By comparison , the 180 ° flat-6 boxer engine is only moderately wider than the 120 ° V6 , and unlike the V6 is a fully balanced configuration with no vibration problems , so it is more commonly used in aircraft and in sports\/luxury cars where space is not a constraint and smoothness is important .
The flat-6 boxer engine ( 180 ° ) is only slightly wider than the 120 ° V6 , and it is fully balanced .