At left is a TJ Rubicon's 4.0L MPI engine backed by an overdrive transmission. At right is an '87 AMC/Jeep 2.5L TBI four. Both engines lack the low-end torque of the 4.2L six that powered the AMC era CJs and the YJ Wrangler through 1990. They need lower (numerically higher) axle ratios to perform well. While there is some room for improving these EFI engines, greater mileage will come from gearing changes.