First Look: Performance Design’s XS Intake Manifold for the LS3 V

May 27, 2023

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A stock LS3 rec-port intake manifold is hard to beat and only costs $299. When Chevy went back to the drawing board after the success of the cathedral-port Gen III LS1 small-block V-8, it realized that its new rectangle-port LS3 cylinder head for the Gen IV LS needed a world-class intake manifold to match. That was in 2008, and ever since then the performance aftermarket has been throwing the proverbial spaghetti on the wall hoping it will stick. Through no fault of its own, the aftermarket had no choice but to focus on shifting power and torque to the upper range; the balance between the LS3 intake's low-speed grunt and high-revving horsepower seemed to be nearly perfect. Back in 2018, HOT ROD's Richard Holdener conducted an expansive dyno test of all available rec-port LS intakes on a mostly stock LS3 equipped with just headers and a mild cam (231/247 degrees at .050, .617/.624-inch lift, 113 LSA) and the results threw cold water on all but the most radical high-rpm track applications.

Make no mistake, the aftermarket is both smart and strong, so this left us wondering, can the stock LS3 intake really be that good? With its runners maximized for operation in precisely the range hot-rodders need, the only way to make the LS3's intake any better appears to be approaching it from a clean sheet of paper. Performance Design of Auburn Hills, Michigan, thinks its new XS intake manifold for the LS3 is just that. With the company's soon-to-be-released XS intake, the idea was to think outside the box—or more accurately, to make the box bigger—but we're getting ahead of ourselves. Performance Design has risen to the top of the Chevy LS engine technology pile by bringing some of the most beautiful and functional intake manifolds to market with an artful fusion of metal-crafting and carbon-fiber layup. Performance Design's intake manifolds are as functional as they are attractive, but for ordinary hot-rodding thousand-aires they're normally out of reach. Performance Design's forthcoming XS intake—at a projected MSRP of $999.99—changes that.

Through its affiliation with manufacturer and Tier-1 supplier MPI—the parent company of NylonMold—Performance Design has departed from its traditional use of carbon-fiber and embraced the same technology used for the OE LS3 intake. This nylon-injection-mold technology brings the cost down substantially while unlocking some CFD design tools that help reimagine the intake's architecture—making the box bigger, as we said earlier.

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Injection-molded nylon is hugely flexible as well as inexpensive. (Tooling costs are much higher but are offset by a lower unit cost compared to aluminum when larger production quantities are considered.) A look under the hood of the XS intake (above) shows just how clever Performance Design was in reimagining the LS3 intake. By enclosing the fuel injectors, fuel rails, and fuel crossover within the intake plenum the runners can be longer, as their length is no longer limited by the fuel system's imposing real estate.

The Performance Design XS intake is made of three major parts: a bottom half that mates to the cylinder heads, the eight velocity runners that feed each cylinder and that are housed in the intake manifold plenum volume (shown above), and a lid that bolts to the base and seals the plenum and runners from the outside. It is the internal velocity runners that make the big difference here, as they are much longer than those in the OE and aftermarket LS3 intake manifolds—their lengths have traditionally been limited by the ever-present fuel rails, fuel injectors, and attendant control wiring.

In developing the XS intake, Performance Design tested three different runner lengths ("A," "B," and "C") and discovered that using all three mixed between the cylinders offered the best overall performance. The result is a power curve that, according to Performance Design, boosts output everywhere. The company states that on a completely stock LS3 rec-port engine the XS intake is worth 8 to 10 numbers (both torque and horsepower) over a stock baseline across the entire usable torque/power band—something no aftermarket LS3 intake has ever promised or delivered. The company also states that adding a bigger cam, better cylinder heads, boost, and a free-flowing exhaust only accentuates those gains across the power band. We'll know for sure when our test unit arrives!

With the top shell removed from the XS intake a few things become obvious. The first is the included fuel crossover that connects the left- and right-side fuel rails. Rather than route this on the intake's exterior like other LS intakes, it's inside the plenum where it's been pre-assembled to a new pair of Performance Design fuel rails (also included). Users will opt to either swap in their original LS3 injectors or upgrade to a set of EV6-style injectors (not included). You can also see a series of support stands along the intake centerline for through-bolts that hold the center of the lid to the base. According to Performance Design, these fasteners (as well as additional bolts along the periphery) allow the XS to safely withstand up to 6 bars of internal pressure (86 psi) for use in boosted applications.

Another breakthrough in the Performance Design XS manifold is its unique elastomer gasket that is sandwiched between the intake's upper and lower halves. The gasket is like other sealing regimes in OE nylon-injected intake manifolds, except that it additionally incorporates a pass-through for the included fuel feed stub, which can be seen in the photo above. The fuel feed stub connects to the stock OE-style quick-disconnect junction for easy use with your stock-style fuel system. Performance Design has also included the injector harness pigtail extensions that connect the eight injectors inside the manifold to the fuel-injection harness on the engine. These, like the fuel rail stub, pass through the wall of the intake manifold plenum and are sealed against vacuum and pressure at the plenum wall by pressure-resistant grommets.

As a company well-versed in the unique and sometimes odd air-inlet path demands of bespoke low-production vehicles, Performance Design is situationally aware that LS3 swaps can pose unique installation problems in cars not originally equipped with the V-8. To that end, the company offers a couple of throttle body choices, including provision for 90-103mm-diameter throttle bodies and larger 112mm throttle bodies. Moreover, the intake manifold is designed such that it can be attached to the engine 180-degrees reversed, with the throttle body facing rearward. The XS intake uses the factory MAP sensor location and retains the OE PCV and canister purge solenoid connections. Stainless-steel hardware is included for installation and the XS intake comes with a snap-on carbon-fiber cover to hide the lid's center-spine attachment bolts.

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