The Cummins ISL is a straight-6 diesel engine designed and produced by Cummins. It is 8.9 liters in displacement, and went into production in 1998. The engine was based on its 8.3 liter predecessor, the Cummins C8.3 engine. The Cummins ISL also has a sister engine which is based on the existing ISL 8.9-liter block which runs on compressed natural gas called the L Gas Plus.