Manhandling a tail-happy 10-second beast down the dragstrip? Bring it on! Connecting a few innocuous strands of copper where a wiring schematic says they should go? Run for your life! Indeed, hot rodders have a funny way of looking at things sometimes, and electrical intimidation has burst many bubbles of EFI grandeur. Fortunately, that needn’t be the case anymore. In last month’s installment of “How it Works,” we showed how simple it is to fit an LS engine and late-model trans into your classic Bow Tie ride. With all the pre-fabbed motor mounts, crossmembers, and headers at your disposal these days, dropping a Gen III/IV small-block between your car’s framerails is arguably the easiest part of an LS swap. That said, hooking up the electronics, sorting through the wiring, feeding fuel to the lump, and programming the computer isn’t that much harder.

Thanks to continuing aftermarket innovations, properly wiring up an EFI system is often as simple as connecting four wires. Furthermore, the latest stand-alone computers can literally program themselves. If you’re still not ready to take the EFI plunge, you can even plop a carburetor on an LS small-block and still have it play nice with all the factory sensors. To find out how to feed fuel and spark to a freshly retrofitted LS small-block, we consulted with Rick Anderson of Holley, Jesse Powell of Aeromotive, Damon Sampson of Mast Motorsports, Eric Blakely of Edelbrock, and Mark Campbell of Street and Performance. Equipped with the knowledge provided by our expert panel, the fear of electronics and wiring should never get between you and your aspirations of EFI nirvana.

Stock vs. Aftermarket Computers

Mark Campbell: Using a stock GM computer and wiring harness for an LS swap application can be done, but it takes a bit more effort than using a stand-alone aftermarket system. First off, you need to get a copy of the factory wiring schematics. That way, you can go through it, label every wire, and determine which wires are needed and which ones aren’t. The biggest challenge is programming the computer. You can either send it off to a tuner to set it up for your engine combination, rearend gear ratio, and tire size; you can also purchase tuning software from one of several vendors, and try to tune it yourself. Before you can even fire up the motor for the first time, you have to disable the vehicle antitheft system that’s programmed into the computer. Over the years, GM has used several different computers in LS applications, and not all of them are compatible with various model-year motors. Up until 2005, GM used 24-tooth crankshaft reluctor wheels on Gen III small-blocks, so if you have an earlier LS motor, you’ll need to match it up with an ’05-and-earlier computer. Starting in 2006 in Corvettes and 2007 in trucks, GM switched to 58-tooth crankshaft reluctor wheels in the Gen IV small-block. To run these motors, you need a computer out of a ’06-and-later car or a ’07-and-later truck. While the ’05-and-earlier computers are compatible with both drive-by-cable and drive-by-wire throttle bodies, the newer Gen IV computers will only work in drive-by-wire applications.