Mahle pistons for the early 3.9L Cummins engine aka the 4bt. These pistons are for the 89-93 models. This is a complete piston set which comes with, Pistons, rings, wrist pins, and clips. We use Mahle pistons on all of our engine builds. These pistons come with a ceramic coated top and teflon coated skirts. The coating on the pistons helps to disperse heat and improve lubricity between the piston and cylinder walls. The pistons have also been champfered so when the piston does expand under heat it will not grab the cylinder wall.