The Performance Design XS Intake Manifold Does What Others Don’t

Since the release of the Gen-IV LS3 back in 2008, the aftermarket industry has been trying to design an intake manifold that is better than the OEM LS3 intake. We know the term “better” can mean different things. However, GM did such a good job when creating the LS3 intake that most of the aftermarket replacements simply move the horsepower and torque curves up in the RPM range. In terms of gains in horsepower or torque, aftermarket intake designs typically sacrifice one to improve the other. So when Jason Harding of Performance Design told us their new XS intake manifold produced gains in both horsepower and torque across the board they had our attention.

XS intake

The XS intake manifold from Performance Design breaks the mold of conventional thinking for how an intake makes power.

Performance Design is best known for its beautiful intake manifold creations that blend aluminum and carbon fiber into a component that is a high-performance work of art. These intake manifolds offer high-end performance that comes with a price point that can be out of reach for the average enthusiast who wants to change the look of their engine while improving performance. To solve this, the team at Performance Design started with a clean slate to design a completely new intake manifold. This new design needed to meet three goals — it had to outperform the OEM LS3 intake in all areas, it needed to be at a price that was affordable to the masses of LS enthusiasts, and it needed to fit under the factory hood of C6 Corvettes and fifth-gen Camaros; more on that in a bit. What they came up with is the XS LS3 intake manifold, and it’s quite a departure from what Performance Design has done in the past.

Starting From Scratch

When it came to designing an all-new intake manifold, Caleb Newman and the team at Performance Design recognized that many of the high-performance offerings on the market are mid- and high-rise manifolds that do not fit under the factory hood and cowl area of the C6 Corvette and fifth-gen Camaro. Even several of the current intake manifolds offered by Performance Design are too tall for these cars with factory hoods, as well as many other vehicles that are home to LS swaps. With packaging and the overall footprint of the intake manifold a focus of the design, Newman stepped outside the box and decided to bring everything inside the intake plenum. By making the plenum much larger, not only did he realize the benefits of more plenum volume, but the fuel rails, fuel crossover, and fuel injectors could all be placed inside it. Additionally, the intake runners could be lengthened while remaining inside the plenum, without adding any height to the manifold.

The large plenum design allowed the engineers at Performance Design to tailor the length of each intake runner for optimized performance in each of the engine's cylinders.

“We tested three different lengths of intake runners during the development of the XS intake manifold and found that utilizing a mix of the three lengths among the cylinders produced the best performance,” Harding explains. “Most LS3 under-hood intake manifolds simply move the powerband and trade torque for power. We wanted to design something that made power without sacrificing torque and even increasing it.” During in-house testing of the XS intake Newman and the team saw gains of 8 to 10 horsepower and torque on a bone stock LS3.  Their results showed the torque gains to be off peak, flattening the torque curve. Of course, all engine combinations are different and results may vary, and we wanted to get our hands on this intake to try it out for ourselves. Lucky for us, our good friend Tommy Keeter at KPE Racing had an LS3 engine already on his dyno and invited us to come test the XS intake on it as he was keen to see if the unique design would perform as claimed.   

XS Intake

With two throttle body opening sizes available, we chose the 112mm version. It looks huge when compared to the 90mm throttle body on the stock LS3 intake manifold we tested.

The XS intake manifold is offered in two variations. One that accepts a 90mm or 103mm throttle body, and one that accepts a larger 112mm throttle body. We opted for the 112mm version because we planned to test the intake on an LS3 that was not entirely stock. With the XS intake and 112mm throttle body in hand, the first thing to do is separate the top from the lower half. With the top out of the way, we can see how Performance Design packed everything inside the XS intake. 

There are billet aluminum fuel rails included in the XS manifold as well as a hardware kit that has the fuel crossover, fuel feed line stub, fuel rail end plugs, and necessary bolts for installation. An interesting feature of note is the gasket that seals the upper and lower halves. It incorporates a pass-through for the included fuel feed stub we installed on the fuel rail. The fuel feed stub allows for easy connection to factory-style fuel systems. The fuel rails will work with LS3/LS7 factory injectors or aftermarket EV6-style injectors if you need more fuel. Additionally, injector harness extensions are preinstalled in the intake and pass through the plenum wall via pressure-resistant grommets. According to Harding, the XS intake manifold can handle 20 psi if customers choose to add a little boost to their LS3.

XS intake

The yellow plug (not included in the kit) is removed and the fuel line stub is threaded into the fuel rail. It passes through the gasket to the exterior of the intake manifold. Although we tested the engine naturally aspirated, we would like to see how well the intake remains sealed with boost.

Putting The XS LS3 Intake To The Test

When installing the injectors, I highly recommend following the instructions to the letter. Because space is limited, if you don’t position the injectors and injector harness extensions exactly how they are described in the instructions, you will likely find yourself removing the fuel rail and injectors to start over. Once we had our injectors and fuel rails in and bolted down, we installed the MAP sensor in the factory location and were ready to bolt the XS intake to our test engine. Performance Design includes stainless-steel hardware for installation, which makes getting the manifold bolted down a quick process with the use of a swivel socket attachment and a short extension.

With the intake bolted to the engine we connected the injector harness and tested for fuel leaks.

With the XS intake lower half on the engine, we connected the injector harness to test for any fuel leaks before attaching the upper half of the intake to seal things up and prepare to make some power. On the engine, the XS intake looks drastically different than any other intake manifold, while still having an almost factory appearance. The carbon fiber strip that covers the center bolts is a nice touch.

The XS intake manifold looks right at home on our LS3 engine. The routing of the injector wiring harness is a bit tight between the intake and the valve covers, but the injector harness extensions included in the intake ensure no wires are stretched.

Our test engine is a 6.2-liter LS3 with a cam swap and a 90mm throttle body. It’s running stock LS3 cylinder heads and a stock intake manifold for the baseline performance numbers. After the initial pulls, our best results were 565 horsepower and 591 lb-ft of torque.

With the intake installation complete we were ready to make our test pulls on the engine dyno. It was surprising how well the intake performed with no changes to the tune.

The Proof Is On The Dyno

With the XS intake installed and the engine completely cooled down, we fired it up and made several pulls to see if Performance Design’s claimed gains were accurate. Our test engine picked up 37 horsepower for a total of 602 horsepower at the crankshaft. Additionally, torque output increased to 618 lb-ft for a gain of 27 lb-ft of torque. Looking at the dyno graphs the XS intake makes peak horsepower and torque at almost the same RPM as the stock intake and smaller throttlebody. As we mentioned before, typically to gain horsepower with an intake manifold torque is sacrificed. To see the XS intake produce gains in both outputs across the entire RPM range is a testament to its design and the development efforts of the team at Performance Design. 

We ran the engine with the existing tune to see what the XS intake could do with as few changes as possible to the base setup. The performance gains we saw in our testing were achieved with the same tune the engine had with the stock intake and a smaller throttle body.  Of course, we could command a leaner air/fuel ratio and adjust the timing to gain even more power. If we were to put this engine into a vehicle, we would likely make those tuning adjustments once the engine was in the car and on a chassis dyno.

In the image on the left we've highlighted the peak horsepower gain, while the image on the right has the peak torque increase selected. It's impressive to see the XS intake increased both across the rpm range from start to finish.

For enthusiasts wanting to increase horsepower and torque, the XS intake manifold does everything the team at Performance Design told us it would do. Its MSRP of $999.99 makes it a great choice that gives your engine a boost in performance and looks without breaking the bank. For additional information and to order the XS intake visit the Performance Design site. 

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Jeremy Nichols

Jeremy loves to go fast, whether that's on two wheels, four wheels, or boating. With a willingness to compete at almost anything, Jeremy shoots competition long-range rifles matches and races road bicycles and enjoys building vehicles for people.
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