The E3 introduced the 567 series engine, which would power all later E units, the 567 being a mechanically aspirated two stroke 45 degree V-type with displacement per cylinder, a total of per engine. Models E3 through E9 used the EMD model 567 engine, named after its engine displacement in cubic inches per cylinder. The 567 model had been developed by EMD specifically for locomotive use, and exhibited excellent performance and reliability in high speed passenger train service. The 567 had a greater displacement per cylinder than the 201-A and ran at a higher maximum rpm, elements which when combined gave greater engine output. The 12V-567 V12 model used in the E3 through E6 developed 1000 hp (750 kW). The E7 model used the 12V-567A rated at 1000 hp (750 kW). The E8 used the more advanced 567B unit, with improved exhaust manifolds and other enhancements to give 1,125 hp each. More development resulted in the 1200 hp (900 kW) 567C engine used in the E9.