Designing intake manifolds is a balancing act, where the goal of maximizing performance, efficiency and reliability bumps up against practical limitations. That means optimizing the air-fuel mixture often requires trade-offs, as it’s rarely possible for engine builders to check every box.
“For starters, it still needs to fit underneath the hood,” says David Visner of Visner Engine Development (VED) in Grand Rapids, MI. “You can’t always get the perfect runner length and the perfect amount of taper and all the calculated numbers you want, so you have to compromise and make it fit, and choose what’s most important for that application based on experience.”
To drive home the point, Visner highlights the difference in approach to designing manifolds for naturally aspirated (NA) vs. boosted engines. In NA applications, he says, the focus is on optimizing runner length to maximize the tuning pulse effect and extract every bit of power possible. However, boosted engines offer more flexibility, where “you can crunch it and make the runners a little bit shorter and the plenum a little bit bigger” to slow the airspeed and stabilize airflow within the plenum.
With boosted engines becoming increasingly common, where shorter runners allow well-tuned intakes to fit in tighter spaces, Caleb Newman of Auburn Hills, MI-based Performance Design, has adapted his product line to meet these evolving needs.
“Our Carbon TRc runner is one-third the length of the Carbon XR in some applications,” he explains. “The Carbon TRc came about from considering the prevalence of boosted engines today, and we drew from our older Carbon TR manifold styling, combining it with shorter runners and a lower profile to fit under hoods.”
Consider the scenarios Visner faces with small-tire cars. Here, the high-speed airflow entering the plenum from the front creates a Helmholtz effect, similar to blowing across the top of a bottle, he notes, which lowers pressure at the front cylinder entries.
“To counter this, we tend to oversize the plenums, because it pressurizes the plenum more evenly and helps with air distribution between the cylinders,” Visner says. However, when you factor in the rpm range many of these engines run in, it can compromise tuned runner lengths, so there’s a trade-off.
Ultimately, Visner says, it boils down to tailoring the manifold to an engine’s intended use. “The fundamentals haven’t really changed…we just keep refining them.”
For VED and other leading manufacturers, advanced techniques and innovations are helping them refine processes all the time, allowing for greater customization while improving engine performance and reliability across a wide range of racing and street applications. Let’s take a closer look at some of the key developments pushing intake manifold design to new levels.
3D Printing
The emergence of 3D printing has undoubtedly transformed manifold development, enabling faster prototyping, testing and production of custom components. Manufacturers like Performance Design use this technology to experiment with runner lengths, cast custom seals and even fabricate production parts “because the materials are robust and have much higher specs for temperature and strength that can run on an engine long term,” Newman says.
In addition to speeding up the development cycle, 3D printing also allows engine builders to tailor manifolds to specific performance needs, “like tuning runner lengths to optimize a manifold for a specific engine operating range,” Newman adds. In other words, builders can now fine-tune designs without expensive tooling, letting them make complex adjustments in a fraction of the time.
At Trick Flow Specialties in Tallmadge, OH, engineers use 3D printing to prove out the real-world performance of their intake designs earlier in the development process. “CAD design and simulation are good starting points,” Josh Cook says, “but the proof is on the dyno, and the sooner we can validate performance characteristics of a new design, the better. Dyno testing a 3D-printed part allows us to do this before we invest in casting tooling, after which design changes become significantly more costly and time-consuming.”
The testing process presents some unique challenges, including sealing porous material against vacuum, managing unequal thermal expansion rates, and addressing NVH. As Cook notes, “It takes a few tricks to get a 3D printed part up to the task of surviving on a running engine. And, you have limited time before heat, fuel and vibration begin to take their toll.” This is why capturing real dyno data earlier has been invaluable to Trick Flow’s product development.
One of the most significant advancements in 3D printing is its application in manufacturing cast manifolds, especially in high-performance racing. In recent years, more classes have restricted the use of billet parts, prompting competitors to explore 3D-printed sand castings, Visner notes.
“Rather than doing your traditional tooling to make a core box, with the sand core in it, which would require tooling,” he explains, “they print the sand directly in the sandbox, and then they can pour one at a time. For prototypes, we can basically make any of our billet manifolds one piece in a cast version. Honestly, I think it’s going to start backfiring on some of these regulatory bodies [that are] trying to keep the cost down by mandating cast manifolds, because now people can just simply get anything made in a cast version.”
CFD & Wet Flow Testing
Computational Fluid Dynamics (CFD) has become another indispensable tool in modern intake manifold design. Newman and his team at Performance Design utilize dynamic CFD analysis to optimize airflow, incorporating the engine’s firing order and valve events rather than static boundary conditions like those measured on a flow bench.
“Periodically, we’ll be asked what our manifolds flow on a flow bench,” he says. “This isn’t a number we’re overly concerned with, because unless you really mess something up, the intake manifold is rarely the limit in ultimate airflow. We look at total mass flow in dynamic CFD to ensure that we’re flowing through the entire engine cycle more than the competitive benchmark or our iterative designs.”
In addition to dynamic CFD, Newman uses a proprietary technique called “acoustic tuning.” This method analyzes the 3D-tuned length of each runner, accounting for interactions with the plenum and surrounding geometry. While a runner’s centerline length might measure as X, the actual tuning behavior – affected by the plenum and other design features – might make it act like length Y, which could be less than ideal for the desired operating range. Unlike simple 1D wave tuning, this approach fully considers the manifold’s complex 3D design.
“We couple the effective tuned length analysis with dynamic CFD results to tailor the runner lengths, make adjustments to plenum shape and volume, and even evaluate the construction of the manifold,” Newman explains. “With all this, we are trying to develop a manifold that will work for the maximum number of users.
“Of course, intake manifolds are part of a system,” he adds, “and the interaction with cam, heads, and exhaust can make one design better or worse for a specific engine. In these cases, we often have different runner lengths, so an engine builder can tailor the tuned length for his application.”
For 1 Way Technologies in Washington, IN, CFD has helped speed up product development, but wet flow testing remains a cornerstone of their approach, leveraging decades of design experience to refine port designs and achieve uniform cylinder distribution.
“We’ve made significant gains there, where we don’t have one cylinder being much richer or leaner than the other,” Jeff Jones says. “I think we’ve probably gained more in that area than we have in others.”
These advancements have allowed Jones to explore and implement design strategies that previously seemed unfeasible. One example is the progress they’ve made with runner length and shape modifications. By leveraging pressure wave dynamics, he says, the team can now enhance cylinder charging in ways they couldn’t only a few years ago.
One of the main hurdles was cylinder head design, which played a major role in determining what could be accomplished with the manifold. “When we tried to do some of the things we thought would take us in the right direction, it never proved out on the racetrack, whether it was drivability, or maybe the curve wasn’t where we wanted it to be,” Jones says.
Advances in cylinder head development have opened up new opportunities, enabling 1 Way Technologies to do things it wanted, but were never able to prove out – now they can. “A lot of it really does go hand-in-hand with cylinder heads – as development increases, and you’re able to make that a better, viable part, then it absolutely does change what you can do,” Jones notes.
Materials
Material innovation has become a cornerstone at Performance Design, where nylon and carbon are the team’s top choice due to their benefits in weight savings, strength and thermal insulation vs. metal.
“Carbon is stronger than steel and lighter than aluminum,” Newman says, “and has a low heat transfer coefficient, so it keeps the air charge cooler. Less mass helps vehicle dynamics, and a cooler air charge makes more power.
“Nylon is also great for intake manifolds due to its low weight and good insulating properties. Nearly all production OE intake manifolds are nylon reinforced with milled glass, PA6 G30. We use nylon in our intake manifolds to help reduce the ultimate production unit price.”
Despite the significant upfront investment required for injection molding tooling, Newman tells us it does allow for more competitive production costs over time. That said, in order to maximize strength and weight, and account for production volumes, Performance Design will often combine materials for different components like runners, plenums and flanges. All materials have pros and cons and a fit for some areas of the intake.
Newman cited their XS manifold as an example, where the team invested in injection molding tooling to produce a competitively priced underhood LS3 intake that delivers both power and torque. He also pointed to a proprietary in-house nylon casting process called NylonMold, which allows the team to create polymer parts with significantly lower upfront tooling costs.
“In our Carbon pTR manifold line, we use NylonMold runner banks and lower plenum, injection molded runners and bellmouths, and carbon upper shells to blend the strengths of each material where it best suits strength and function and balances cost,” he says.
Future Innovation
Looking ahead to opportunities for further innovation, Visner highlighted fuel placement within the manifold. “We’re doing a lot with different fuel injector locations and different numbers of injectors and how the injectors behave,” Visner says.
Positioning the fuel higher in the intake runner is generally better for maximizing peak power, Visner notes, as it allows more time for atomization and helps cool the intake charge, whereas for part-throttle response, placing the fuel closer to the valve tends to deliver better results. In modern emissions-focused applications, fuel is often introduced directly into the combustion chamber. Each approach clearly has its own application-specific benefits.
“We have a pretty good idea of what we’re trying to do, but these fuel systems are so [much more] capable of running multiple injectors now, where that wasn’t really the case even 10 years ago,” Visner notes.
Another trend that’s become increasingly popular of late is integrating intercoolers into manifolds, particularly in high-ram designs for street cars, Visner tells us. A common challenge remains, however: limited space under the hood.
“When air is compressed by a turbocharger or supercharger, it heats it up,” he says. “The air on a 90-degree F day can reach over 400 degrees F in the plenum after going past the throttle body. Cooling that air charge with an intercooler is always better. It cleans up the tune up and makes more power. It’s just a win-win by cooling that air.”
This approach has especially caught on among streetcar enthusiasts running gasoline. “Our [engines] are on methanol, or boosted applications, so we don’t have a huge problem with that because the alcohol has a cooling effect,” Visner adds. “And the weight it adds for race cars isn’t always a good trade-off. But on streetcars, it’s really common right now.”
As with any engine component these days, manufacturers are utilizing every technology they can to find performance gains. EB
