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Testing Four Of The Most Popular LS Intake Manifolds On The Dyno

Whether you are a fan of the Bowtie or not, there is no denying that the LS platform has some of the strongest aftermarket support of any platform, ever. With Holley Performance leading the way and creating a plethora of intake manifold options for the platform, the team realized that with all the different options now available, it could be confusing as to how each different iteration performs.

So, using a 440 cubic-inch LS engine (we covered the short-block build here, and we’ll have the long-block article up soon), Holley went to Westech Performance Group to test out four of the most popular LS intake manifolds they make. With Holley’s Mark Gearhart and Westech’s Steve Brule analyzing the results, it comes down to way more than just peak power numbers, as they point out.

Now just to be clear, three of the four intakes tested all use the same Hi-Ram lower intake. The particular lower intake manifold used in the test has been ported to match the cylinder heads by Brett Barber of Air Flow Solutions. Besides making a convenient test methodology, it also shows the versatility of Holley’s Hi-Ram intake manifolds.

One thing to keep in mind with the absolute numbers presented on this dyno graph is that this engine is a pretty stout combination. However, it will still decently illustrate the differences between the different models of manifolds.

Dual 4500 Throttle Body Hi-Ram

“[The dual 4500 throttle body configuration] was obviously the winner,” says Gearhart. He says “obviously” because this is the combination with the most intake flow. Each of the 4500 throttle bodies is rated at 2,000 cfm for a whopping 4,000 cfm of airflow available. The combination topped the charts, making 754 horsepower and 624 lb-ft of torque.

“The math says this combination is supposed to use about 1,000 cfm of intake flow,” explains Brule. “There’s about three or four times that much on here right now. So I think the results we saw, where there is a slight divergence in the curve over the 4150s might be as much related to bore-spacing [of the throttle body] with the bores being a little better aligned over the ports.”

It shouldn’t really come as a surprise that the dual 4500 throttle body setup provided the peak horsepower and torque numbers in the test. With 4,000 cfm of airflow from eight 2.25-inch throttle blades, the engine has a very narrow throttle response range, and drivability will likely suffer with this combination.

Of course, this test is about more than peak power, and Brule addresses that fact head-on, saying “You might pick up 4 or 5 horsepower on the top end, but the sacrifices you make on drivability isn’t generally worth it.” He points out that, while the response of the bigger throttle bodies might feel snappier, at a certain point in the throttle opening, you stop seeing gains, since the engine is already ingesting as much air as it can.

“In a drag race application, this is fine. If you were to try and drive this combination on the street, there is a lot of surface area [of the throttle bores] that is available and opens all at once. That’s going to make it pretty touchy to drive,” Brule concludes of the dual 4500 configuration.

Dual 4150 Throttle Body Hi-Ram

The smaller dual 4150 throttle bodies are rated at half the airflow of the 4500s (1,000cfm vs 2,000cfm) but still performed quite well in this test. The dual 4150 setup netter 747.7 horsepower and 621.1 lb-ft of torque. If you look at the curve, it is almost a trace of the 4500 curve, with a slight separation on the bottom and top ends. “That proves the fact that we don’t really need as much airflow as the 4500s could deliver,” says Gearhart.

“It’s interesting; when we start talking about acceleration rates of the engine, and how you need airspeed to make the carburetor work, the fuel injection isn’t going to be as sensitive to that,” Brule explains. “The throttle size isn’t going to change the way the engine accelerates a whole lot. It just has the potential to make the engine touchy [if you go too big]. I’d choose the dual 4150 setup if it were a street car, but I might choose the 4500s for a drag car, because they look so cool.”

With a total of 2,000 cubic feet per minute of airflow available, the dual 4150 throttle body configuration offered more than enough air to the engine. If this is the setup you are looking for, the slightly reduced peak numbers are worth it for the increase in drivability over the dual 4500 setup.

Single 105mm Forward Facing Throttle Body Hi-Ram

The next setup on the list is Holley’s standard forward-facing LS Hi-Ram lid, which is much more traditional looking, when you think of an EFI intake manifold. With it’s integral 105mm throttle body opening, a standard straight-bore 105mm cable-actuated throttle body was used. The combination yielded 732.6 horsepower and 606.5 lb-ft of torque. Looking at the graph, the difference in the peak numbers carried across the entire dyno pull. “That actually surprised me a bit,” Brule says. And surprising Steve Brule with dyno results isn’t an easy feat.

“I think there might be something to do with the shape of that top. There’s less volume with that lid is what I’m kind of seeing — visually, without measuring it. But, I think it is overall less plenum volume, not necessarily the restriction of a 105mm throttle body. That thing still flows a whole bunch of air.”

The most traditional “EFI” lid of the three Hi-Rams tested, the 105mm forward-facing inlet is also available in a 93mm variant, and the throttle bodies are available in both straight and tapered configurations, in order to further increase the drivability of the Hi-Ram.

Gearhart points out that the 105mm throttle body is rated at about 1,500cfm, so about 25-percent less than the dual 4150 throttle bodies, and about 50-percent more than a single 4150 throttle body. In Brule’s mind, there’s almost no doubt that the straight shot provided by the dual quads adds to the equation compared the rotation of the air required by the forward-facing intake. “The better the alignment, the better it is over the port, the more opportunity is there for better cylinder filling.

MSD Atomic Air Force

If you were to look up “apples and oranges,” the Atomic Air Force intake being included in this test would probably pop up. First, the Air Force manifold tested hasn’t been ported at all, so that puts it at a distinct disadvantage. Next is the fact that the runners on the Atomic Air Force are much longer than those of the Hi-Ram. Finally, while not necessarily a performance parameter, the Atomic Air Force manifold is the only polymer intake on the list. However, the Atomic Air Force will also fit under stock hoods.

The peak power numbers of 718.7 horsepower and 621.5 lb-ft of torque placed the manifold about where everyone expected on the list, but then, the radically different design (from the Hi-Ram) did lead to better average power production of 605 horsepower and 579.9 lb-ft, outpacing the 105mm intake’s 598 average horsepower and 570 average lb-ft.

The black sheep of this group, the Atomic Air Force intake manifold was the only polymer, long-runner manifold in the test. We highly suggest you don’t judge the manifold by the peak numbers from the test alone, and instead look a the dyno sheet closely.

“You’ll hear on the internet, that the intake manifold doesn’t matter [in regards to where the power is made in the powerband] if it’s fuel-injected. I see it all the time,” says Brule. “Whether it’s fuel-injected or carbureted, the length of the runner still matters. The beauty of fuel injection is that you can package really long runners in a very low-profile package, because you’re only flowing air, you aren’t flowing fuel. The Atomic has way more drivability, way more torque down low, but you give up some of that top end.”

Really, what it all boils down to when looking at Holley’s line of intake manifolds for the LS engine, is what kind of packaging constraints you have, where you want your powerband to be, what kind of drivability you require from your engine, and finally, what you like the looks of. With the modularity of the Hi-Ram family, and the awesome street manners of the Atomic Air Force, there’s something for everyone.

Here, you can see the comparative powerbands of the four intake manifolds. Of note, look at the red trace is the Atomic Air Force. Notice how it outperforms everything up until about 5,500 rpm. There’s more to the story than just the peak power numbers might suggest.

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About the author

Greg Acosta

Greg has spent fifteen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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