Caterham use exclusively four cylinder engines in their cars.  These range from the Honda blackbird motorcycle engine, to the Rover K-series 1.8 litre VVC.  

The intake manifold is 'painted' red, with a large capacity air filter.  The exhaust exits through the side of the chassis, to a side mounted silencer.

In the second photo, the micro-motor powering the windscreen wipers can be seen.  It is sited in between the chassis rails on the left of the vehicle.

Also visible is the steering linkage, running along the right side of the engine, and the front end of the transmission.