Performance Roadblocks For The 5.3 LS V8: Stepping Up From Stock Power
The 5.3-liter LS engine is perhaps the most commonly swapped member of GM's Gen III and Gen IV family of V8s. Found in millions of pickups, vans, and SUVs, the sheer ubiquity of this LS V8 guarantees its popularity, as it's easy to find donor vehicles and the aftermarket has rushed to support the 5.3 with a huge volume of inexpensive parts.
A large number of 5.3 swaps make use of the Gen III LM7 engine, which offered between 270 and 295 hp and was sold from 1999 to 2007 across a wide range of Chevrolets and GMCs. Factory torque checked in as high as 335 lb-ft or as low as 315 lb-ft.
There are, of course, a number of early 5.3-liter LS variants, including the flex-fuel L59 and the rare aluminum block LM4 and L33 versions. The Gen III 5.3-liter was replaced by the Gen IV in 2008, with the LY5, LH8, LMG, and aluminum-block LH6 and LC9 versions of the motor offering between 300 and 320 horsepower and bumping max torque to 340 lb-ft.
Both the Gen II and Gen IV engines provide a healthy starting point for anyone seeking a well-performing V8. In particular, the heads on these motors flow far better than the stockers on the small block Chevy motors that preceded them. and you're looking at a ceiling of 400 to 450 horsepower supported by the factory intake and heads before you'll see much benefit from an upgrade. The standard exhaust manifolds on the truck motors are also fairly non-restrictive.
That being said, there are a few key areas where the LS platform responds exceptionally once you take down the roadblocks keeping them from achieving their maximum performance.
Performance Roadblock #1: Camshaft
Given that almost every 5.3 LS was installed under the hood of a truck, it's perhaps no surprise that their factory camshaft (191 degrees at 0.050-inch lift in the LM7) is designed to balance power and fuel economy and favor low-rpm torque. Gen IV engines moved to somewhat more aggressive cam profiles (196 degrees in the LY5, for example), but still oriented towards task-focused towing and daily driving above all else.
Would it surprise you to find out that it's possible to achieve a dramatic boost in power with a simple cam swap—especially if you're willing to shift output to the higher end of the rev range? Cam specs are a complicated topic, but in general, moving to a 215 degree cam will add as much as 50 horsepower to the humble LM7, and you can double that by stepping up to the 240 degree range.
It's important to understand what you'll be sacrificing by installing a hotter cam. Once you're at 230 degrees duration, you'll definitely notice a lope at idle, and you'll also lose out on intake vacuum as well as that juicy low-end torque that the original truck-focused grind was so good at generating. If you're building a drag car, that might not matter much to you, but on the street a more modest cam with better manners could be a better idea.
If your 5.3 is in a truck, then you'll want to find a compromise cam that doesn't require you to rev past 5,000 rpm to touch the extra horsepower its generating. There are many truck-specific cam options out there for the 5.3 that will offer a meaningful boost of power (between 60 and 75 horses) without transforming the engine into a screamer.
Finally, keep in mind what modifications you'll need to make to support cams with higher valve lifts. If lift is 0.500 inches or less, you'll likely be fine with stock hardware in the valvetrain, but at 0.550 inches or higher you'll want to install heavier duty, or even dual valve springs. The trunion bearings on the stock LM7 rocker arms are also a known weak spot, and can be replaced entirely or upgraded, and with a new cam you'll want to install equally new lifters.
Performance Roadblock #2: Fuel Injectors
At the low end of the 5.3 spectrum, the LM7's 25 lb fuel injectors are going to max out before they reach the 400 horsepower stage, typically around the 380 horse mark. Gen IV injectors, particularly those on flex fuel models, are at or just above the 30 lb mark, which will bring you closer to 400 horses. Once you're reaching into the 500 horsepower plateau, you'll most likely be looking at a 42 lb injector for a naturally-aspirated engine.
Installing higher capacity injectors means you'll need to retune your ECU accordingly, but if you've installed a more aggressive camshaft you're likely already looking at a reflash. Don't worry about the fuel pump on a Gen IV—you're good to nearly 500 horses with the stock unit.
Performance Roadblock #3: Intake
We've established that the stock truck intake on the 5.3 LS is a good one and should do the job until nearly the 500 horsepower mark, but that doesn't mean it's going to fit your project. Taller than what one would find on a passenger car LS setup, you could run into hood clearance issues that will require swapping in something different.
The stock throttle body on the LM7 intake is 78 mm, and the long intake runners on truck motors are intended to service the needs of low end torque delivery. If you want to maintain a truck-like power band the factory intake from the Chevrolet Trailblazer SS will deliver roughly 10 extra horses and give you a 90 mm throttle body without sacrificing low-end grunt.
If you're more interested in high end power, there are intakes out there from F.A.S.T that accommodate larger throttle bodies while adding roughly 25 ponies, as well as tunnel ram designs that are good for roughly 30 percent more. Take care to match your intake with the goals of your build, and take into account whether you'll be using any power adders like nitrous or forced induction.
Performance Roadblock #4 Gen IV AFM and VVT Delete
Many Gen IV engines came with more sophisticated fuel management technologies than the Gen III. Specifically, Active Fuel Management (AFM), which shuts down a bank of cylinders during steady state cruising in order to improve economy, and variable-valve timing (VVT), which works to better balance power and fuel consumption.
While these systems were effective when they left the factory, they can pose a problem for anyone looking to build a Gen IV engine. AFM lifters are a known failure point for the LS, and while it can be disabled via an ECU tune or device plugged in to the OBD-II port, it's a much better idea to install an AFM delete kit that replaces the troublesome lifters (and comes with a new valley cover). You'll have to replace the camshaft at the same time (because the stock unit features two lobe profiles), which makes it the perfect excuse to upgrade. Finally, you'll have to tune out the AFM function from the ECU.
VVT is less troublesome for street cars, but if you're doing a major build on a vehicle intended for track use there's no advantage to maintaining variable-valve timing. More aggressive cams can cause problems without very careful engine programming and phaser limiting. Deleting the system requires a new upper timing gear as well as a non-VVT camshaft and an ECU tune.
Want to learn more about the LS family of V8 engines? Check out our complete guide to Gen III and Gen IV LS motors.