How the Cobra Jet intake compares with the factory intake on a GT350
By Steve Turner
We recently found out that the intake manifold atop the GT350’s Voodoo 5.2-liter engine is a great upgrade for the Coyote 5.0-liter in the Mustang GT. The intake seems to gain horsepower on the smaller engine without giving up any torque. That got our wheels spinning. How might Ford Performance Parts’ racy Cobra Jet intake perform atop the rev-happy Shelby’s engine? Fortunately VMP Performance owns a new GT350 and has the wherewithal to facilitate such a test.
VMP Performance’s Justin Starkey spent a lot of time on the dyno and racetrack learning what kind of calibration tweaks can maximize the performance and driveability of the company’s new Shelby GT350 project car.
We asked VMP’s Justin Starkey if he were willing to test the Cobra Jet intake on his new GT350, and he didn’t hesitate for a second. He ordered the intake and scheduled the dyno time. Once we arrived camera in hand, Justin was ready for even more science. He suggested that we also try a Mustang GT intake manifold as well.
“We’re still learning about the Voodoo,†Justin said. “Testing the different intakes helps us figure out where the power comes from. We know the cylinder head is better, the flat-plane crank is better, and the intake is apparently really fricking good.â€
The most highly tuned naturally aspirated engines Ford Performance has produced to date made for an ideal test bed for intake manifolds. While the results might not translate directly to how these intakes will perform on a 5.0-liter, they do show the maximum potential of each design.
You can see the test runs in action right here…
When we asked if Justin if he was willing to test the Ford Performance Parts Cobra Jet intake (right) on his new GT350 (center), he didn’t bat an eye. No sooner did we ask and he had an intake on order. Once we arrived for the testing, he suggested that we also test a Mustang GT (left) intake manifold to see how it compared as well.
“The GT intake showed us that even a Ti-VCT engine is not immune to low-end torque gain or loss from intake-runner design,†Justin added. “The Cobra Jet intake showed us that the stock GT350 intake is really good. There is a tiny bit of area under the curve on the CJ, but I don’t think I would ever run one on this car. It would be interesting to test the CJ versus GT350 on a conventional-crank 5.0-liter or 5.2-liter with the GT350 heads.â€
As you would expect the GT intake was superior down low and in the midrange, however the Cobra Jet intake didn’t clearly wipe the floor with the stock GT350 intake. The CJ manifold was a little bit better than the GT350 as the rpm climbed so it might be the move on an all-out race car, but for the street the GT350 intake looks like the one to beat.
In all it was an interesting experiment and we hope to bring you more GT350 intake information in the future, so stay tuned.
Our baseline runs were with all the stock hardware in place and both stock and custom VMP calibrations in the PCM.VMP’s Joe Goodnough and Justin Starkey removed the factory GT350 intake and fuel rails as a single unit.We originally intended to compare a factory 2015 Mustang GT with the Shelby intake, but it turns out that the O-ring seals on the newer GT intake (left) are incompatible with the mounting surface on the GT350 cylinder heads. It wouldn’t seal properly and the resulting vacuum leak wouldn’t let the car run properly.Fortunately VMP had a 2011-2014 Mustang GT intake leftover from a VMP TVS supercharger install. As you can see it has visibly smaller ports than the GT350 intake (right), but the O-ring seal is similar in shape.Joe bolted up the S197 Coyote intake and throttle body before reinstalling the GT350 fuel rail and injectors.Since the GT350 throttle body measures 87mm at its inlet, the GT throttle body is a bit smaller. To facilitate the installation of the Shelby induction tube and airbox Justin used a simple piece of hose to make up the size difference and allow the larger GT350 tube to seal on the GT throttle body.On first glance you might not even notice what’s going on here, but students of the sport know the GT350 manifold is all black. As you might expect this intake picked up some down low and in the midrange, but became a cork as the Voodoo 5.2 climbed to 8,000 rpm.While it was an interesting scientific experiment to try the GT intake on the GT350, what we really wanted to know was how Ford Performance Parts’ racy Cobra Jet intake would impact the high-revving 5.2-liter engine. The intake bolts right on, but there are some quirks with the various connections that would need addressing to make it a pure bolt-on.The Cobra Jet kit includes a new coolant tube for the lower intake, but Joe found that just tweaking the factory tube outboard a bit allows enough clearance for the oval throttle body used on the CJ intake.To feed the CJ intake with plenty of airflow, Joe bolted up one of VMP’s TwinJet 67mm throttle bodies, which have proven to feed enough air to support big-power, TVS-blown Shelby GT500s.Without an S550-specific Cobra Jet intake readily available, VMP employed one of JLT Performance’s CJ CAI systems for 2011-2014 Mustang GTs.Of course the S197 JLT wouldn’t fit under the hood, but for our dyno-only testing, Joe installed it like this. Interestingly it looked like the CJ intake might barely clear the Shelby hood, but with dropped motor mounts it would certainly clear. Naturally you’d need a CAI that works in this chassis to make this system viable for driving.The FPP Cobra Jet intake looks pretty impressive atop the Voodoo 5.2 and it did offer some midrange and top-end gains over the Shelby GT350. Ultimately, however, this test showed just how well the stock GT350 manifold performs.As we said the GT350 baseline included a custom VMP tune. For the GT intake, Justin simply adjusted the calibration to ignore the Charge Motion Control Valves, which are not present on the 2011-2014 Mustang intake. When it came to the Cobra Jet manifold, Justin had to adjust the calibration for the new throttle body, the lack of CMCVs, the volume of the intake, and the cam timing to make the most of its high-rpm personality.It’s interesting to see how the various intakes affected the high-flowing Voodoo engine. In untuned form the 2011-2014 Mustang GT intake picked up some torque down low but proved a major cork at the top of the rpm range. Since the CJ needed some tuning TLC to run properly on the GT350 we compared it with the tune-only GT350 run. The racy Cobra Jet gained and lost at points before 6,000 rpm but it did pull a bit stronger up top. This test showed us the GT350 is a great all-around intake, but the CJ might be the way to go on an all-out race application.Looking at a sampling of the data shows you how much the GT intake helps on a street car. From 3,200 to 4,500 it makes the grunt that you feel in everyday driving. However, you can see that the GT350 manifold is vastly superior at the top of the tach, as it takes the advantage just before 6,000 rpm and never gives it up. Comparing the Cobra Jet and tuned GT350 runs is a bit more complicated. The CJ gives up some performance at certain points in the midrange but also makes some schizophrenic gains there as well. Up top it offers double-digit gains from 6,100 to 7,200 but tapers off a bit as the rpm approaches 8,000. Ultimately the CJ is a little better than the stock GT350 intake, but not by the wide margin we had assumed going into this test.
very interesting