Now that GM’s Gen V small-blocks have been on the market for more than half a decade, enthusiasts and racers are starting to wrench on them in rapidly-increasing numbers. And whether an engine is pulling daily driver duty or living at the track, the intake manifold is one of the first components that builders turn to when seeking ways to coax out some additional power. But as has been the case since the dawn of hot rodding, a solution for one application isn’t necessarily the most ideal option for another.
Here we’ll look at two intake manifolds offered for the modern LT1, the MSD Atomic AirForce LT1 and the Holley Hi-Ram LT1. Both manifolds were developed to deliver performance gains over the factory manifold while also taking into account the unique characteristics of the LT platform, but the two designs are ultimately geared toward the goals of fairly different applications. Here we’ll take a closer look at how those goals affect the overall design, and where each of these manifolds will really shine.
MSD GOES ATOMIC WITH THE LT1
“We introduced this manifold at the 2015 PRI show,” explains MSD’s Jamie Wagner. “So it was introduced fairly early on after the introduction of the LT1 itself. It was essentially a logical extension of the current lineup, continuing to develop parts for this new engine as MSD had done with the LS platform before it.”
Considering the brief amount of time that the LT1 had been out in the wild at that point, very few examples of this new power plant had already been earmarked for hardcore race duty. Instead, where the LT1 was making its presence known at the time was under the hood of the equally-new C7 Corvette, and a few years later, in the engine bay of the sixth generation Camaro SS as well as GM’s latest full-size trucks and SUVs in a slightly altered form.
Since all of these vehicles spent the vast majority of their time on the street, MSD saw fit to tailor their approach to the manifold’s development to that expected application – with some room to grow later on, of course.
MSD’s manifold has built-in provisions to add a secondary port injection system for builders who’re reaching the limits of the factory direct injection system.
“It’s intended for the street more than anything, and the design reflects that,” Wagner says. “But we did make sure builders would have the ability to easily add secondary injectors if someone needed to get more fuel into the engine than the direct injection system was capable of providing on its own.”
MSD knew this street-focused manifold faced some constraints early on: It needed to fit in more or less the same amount of space afforded to the factory manifold and provide power gains in the same engine speed ranges where the stock piece does its best work. So to make sure they would be delivering a compelling piece in variety of applications, MSD set out a few priorities early on in the development process.
“Of course the primary focus was to make sure there was a tangible, real-world performance gain to be had,” Wagner tells us. “And MSD didn’t want to create another also-ran aluminum piece, so some significant effort went into finding the right supplier to produce this type of casting in this type of special composite material.”
MSD’s design adds a bit of visual flare to the engine bay, too.
Right out of the box, some of the MSD Atomic AirForce intake manifold’s benefits over the stock piece are immediately obvious. “The stock manifold isn’t much to look at when you take the engine cover off of an LT1,” Wagner points out. “And something MSD wanted to provide was a part that would be eye-catching when you pop the hood, while also making more power.”
In terms of the former, the MSD manifold adopts much of the aesthetic of previous entries in the Atomic line. “It’s really an approach where you take a stock manifold and think about ways to make it look better than it does without compromising the performance,” he adds. The result is a contemporary approach that fits with modern muscle cars – smoothed out with no external ribs.
While producing this part in aluminum would have been easier and cheaper rather than opting to use a purpose-built polymer material, Wagner notes that the benefits it offers made it worth the effort.
The manifold also features a 103mm throttle bore, so it’ll play nice with a larger aftermarket throttle body, and its two-piece design allows for easy access to the runners for porting.
“The weight savings is the first thing – you’ve got a pretty good-sized part on top of the engine there, so anything we can do to minimize that is going to be beneficial. But one of the other big things was simply whether it could be produced the way we designed it. It would be very difficult to manufacture this manifold in aluminum because of the shapes involved and the thicknesses that you need. You can do things with this polymer that just can’t do with aluminum without it costing a fortune. The material also allows you to do things with heat rejection that you can’t do with aluminum either, so there are a number of reasons why it made sense to go this route.”
HOLLEY TAKES THE HI ROAD
The LT Hi-Ram is one of the latest performance parts that’s been developed through a collaboration between Holley and General Motors on Chevrolet’s factory-built drag car.
When developing the Hi-Ram intake manifold for the LT1, Holley had some different considerations to take into account than the folks at MSD did with the Atomic AirForce, and those factors in turn resulted in a decidedly more motorsport-focused approach.
“It was developed in conjunction with the direct injection controller that we were working on for the COPO Camaro program,” recalls Holley Performance engineering team manager, Adam Layman. “GM came to us in 2015, and up until that time, all of the modern COPO Camaros had been LS based. They were looking at adding a powertrain option that was a 6.2-liter naturally aspirated LT engine. They brought us an engine, which we had on the dyno for quite a while doing development on the high pressure fuel controller, and we did the intake manifold at the same time.”
Holley looked to its previous development work on the Hi-Ram manifold for the LS platform as a foundation for this new piece, some of which came out of necessity. “GM had a few design constraints they wanted us to follow,” Layman says. “They wanted to it to be approximately the same height as the LS Hi-Ram, and we worked with them on what they wanted for intake runner taper and length – things like that.”
As with previous entries in the Hi-Ram lineup, the manifold’s tunnel ram-style design provides the biggest benefits for high-revving, highly modified LT power plants.
Fortunately both GM and Holley were on the same page when it came to design philosophy. “Their guidelines aligned well with what we wanted to do for something that would be good for public consumption,” he adds.
And part of that involved modularity within Holley’s own Hi-Ram ecosystem. “So we designed it to be compatible with the existing Hi-Ram tops that we already had for the LS Hi-Ram.”
But Layman notes that the manifold’s overall design is far from being a carry-over from the LS Hi-Ram. “The LT is a very different beast. The intake port on the LT is really, really good, so it was kind of nice to have that to use as a starting point. But one of the big differences with this motor is that, with the direct injection, the manifold is dry – there is no fuel going through the intake manifold like you have on an LS with port injectors. When you have air and fuel occupying the same space, it changes the volume you have to work with. So it’s a different animal in how you approach the design, sizing-wise. Also, with the LS you’re relying on the intake and the intake runner to work in conjunction with the combustion chamber and everything else to atomize the fuel, create a good mixture, and all of that. With a LT’s direct injection, you’re kind of doing it with brute force – you’re atomizing the high pressure fuel into the cylinder within a certain range of piston position.”
The LT Hi-Ram is designed to work with all of the LS Hi-Ram tops.
And those differences contributed to the need for a significant amount of testing. Fortunately for Holley, they had some particularly useful hardware on hand. “We were lucky enough to have the COPO engine there to play around with,” Layman tells us. “This was around the time that 3D printing was starting to become more accessible, so this was one of the first intake manifolds where we did 3D printed prototypes and then ran those on an engine. That was kind of exciting, and it was nice to be able to do that because we were able to try a number of different ideas in a relatively short amount of time.”
Like the MSD intake, Holley’s design provides provisions for builders who want to add a supplemental port injection system, but their goals in terms of where this intake really makes its presence known are much more centered on track use in highly modified power plants. “We wanted to be able to extend the powerband well past the factory limit – we knew that anyone who was going to put an aftermarket cam in one of these engines was going want to make power at 7000 RPM and beyond. And we also wanted to provide something that would be strong under boost, something where you wouldn’t have to worry about sealing issues at the flange and that sort of thing."
Beefed-up wall thickness in specific areas of the manifold provides more material to work with when CNC porting.
Holley also took the opportunity to address some of the feedback they’d received from engine builders with the LS Hi-Ram, too. “This time around we added some wall thickness in certain areas around the plenum, where the runner meets the plenum, and down towards where the flange meets the head,” Layman says. “It was kind of one of those wish list things from the LS Hi-Ram from folks who’re porting the manifold, so we incorporated that into the LT Hi-Ram.”
As a race-ready piece, Holley knew the manifold would need to really perform at the top end more than anywhere else in the powerband. “The benefits are from 3000 RPM on up,” Layman says. “But with the COPO engine, we ran those to about 8400 RPM, just a little past peak power on those engines. The manifold itself is an 8500 RPM-capable piece for sure.”
At the end of the day, while both the Holley Hi-Ram and MSD Atomic AirForce LT1 manifolds are designed to deliver improved performance over their factory counterpart, each had a specific application in mind which dictated their designs from the get-go. Will the Hi-Ram work on a street car? Certainly (though you may have to cut a hole in your hood). Will the Atomic AirForce work on a race car? Absolutely. But each has been built to do its best work in its intended use-case.
And that, friends, is why variety is a wonderful thing.