Go with the Flow
What makes the GT350 intake so good and how it can be better
By Steve Turner
Photos by Steve Turner and courtesy of Ford Performance
Over the last couple of months we have seen some interesting test results involving the Shelby GT350’s intake manifold. Not only did this intake hang in there versus the racy Cobra Jet intake on its native engine—the Voodoo 5.2-liter—but it also handily outperformed the stock manifold on a 2015 Mustang GT. As a result, we wanted get some insight into what makes this intake perform so well.
To learn how Ford Performance engineers developed this well-rounded intake manifold, we spoke with Eric Ladner, the 5.2-liter Voodoo Engine Program Supervisor at Ford Motor Company.
“This whole engine, because the 5.2 was designed specifically for the GT350, it’s really the only product it designed specifically for. A lot of times we have an engine off the shelf and we might try to tweak it for the vehicle’s needs. Of course when the 5.0-liter goes in a truck versus a Mustang it gets a completely different intake for a different function. So you can modify an engine in that way,” Eric explained. “However, this overall engine was going to be an engine for the track. Of course, we wanted a lot of performance out of it, so that’s a given. But, we wanted more than just a high horsepower number or a high torque number.”
These days much of the engineering and development is performed using computer-aided engineering tools. In fact, the simulations are so good that the parts are pretty much ready to run by the time the hardware is produced in the real world.
“Using CAE for complete design of this engine allowed us to deliver this engine in time. The first prototype engine that we produced made of 500 horsepower within one week of getting it on the dyno,” Ford V8 Intake Combustion and Exhaust Technical Specialist Adam Christian said during the media presentation for this engine back in June of last year.
When it came to the Shelby GT350’s intended purpose, the engineers had a specific yet broad target for this Voodoo engine, and a big part of achieving that performance is the design of the intake manifold.
“When you look at our vehicle track simulations and the data from the track, it operates in the 4,000- to 8,250-rpm range. It lives there all day. It never really drops below that, so we wanted to make sure we were delivering a high and flat torque curve throughout that whole range,” Eric said. “We could put really short, fat runners on it and get a bigger—potentially—peak power number than we did, but we would sacrifice some low-end torque; Same thing on the other end. We really wanted that balance to make it flat through the entire range and as high as we could, and the intake manifold, combined with the flat-plane crank, is a huge part of how that’s delivered.”
Yes, the old days of hot rodding where bigger is always better, are long gone. Ford engineers combine a one-dimensional tool that simulates the performance of an engine with the three-dimensional tool that simulates the geometry of its parts to gain insight into how the engine should perform.
“Once we get into the details of the intake manifold, we use a 1D/3D co-simulation. There are 3D CFD tools that resolve the fine details of the geometry of the intake. You use the 1D code to does the engine performance and they pass boundary information back and forth to each other at the inlet and outlet,” Eric explained. “So now we are resolving the three-dimensional geometry of the intake and we are seeing if what we are executing is delivering what the 1D tool thought we would and then we optimize from there.”
This is an ongoing process that allows engineers to experiment with the design. In this case, Eric could even compare the evolving GT350 intake with its predecessors, like the Boss 302, and keep tweaking the design till it delivers the targeted performance.
“Not only that we can then look at the results to find out where to tweak and make it better. Where are the losses happening? Where can we improve?” Eric said. “It’s not just ‘here’s the number,’ you can look back at the 3D results and find out that there’s flow separation happening here or this cylinder’s weak or we’re getting great volumetic efficiency, but we are getting poor trapping in the cylinder. Those types of things really help us with the development.”
As you might expect, the Eric and the rest of the Voodoo team were laser focused on maximizing the performance of this intake for the 5.2-liter engine, so they didn’t consider how it might perform on other engines in the Coyote family.
“It does not surprise me that the manifold performs better across the board than the 5.0-liter manifold. The only thing I wasn’t sure of is that because we have bigger diameter runners and we also have bigger diameter ports (on the 5.2) so when you put that larger-diameter manifold on a 5.0-liter head, you are going to have a bit of a step down to the port size, so I wouldn’t know without having the team do analysis how much of a negative affect that would have,” Eric added. “…Taking that step out of the equation, I’m not surprised at all because it wasn’t like a truck versus a car manifold where we said we want this to tune hard for peak torque because it’s a truck and we want this Mustang GT to tune hard for peak power, therefore you had trade-offs. It wasn’t really a trade-off, it was kind of go after it all because we were trying to raise that whole torque curve up.”
In fact, for a minute, Eric thought the Voodoo engine might need an intake with the plenum on top and straight runners feeding the heads, but he and the engineering team were able to develop an easier-to-package, scroll-style intake that hit the performance sweet spot.
“… I thought we were going to have to push for more hood clearance or some kind of compromise. Everybody looks at those and says, ‘Oh, those (intakes with plenums and straight runners) are better.’ They look better and in the past they have kind of functioned better,” Eric said. “But, somehow with the way we put the design together and implemented it, when we compared it to a similar design with a different configuration we really got it as good as we could have.”
What they achieved is definitely impressive, but ultimately the GT350 intake is limited by the size of its throttle body.
“Both manifolds were designed using the same Ford proprietary software to create the best airflow path for a given package. So they have the same roots and similar high-rpm targets,” Ford Performance Parts engineer, Dave Born explained. “The GT350 manifold was designed for the new vehicle platform which has a much lower hood line and necessitated the scroll style design to stay under the hood with the proper clearances maintained. And, it uses a single-bore throttle body which is much easier to tune for low-rpm operation with fuel economy and emissions in mind.”
That’s why FPP opted to utilize the Cobra Jet intake manifold for its cross-plane 5.2-liter crate engine.
“The Cobra Jet manifold is designed for the larger dual-bore or oval throttle body, which provides more airflow to the manifold than the GT350 throttle body. The Cobra Jet intake runners are straighter and therefore have less flow losses,” Dave added. “While the GT350 manifold is a great part, the CJ manifold will give a bit more power—and we were looking for the highest output we could get on our top-of-the-line Coyote based crate engine.”
While the CJ is the ultimate choice at the moment, Ford Performance engineers are developing two throttle body options to push the performance of the GT350 intake to a higher level.
“We are looking at a few different throttle bodies,” Jesse Kershaw, Drag Racing Parts and Competition Manager at Ford Performance, told us. “One 92mm unit that looks very OE but requires an adapter for either the GT350 or the GT manifolds. This will be a value entry with a target jobber price of around $250-$300 including the adapter. Then we’re working on a 100mm unit that would be billet polished in the $600-$700 price range for the GT350 manifold.”
So Ford Performance Parts has two great intake options for the Coyote engine family. As we have seen, the GT350 is definitely a player, especially for those that want more performance without the need for extra hood clearance. We’ll have more intake testing in the future, but now you know why this manifold performs so well and how it might perform even better in the future.
While it was original equipment on the Shelby GT350, this manifold (PN M-9424-M52; $1,495) is available on its own via Ford Performance Parts. It is a highly effective bolt-on upgrade for Coyote-series engines, especially those installed in cars where hood clearance is a concern.
Likewise, you can purchase the companion GT350 throttle body (PN M-9926-M52; $249) from FPP, but you will need a custom calibration to make this setup run properly on your Coyote-powered Mustang. This throttle body features a progressive bore that starts at 87mm and tapers down to around 85mm. It offers better low-rpm driveability while flowing just as well as a straight 90mm throttle body. Ford Performance Parts will eventually offer even larger throttle bodies to maximize the performance of the GT350 intake.
Ford engineers use a variety of computer-aided engineering tools to develop an intake manifold for its intended engine application. For something like the Mustang GT (left), it is optimized for peak power without giving up too much down low, while the GT350 intake is designed for broad powerband from 4,000 on up.
One aspect of the GT350 intake manifold that received a lot of attention and tweaking from the engineers was the plenum. “…We want a certain volume of the total throttle air mass. Usually more is better, but if you go too high, then you get sluggish response,” Eric explained. “The air has to fill the manifold before it gets to the runners, so if you put a huge plenum on there, it’s kind of great for power, but it’s not as responsive. There was a lot of massaging of the plenum and the transition into the runners to get the performance.”
The GT350 intake was engineered to provide a fat powerband from 4,750 to 7,500 rpm, but it was still able to do so with a scroll design like its Mustang GT cousin, albeit with taller, larger-diameter runners.
