The original run of the Jaguar E-Type, known as the Series 1, are some of the most desirable E-Types. They are notable for their evolution throughout their production run. Early cars (1961-1964) featured a 3.8L engine and partial synchromesh transmission, while later models features an 4.2L engine as well as a full synchromesh transmission. These later models are noted for having a greater drive-ability, while still maintaining the signature style of the Series 1. As Series 1 cars approached the end of their run, certain changes featured in the future Series 2 began to be implemented, resulting in an unofficial "Series 1.5" moniker. These cars featured many of the changes necessitated by the U.S. market. Most of these changes are subtle changes to the running gear and chassis, the most notable being a de-tuning of the engine. The largest visual difference between the Series 1 and "Series 1.5" is the removal of the headlamp covers.