases into safe ones. A typical three-way catalytic converter turns nitrogen oxide into nitrogen and oxygen, turns carbon monoxide into carbon dioxide and turns unburnt fuel into carbon dioxide and water. The downside to this is the inside of a typical cat is incredibly dense to give the catalyst enough surface area to help the reaction take place. Not only does this

‘Automotive aftermarket did it years ago...’

slow down the exit speed of the exhaust gases, which reduces performance and noise, it also weighs a ton. Thankfully though, there’s now a way forward.

Moving on

In a set of pipes like the ‘Grand National 2:2’ for the Indian FTR 1200, exhaust makers S&S use a pair of high-flow catalytic converters that replace the huge box under the swingarm. “The automotive aftermarket figured this out years ago and the two-wheeled space is just getting their head around it, led in a large way by our emissions lab,” says Martin Szlagowski at S&S. “Cat shape, length and chemical coatings are infinitely editable as well as location within the exhaust system. Performance gains are had in part by changing the location of the cat, opening up the honeycomb to allow more efficient exhaust flow and changing the mix of the reactive chemicals.

“Why doesn’t the factory do that? Cost and manufacturing complexity are generally the barrier for an OE. They also work to a price point on each component of the bike, whereas we can take a part and build what the factory could only dream of. In this example, the S&S Cycle Grand National high pipe for the FTR1200 picks up on the styling of the race bikes as well as the concept bike Indian shared last season to create an exhaust few OEM’s would dare build.”