It seems like FiTech’s Ultimate LS kits will be a best bet both for anyone doing an LSX swap into a car or building a new engine from scratch. That’s because it includes FiTech’s self-contained engine control unit that is self-learning and also quite customizable. FiTech also packs in a custom wiring harness that includes all the fittings you need and none of what you don’t. That’s actually a big deal because in our experience it’s not the mechanicals that trips up most people doing LS engine swaps, it’s the confusing task of modifying a stock wiring harness that can leave you pulling your hair out.
In addition to the ECU and wiring harness, there are a number of options to choose from depending on what you need. For a stroker LS1 build we have going together, we went with a nearly complete kit that also includes a long-runner fabricated intake, big 102mm throttle body, fuel injectors, fuel rails, fuel pressure regulator, handheld controller, fuel pump, coils, and a ton of sensors, connectors, fittings, and everything else needed to get it all working. As a system, our kit is designed to be able to handle up to 750 hp.
Of course, a one-size-fits-all solution never works for everyone, so FiTech has several different part numbers with variations on the kit. For example, we chose the long-runner intake to help generate lots of low-end torque, but if hood fitment is an issue you can go with a short-runner intake that’s just 6.5 inches tall. You can drop the coils if you already have your own; go with a kit designed for a maximum of 500 hp, which should work better with a stock 4.8- or 5.3L engine, or even add in an integrated electronic transmission controller.
What we really liked is all the components have already been scienced out as a package so you can be confident everything fits and works well together. That eliminates all the head-scratching that often comes from mixing and matching components from different manufacturers. Plus, that fabricated aluminum intake manifold just looks sweet. Obviously, looks are not a primary consideration when it comes to an engine build, but let’s not pretend that looks don’t matter at least a little bit. After all, everybody wants a little eye candy when they pop the hood with your friends standing around.
We’re sure you are ready to get to it, so we won’t waste more time yapping. Follow along as we assemble one of FiTech’s Ultimate LS kits on a big-inch stroker build and then put it to the test on an engine dyno.
FiTech’s Ultimate LS kit includes everything you need on the induction side to finish practically any (from a stock 4.8 to our big-inch stroker) LSX long-block. This kit definitely passes the eyeball test with its good looks, but we plan to put it to the test on the dyno. This is a fresh build, but we’re betting the Ultimate LS kit will also be a big help for anyone looking to swap an LSX engine into a car that never came with one.
Here’s the specific FiTech Ultimate LS kit we are using. As you can see, it’s pretty comprehensive with an intake, big 102mm throttle body, computer, handheld touch-screen controller, fuel pressure regulator, injectors, fuel rails, braided crossover line, fuel pump, coils, and a wiring harness. Not pictured are several included sensors and a lot of brackets and other assorted hardware.
We decided to put the 750hp kit to the test on a big-inch stroker LS build, although we expect most users of the FiTech Ultimate LS kit will be using it to help simplify LS swaps. The block is a 6.0L iron LQ9 we pulled out of a Cadillac Escalade in a junkyard, but it has been fully machined at Automotive Specialists with the bores punched out to 4.070 inches.
On the dyno, the FiTech system had the engine fired up and running smoothly surprisingly quickly. We tried a few different changes with the air/fuel ratio and some other things, but, generally, we allowed the self-learning ECU to run the show. As you can see, we had the serpentine belt off and an electric water pump moving coolant through the engine. We also didn’t use a velocity stack on the intake, but we did have a hood (not shown in this photo) blowing fresh air into the intake. We saw peaks of 521.2 lb-ft of torque at 5,300 rpm and 597.3 hp at 6,700. We were dying to break the 600hp mark, but the engine just didn’t want to do it and we weren’t willing to get into cheesy magazine fakery to get there. Peak numbers are nice for bragging rights, but they really don’t tell you how much fun a car is going to be to drive. What we are really stoked about is the power across the range. From 4,500 to 7,300 rpm we averaged a very impressive 486.4 lb-ft of torque and 486.39 hp while burning pump gas!

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