According to data posted by Ward's Auto, the V8 engine powered a mere 20.8 percent of the total North American light-vehicle output in 2010, down from the 22.8 percent in 2009. In contrast, the four-cylinder engine powered 64.5 percent of all cars built in 2010, an increase from the 61.9 percent in 2009. Ward's chalks up the rising popularity of the once-lowly four-banger to technical improvements, such as direct injection, turbocharging and variable valve timing systems, that have transformed some four-cylinder engines into potent mills that consume significantly less fuel than many V6 and V8 engines.
[Source: Ward's Auto – sub. req.]