The exhaust emissions of the 6V-71E and 6V-71N engines, used in transit coaches, are compared to illustrate that design revisions can affect diesel exhaust. Carbon monoxide and sulfur dioxide are discussed and the effect of design revisions on aldehydes, oxides of nitrogen, and hydrocarbons are illustrated. The effects of the design revisions on exhaust smoke and odor are compared using three different measurement techniques. Smoke is compared using a filtering meter on engine dynamometer tests, a sampling light extinction meter on road tests, and a full flow light extinction meter on chassis dynamometer tests. Odor is compared using a sniff-box technique and a psychological scale, a threshold technique using natural dilution in a large building, and a sniff tube-dilution technique using the Turk bottle rating.