With such a wide array of aftermarket parts available for the LS family of engines, there’s a multitude of ways to get serious power from these engines.
Choosing a combination of performance parts for a build is rarely an exact science, but having a clear idea of where you want to find gains in the power band can help to point you in the right direction, and keeping that in mind when choosing an intake manifold for your motor can have a significant effect on the end result.
We took a recently-built LS3 to Westech Performance and put the mill on the dyno to get baseline numbers with the stock LS3 intake manifold provided by GM Performance, then bolted on three different aftermarket options to see how they stacked up against GM’s own design. Ryne Cunningham from Cunningham Motorsports took up the tuning role to make sure that our stock-style Howell EFI system was adjusted to provide the best possible power output for each of the manifolds we tested.
The test subject we’re using is the LS3 we built for the LS3 Versus Coyote Budget Engine Shootout. We laid out a set of ground rules for the shootout, which included stock or near-stock displacement, natural aspiration, near 11:1 compression, street-friendly hydraulic roller camshafts, factory PCMs, and a budget of $10,000 for parts.
When we selected parts for the build we had two main priorities: high-end power, and durability. Some of the key players in this equation include a factory LSA crankshaft, LS3 CNCed cylinder heads with ported intake runners, and a Comp Cams LSR roller camshaft with .617/.624-inch lift and 281/297-degree duration, which is designed to make power in the 2,000-7,000 rpm rev range. You can read about all the parts we used in this LS3 build here.
It’s important to note that since this engine wasn’t built with a specific intake manifold in mind, it isn’t optimized to take full advantage of manifold designs that differ substantially from the stock piece. Regardless, the dyno tests did allow us to glean some interesting data about how different intake designs can affect the LS3’s power delivery.
Stock LS3 Intake
It wasn’t that long ago that the stock intake manifold was one of the first things a builder would swap out to free up a substantial chunk of power, even for mild street builds. OEMs formerly struggled to manufacture these kinds of components in a way that struck a balance between cost, reliability, and performance, and that provided a lot of room for improvement by turning to the aftermarket for a higher quality piece. But those days are in the past, as evidenced by this stock LS3 manifold. By the aftermarket’s own admission it’s a well-designed piece, delivering a solid balance between low-end grunt and top-end peak output.
Peak output numbers for the stock intake are 556.3 hp at 6,500 rpm and 497.2 lb-ft of torque at 5,500 rpm, with an average of 311.82 horsepower and 430.66 lb-ft from 3000-4500 rpm, and 513.64 hp and 479.83 lb-ft from 4500-6800 rpm. Solid numbers for a relatively mild build put together with street manners and reliability in mind, something GM was likely aiming for when they designed this intake for the LS3.
Of course, this piece has the inherent virtue of fitting like an OEM component because it is one. But despite its admirable showing on the dyno, we can’t help but wonder if there’s more power waiting to be unlocked with an aftermarket design.
The first up from our aftermarket options was LSXr from Fuel Air Spark Technology. Like all FAST manifolds, the LSXr features a modular multi-piece design for easy internal access and a special polymer construction that’s designed to dissipate heat more effectively than aluminum.
“The LSXr has been the best manifold that we’ve tested for street applications,” says Chris Potter of FAST. “Truthfully, the stock LS3 manifold is a fairly decent piece right from the factory, but the LSXr picks up power across the board compared to the stock intake.”
That jives with our dyno test results as well, which show noticeable gains in horsepower and torque throughout most of the rev range, particularly in the mid-range between 4,500-5,500 rpm. Output for the LSXr topped out at 566.3 hp at 6,600 rpm and 515.3 lb-ft of torque, yielding a gain of 10 hp and 18.1 lb-ft of torque over the stock intake, with an average of 316.45 hp and 437.8 lb-ft from 3000-4500 rpm, and 524.35 hp and 489.84 lb-ft from 4500-6800 rpm.
A lot of time was spent optimizing runner length to improve upon the stock intake across the entire operating range of the engine. – Chris Potter, FAST Technology
One of the key benefits of the LSXr’s design is that it will fit within the same envelope as the stock manifold, which means there’s no hood modifications required to swap in the LSXr for the stock piece. Much like the stock manifold, the LSXr’s polymer construction also helps keep weight off of the top of the engine as compared to an aluminum manifold. Incremental weight savings can add up quickly, and shaving off pounds from above the vehicle’s center of gravity will have an affect on not only straight line performance but handling as well.
The LSXr also makes a strong case for itself versus the stock manifold for street use by virtue of the fact that there’s no sacrifice anywhere in the rev range – the LSXr either made nearly-identical power to the stock manifold or more, with peak power coming in at virtually the same point in the power band as stock for both horsepower and torque.
Simply put, an extended runner length helps to build power over a given RPM range. -Blane Burnett, Holley Performance Products
Sporting a modular base that allows it to be used with either EFI or carbureted setups, the Hi-Ram is geared toward fairly stout builds, and the reality is that our budget LS3 is probably on the lower end of the totem pole for this intake’s intended application.
As the graph indicates, the Hi-Ram delivered some impressive gains. Output peaks out at 605.4 at 7,000 rpm while torque is pegged at 496.7 at 6,100 rpm, a gain of 49.1 horsepower and a loss of 0.5 lb-ft of torque, with an average of 301.32 hp and 419.12 lb-ft from 3000-4500 rpm, and 529.08 hp and 479.62 lb-ft from 4500-7100 rpm.
Much of this can be attributed to the unrestricted, higher volume runner design of the Hi-Ram – without a concern for packaging the intake to fit into the stock manifold’s dimensions, the runners can be extended and their path straightened, which in turn improves performance on the top end.
“Simply put, an extended runner length helps to build power over a given RPM range,” says Blane Burnett of Holley Performance Products. “Along with the cross section and taper, the runner length determines where the motor makes power. Ideally, the intake runner length, as well as overall design of the manifold, should be matched with the camshaft timing, cylinder head flow, and even header design to properly fine-tune power production for a given RPM range.”
The third intake in the lineup was the Holley Mid-Rise manifold (PN 300-135). Like the FAST LSXr, the Mid-Rise is a modular design that’s tailored toward street use, with a power band from 1,500-6,500 rpm and a 10.44-inch height that – while taller than the stock manifold and the FAST LSXr – is still suitable for limited hood clearance applications, though it may require an aftermarket cowl induction hood for some vehicle applications.
“Being part of the Holley modular intake line means that this intake is not only available as a complete kit with intake, adapter, 92 mm top and fuel rails, but all parts can also be purchased separately for a custom intake build,” notes Burnett.
Considering this customizability, and in the interest of evening the playing field between the three aftermarket intakes being tested, we opted to use the Hi-Ram’s upper section rather than the Mid-Rise’s stock top.
The reasoning behind the switch is that the Hi-Ram is designed to be matched with the 102 mm size of the Nick Williams throttle body we used to test all the intakes aside from the stock one, and the Mid-Rise’s stock upper section is designed to work with the stock 92 mm throttle body. The mismatch between the size of the intake port opening and the larger throttle body would have likely worked to the Mid-Rise’s detriment, and the tops of the two Holley manifolds are identical aside from the size of the throttle body opening.
Perhaps a testament to the stock LS3 intake manifold design but surprising nonetheless, the Mid-Rise actually lost power versus the OEM piece across nearly the entire rev range, only showing some modest gains over the stock intake at the edge of the top end despite our efforts to match the intake and throttle body port sizes. Peak output with the Mid-Rise intake stands at 555 horsepower at 6,900 rpm and 483.3 lb-ft of torque at 5,700 rpm, losses of 1.3 hp and 13.9 lb-ft, with an average of 308.99 hp and 429.06 lb-ft from 3000-4500 rpm, and 507.03 hp and 465.32 lb-ft from 4500-7000 rpm.
While there’s a multitude of factors at play here, ultimately the Mid-Rise is really designed for a dual quad setup rather than the EFI we’re using here, and we’d speculate that it would also really come alive under boost. However, from a sheer bolt-on perspective on this particular engine build, it’s probably not the most ideal choice, and illustrates the importance of matching your intake to the other components of your build to ensure you’re getting a benefit from the parts you bolt on.
Crunching The Numbers
It’s important to note that this is not a shootout between these intakes – it’s a fact finding mission. In comparing the results between these four options, we get a better idea of the strengths and weaknesses of different designs when applied to a control, and in this particular scenario, that control is a fuel injected, 550 horsepower engine built for street use.
That means that while this LS3 might be able to take advantage of the design of LSXr, that particularly well-matched pairing is to some degree happenstance – if we were using a pair of four barrel carbs or a supercharger, the Mid-Rise might’ve yielded more gains than the FAST intake. And if this engine were built with high-RPM competition in mind, the Hi-Ram likely would have widened its gap on the top end in relation to the other three even further.
As a quick summary, here’s a look at the results of all the intakes we tested:
- Stock LS3 – Peak: 556.3 hp at 6,500 rpm /497.2 lb-ft of torque at 5,500 rpm, Average: 311.82 hp /430.66 lb-ft (3000-4500 rpm), 513.64 hp / 479.83 lb-ft (4500-6800 rpm)
- FAST LSXr – Peak: 566.3 hp @ 6,600 rpm / 515.3 lb-ft @ 5200 rpm (10hp / 18.1 lb-ft gain), Average: 316.45 hp /437.8 lb-ft (3000-4500 rpm), 524.35 hp /489.84 lb-ft (4500-6800 rpm)
- Holley Hi-Ram – Peak: 605.4 hp @ 7,000 / 496.7 lb-ft @ 6,100 rpm (49.1 hp gain, 0.5 lb-ft loss), Average: 301.32 hp / 419.12 lb-ft (3000-4500 rpm), 529.08 hp / 479.62 lb-ft (4500-7100 rpm)
- Holley Mid-Rise – Peak: 555 hp @ 6,900 rpm / 483.3 lb-ft @ 5,700 rpm, (1.3 hp / 13.9 lb-ft loss), Average: 308.99 hp /429.06 lb-ft (3000-4500 rpm), 507.03 hp / 465.32 lb-ft (4500-7000 rpm)
The takeaway here is that it’s important to consider not only how your engine is built, but how it will spend the majority of its time as well, as an intake that sacrifices low-end grunt for gains on the top might be ideal for a racing application but could easily be perceived as a net loss on the butt dyno if the engine is being used on the street the majority of the time. Putting together a clear strategy for your modifications will ensure that you get the most bang for your performance buck.