GM’s LS engine has spawned an entire industry full of high performance engine parts designed specifically to add to this engine’s formidable power promise. Holley is right there with a vast collection of intake manifolds. The selection is broad enough that it demands we run through all the cast aluminum versions in order to sort out all the different applications. There are, of course, other intakes available through Holley for these engines such as the affordable Sniper fabricated manifolds. We’ll save those for separate attention at a later date but for this story we’ll concentrate on the cast aluminum LS intakes.

Let’s start by differentiating the carbureted manifolds from the EFI versions. While all production LS engines have always been digitally controlled, many hot rodders still prefer to run a nice traditional big Holley carburetor paired with an MSD ignition conversion so we’ll separate the carbureted versions from their EFI counterparts.

As most of you are likely aware, there are three LS cylinder head configurations for the port fuel injected Gen III/IV engines. The original Gen III engines came with what have come to be called cathedral port heads since the tapered upper portion of the port looks like a steeple. Later, as displacement and horsepower demands increased, the Gen IV engines expanded into a larger, rectangle port configuration. So when looking at intakes, you need to know which heads you have in order to make the right choice. The third choice is the LS7 which requires its own specific intake manifold bolt pattern.

Finally, the change to direct injection created the Gen V version LT engine with yet a fourth intake pattern iteration. Not too surprisingly, these bolt patterns and port configurations do not interchange. So if you have an engine with cathedral port heads, it will require a manifold that is designed specifically for cathedral ports. And while the LS7 appears to be the same as the LS3/L92 rectangle port heads, the bolt pattern is different, demanding a unique intake for engines with LS7 heads.

With engine builders making so much power from even small displacement LS engines, the demand for an affordable cast aluminum intake (as opposed to a custom-built sheetmetal aluminum intake) was great enough to warrant a wide selection of manifolds. We’ve split this approach into carbureted and EFI categories so let’s get started.

If you’re considering giving a more nostalgic look to your LS, consider the dual four-barrel manifold (PN 300-120 for cathedral port heads) that can mount a pair of small Holley four-barrel carbs to give it a mid-‘60s vibe.

Carbureted Intakes

For those true believers whose world revolves strictly around carburetors, Holley has you covered with an immense array of different manifolds basically split into dual and single plane versions.

The dual plane intakes are intended for milder street applications where the focus is on broad street power and torque at lower and mid-range engine speeds. A combination like a cathedral port 6.0L with a mild hydraulic roller cam would benefit from a Holley dual plane intake and a 750 cfm Holley carburetor. We’ve listed some of the applicable manifold part numbers in the accompanying Parts List. Of course, there are also dual plane intakes for the rectangle port heads like the LS3/L92 engines so those engine owners don’t have to feel left out.

There’s also a certain faction of car builders who really like multiple carburetors on top of an LS engine and Holley is able to feed that need with a carbureted dual four-barrel intake for both the cathedral port and rectangle port engines. These manifolds are one of a few that cross over into the EFI side with different part numbers machined to accept multi-point fuel injectors. We’ll get to those in a moment.

Because the cylinder heads in the LS family of engines move such a fantastic amount of air making big horsepower, the single plane family of carbureted intakes has a huge following. The key to making power with carbureted intakes has a lot to do with the height of the carburetor mounting pad. The greater the carb height over the plenum floor, the more potential it has to make better horsepower. This has much to do with creating a gentler radius for the fuel to make the transition into the ports in the head. To this end there are several options for single plane carbureted intakes.

The shorter single planes offer sufficient clearance to clear increasingly lower hood lines and for many cars, this is a benefit. These shorter single planes are available for both cathedral and rectangle port heads for the standard 4150 style carb mounting flange.

It wasn’t all that long ago that a max-effort LS single four-barrel race engine demanded a fabricated sheetmetal intake. Holley proposes to make life easier with a line of race-inspired intakes for both cathedral and rec port engines featuring a vertical split directly through the center of the intake. This allows easy access for custom porting. This particular intake (300-256) sports a 4150 mounting flange for cathedral port heads but there’s a similar 4500 (300-295) mount version also available.

But with ever-escalating LS horsepower levels, Holley raised the ante with a series of tall, race-inspired single planes that are split vertically down the center. These manifolds come in both square 4150 and Dominator 4500 carb mounting patterns. This is another manifold that carries over into the EFI portion of this discussion with similar castings except they are fitted with multi-point EFI injector mounting locations.

There’s also a Mid-Rise 2x4 manifold for both the cathedral port and rectangle port LS Gen III/IV engines. This is essentially a dual plane intake manifold intended for a pair of 4160 Holley carburetors mounted inline in the traditional old school manner. The 4160 carbs are shorter in overall length and therefore will mount in the traditional fore-aft position that also makes the throttle linkage much simpler. Smaller engines like a 5.3L or 5.7L would probably work best with 390 cfm carburetors while larger engines like a 6.0L or stroker might respond to a pair of 600 cfm carbs and up.

Raising the roof for high-rpm manifolds takes us to a Holley Hi-Ram manifold fitted with a dual four barrel lid to mount a pair of Holley carbs. This cast aluminum Hi-Ram base is currently offered for all the different LS family members including the LS1/LS6, LS3/L92, LS7, as well as the LT1 GEN V and is available with a five different tops. For those hi-rpm, peak horsepower guys, there’s a lid to accommodate a pair of 4500 Dominator carburetors or you can downsize slightly to a pair of 4150’s. If you want to be different, there’s even a blank lid where you can create your own induction orientation.

EFI Intakes

Here is the Mid-Rise manifold installed on Holley’s C-10 Chevy pickup, giving it a decidedly aggressive under-hood appearance.

It’s probably best to start the EFI section with a quick nod to all the single plane EFI intakes that are essentially duplicates of their carbureted versions except that these intakes are blessed with the requisite fuel injector bungs. This allows the simple conversion to fuel injection while minimizing converting a dozen other small details.

To aid in this somewhat simple conversion, Holley offers a standard 4150 carb-flange throttle body that will bolt right in place of a carburetor with minimal drama while fuel is supplied by the eight injectors with one injector per cylinder. Holley also makes a dedicated fuel rail for these manifolds so you don’t need to adapt anything.

The limitation, if you want to call it that, is that these single plane manifolds utilize very short intake runners. This limitation has the direct effect of pushing peak torque upward in the rpm band and making the engine a bit peaky. This is fine for those searching for ultimate peak horsepower, but for street-driven engines, it’s advisable to emphasize power in the midrange by increasing the runner length.

Toward this goal, Holley has created three, cast-aluminum EFI manifolds in different heights. These include the Low-Ram, the Mid-Rise, and the Hi-Ram intakes with monikers that are self-descriptive. Manifold selection can be a bit convoluted so we’ll attempt to simplify this while promising to not salt your eyes with arcane math formulas.

But there’s much more to choosing an intake manifold that just simplifying the Three Bears fable and choosing Momma over Papa or Baby Bear. The variables that muddy the water when selecting an intake manifold involve items like plenum volume, intake manifold runner size (cross-sectional area), runner length, and the tuning effect of runner taper. Entire engineering books have been written on this subject, but we’ll try to condense this down to a quick lesson in how these variables all contribute to making power.

In this great country, it seems there is a predisposition toward the Texas Effect which simply states that if some is good then more is better. The Big Texan steak palace in Amarillo, Texas offers a 72-ounce steak dinner for free to anyone who can eat the entire dinner. We’re of the opinion that these over-achievers who have accomplished this feat clearly are from a different planet. When it comes to performance intake manifolds, bigger is often considered the best. But given the demands of internal combustion, sewer pipe intake ports for a 5.3L LS street engine are not desirable unless your engine intends to spin upwards of 8,000 rpm only on the quarter-mile or perhaps on the receiving end of a blower or turbocharger.

The Hi-Ram offers the most aggressive appearance of all the cast Holley manifolds but with the long runner lengths also offers the strongest mid-range potential for a normally aspirated LS engine. These manifolds can be purchased individually or with matching fuel rails and mounting hardware. This particular manifold is configured in the optional black matte finish that is available on many Holley intakes.

But if bigger is better, we’ll start by looking at the Hi-Ram. This intake is available for both the cathedral and rectangle port engines and features the longest runners along with a spacious plenum. The plenum is defined as the common area between the throttle and the entries to the intake ports. Large plenums are often useful when combined with supercharged or turbo applications where high air inlet speeds from the supercharger have a chance to slow down and be more evenly distributed to each individual intake port. Even with its height, the Hi-Ram can be used in normally aspirated applications that will benefit from the longer runner length which tends to build more power at more conservative engine speeds while maintaining power into the top end.

An example of the effect of runner length can be understood by comparing the runner lengths of a stock LS truck manifold to the shorter length passenger car manifolds. The truck manifolds are typically taller and larger to accommodate the longer runner lengths. As runner length increases, this tends to improve low- and mid-range torque, which is what trucks are generally intended to serve. To abbreviate what would be a long, boring dissertation on intake runner tuning lengths, the facts boil down to a simple statement that as runner length increases, low- to mid-range power increases at the cost of top-end power. The opposite is also true that as runner length is shortened, peak power improves at the cost of low- and mid-range torque.

Oddly, while the Hi-Ram may appear to be a high-rpm race manifold (which it can still clearly serve), it offers the best improvements to mid-range power for larger displacement, normally-aspirated LS street engines. Elsewhere in this story, we’ve included a photo of car builder Scott Sullivan’s LS3-based, 427 stroker, LS-powered ’54 Chevy equipped with a custom-painted Holley Hi-Ram intake. Sullivan reports that even with this overly-large intake that engine part-throttle response even at low rpm is impressive.

While some may think that Holley shaped the lid on the Hi-Ram to give it a menacing, praying mantis-like appearance, the actual reason, according to Holley engineer Coy Hudnall is that “with single bore throttle valves, the inertia of the air entering the plenum tends to pack the cylinders farthest from the inlet. Our CFD simulations and dyno testing showed that our plenum shape helped to even the distribution.” His CFD reference is to a computer program called Computational Fluid Dynamics. This program simulates the movement of a fluid (in this case air) inside a manifold. Based on this information, there’s a tremendous amount of engineering that goes into these manifolds that extends way beyond simply connecting the dots.

As with the carbureted lid for the Hi-Ram, Holley offers both a 95mm and a 105mm front-facing throttle body flange tops for this intake along with the requisite blank top for those willing to fabricate their own. There’s even a lid ring that offers the opportunity for the adventuresome to create a sheetmetal top for their own unique Hi-Ram creation. The only limitation is your sense of adventure.

The next step in terms of height is the Holley Mid-Rise. The manifold uses a 2x4 style base manifold with an intermediate plate sandwiched in between the base and the lid. The intermediate plate adds a slight amount of runner length to the Mid-Rise manifold that taper into the 2x4 entries in the base. This 2x4 Mid-Rise is offered in both cathedral port and rectangle port versions. The lid selection for the Mid-Rise enjoys the same optional lids as the Hi-Ram manifold. For example, lids can be ordered to accommodate either a 92mm or 105mm forward facing throttle body.

The Lo-Ram is aimed at vehicles with tight hood clearance but is also a perfect candidate for supercharged or turbocharged power-adders. It is available with dual fuel injectors per cylinder, a front-feed inlet, a top-feed inlet, and an SFI burst panel. Because LS induction systems are symmetrical, it’s also possible to mount the throttle body pointed toward the rear of the engine if the application demands it.

On the opposite end of runner length spectrum is the Low Ram. This EFI version upgrades the carb version with mounting bungs for individual fuel injectors and goes further by offering several lid configurations depending upon your choice of throttle bodies. The simplest is a front-facing tapered lid with a provision for a single blade, four-bolt throttle body. This is the shortest of the front throttle body EFI manifolds and is designed to be used in applications with a low hood line, such a 4th gen Camaros and C5 Corvettes, or for other manifold height limitation applications. The Low-Ram is only available for the LS1/LS2/LS6 and other cathedral port intake manifolds and not for the rectangle port engines.

Among the different options for the Low-Ram is a lid for power-adder applications that incorporates a burst panel which is designed to vent manifold over-pressure caused by an engine backfire. The panel measures 6.125 x 3.125 inches and is retained with a series of 25 10-32 machine screws. The actual burst panel and hardware are available through outside aftermarket vendors such as All-Star Performance, The Blower Shop, and Specialty Fasteners. Holley does offer a vertical aluminum burst panel duct that directs the over-pressure away from vehicle bodywork (PN 300-608).

Another option for the Low-Ram base manifold is one fitted with two injector bungs per intake port for applications demanding maximum fuel flow in E85, Methanol, or race gas applications, or perhaps a staged set of injectors. The manifold can be purchased bare or with Holley fuel rails to make the installation a bit simpler.

So far we haven’t touched on the LS7 or the Gen V LT1 so let’s hit them here. The LS7 is not limited to a selection of the Hi-Ram manifold but also includes a carbureted style EFI single plane intake either with or without fuel rails. The LT1 is similarly outfitted for Hi-Ram applications but offers an interesting twist. While the LT1 is a direct-injected engine with high-pressure ports aimed directly into the combustion chamber, you can add an Hi-Ram manifold that retains the stock direct injection but features untapped bungs that can be used for nitrous or water/methanol injection.

Leading-edge performance engine builders are also experimenting with the advantages of adding port injection to the LT1 for supplemental fueling capabilities. Holley has addressed this demand with the option of adding a Hi-Ram with port fuel injector bungs along with a dedicated fuel rail. Of additional note is that one problem with direct injection is a tendency for street-driven engines to experience carbon buildup on the back side of the intake valve because there is no fuel there to clean deposits. One minor advantage to adding port injection would be to keep the back side of the intake valves clean.

As mentioned at the beginning of this story, this piece has concentrated on just the cast aluminum pieces from Holley. We’d need a completely different story of equal length to outline the Sniper lineup of sheetmetal intakes, not to mention the slick composite piece from MSD as well as other lists of intakes from companies within the Holley family. The LS engine family has introduced an entire galaxy of opportunities for the LS engine builder. All you have to do now is narrow the selection process down to perhaps four or five really good choices for your next LS build. It’s a good problem to have.

Note: All dimensions are in inches. Height is measured from the tallest point of the manifold to the cylinder block lifter valley flange. Length is overall front to rear. These are Holley measurements while the TrailBlazer SS intake height was taken from an engine with the manifold installed.

Note: The runner length dimension is only for the Hi-Ram manifold. The Mid-Length and Low Rise manifolds will obviously be shorter. Taper refers to the gradual reduction in area from the plenum entry to the manifold exit.