On almost every modern car, and lawnmower for that matter, internal combustion engines feature an exhaust manifold. It's basically a collection of three, four, or six (or however many cylinders the engine is) tubes which collect exhaust gases directly from the head. These tubes then combine into one in a very small space and feed into the exhaust pipe that you see poking out the back.
This cluster of tubes from the head (manifold) is usually constructed cast iron or other heavy metal (unless it's a sports car or has aftermarket headers), and is mounted externally on the head via bolts. This system has been around since the dawn of the internal combustion engine.
GM has come up with a more compact and efficient design which does away with the old external manifold. It collects all of the four, six or however many cylinders together within the aluminium head cast itself. This means there's no need for a big heavy manifold, just a simple and single dump pipe is used for all of the cylinder's exhaust.
GM says the design improves exhaust flow by up to 10 percent compared with the existing V6 engine, and since catalytic converters can be mounted closer to the engine, they are able to heat up and work effectively sooner compared with those on the old engine. GM says this contributes to a reduction in emissions. A weight saving of up to six kilograms helps improve overall fuel consumption from 8.1L/100km to 7.8L/100km (2011 to 2012 model).
It's good to see the big companies are still looking to improve the somewhat old and traditional engine layouts we've all become used to. GM has since patented the design but it will be interesting to see if this technology takes off.
Take a look at the video below for an explanation of the technology by GM's V6 engineering boss.