Probably the hardest part of any engine swap is the wiring, especially if you are running EFI and want the original computer to run the newer engine. For project UglyTruck (a 2000 Silverado) I'm swapping from a 5.3 LS to an 8.1 Vortec big block.

While many consider the 8.1 to be nothing more than a large LS, it actually has quite a few differences. The wiring harness is very similar, and both engines can be controlled by the same computer, but there are several connections which need to be modified and moved around to make it all work together. This time we'll go over the differences between the two powerplants, and how I had to move things to work. But at the end of the day, it fired up, and sounds amazing!