4.6L Cobra Intake Test: Stock vs. Kar Kraft (Weiand and Holley)
On the scale of 1-10 for good ideas, this Kar Kraft adapter system rates a solid 10. To increase the number of intakes available for the 4.6L by one or even two is a relatively simple thing. To increase the number available by 10 or 20 with one simple setup is difficult indeed, though all it took was one great idea and some fancy machining. With all the intakes available for the 5.0L motors, why not make a set of adapters to allow use of all those intakes on the mod motor? Using the adapter plates from Kar Kraft, we installed a simple setup in the form of a Weiand Stealth intake and Holley 750 HP carburetor. Running the Stealth intake and 750 HP carb, the motor produced 382 hp and 332 lb-ft of torque.
The Sullivan intake was also run with this four-hole throttle body from FAST; it was worth a few extra horsepower over the elbow. |  | 
After running the two EFI versions, we installed a Holley 750 HP carburetor on the Sullivan intake. With the FAST computer still in control of the timing curve, the Holley carb supplied the necessary fuel, and even managed to produce the highest peak number (436 hp) of the test. |
4.6L Cobra Intake Test: Stock vs. Kar Kraft (TFS Box R)
Wanting to run a 5.0L EFI setup on the mod motor, we selected the Box R manifold system from Trick Flow. Having had such success recently on our 408 stroker motor, we decided to give the impressive Trick Flow combo the nod over the many available options. Like the Weiand carbureted system, the Trick Flow Box R lower intake bolted right to the Kar Kraft adapters using a set of Fel-Pro 1250 intake gaskets. The Trick Flow Box R intake assembly looked right at home on the mod motor, though a scoop would definitely be in order for use under the hood of a Cobra. Equipped with the Box R feeding the Kar Kraft adapter plates, the 4.6L produced 394 hp and 355 lb-ft of torque. The Kar Kraft adapters are indeed a great idea, but we'd like to see them open up the port dimensions of the adapters to match the larger 1262 gaskets to further increase the flow potential. After all, the Four-Valve heads flow substantially better than a set of stock 5.0L heads.
Next up were these trick adapter plates from Kar Kraft. The plates were designed to allow the installa-tion of any 5.0L-based intake onto the Four-Valve motor. The ports were designed to mate to a Fel-Pro 1250 gasket, but we'd like to see a set produced to match the larger 1262 gaskets for some serious flow. | 
Using the Kar Kraft adapter plates, we installed a Weiand Stealth intake and Holley 750 HP carb. Equipped with the carbureted intake, the 4.6L produced 381 hp and 332 lb-ft of torque. | 
After running the carbureted 5.0L intake, we decided to try a fuel-injected version. The Trick Flow Box R was a natural choice and looked right at home on the Four-Valve Cammer motor. Running the Trick Flow intake, the 4.6L Cobra produced 394 hp and 355 lb-ft of torque. |
4.6L Cobra Intake Test:Stock vs. Custom Dual Plenum
The final intake tested on the modified Cobra motor was this adjustable, dual-plenum design whipped up by your author. Eagle-eyed readers will no doubt recognize it as the very one run on the 5.4L motor. How does one intake fit both the 4.6L and larger 5.4L motors? Isn't that like one intake fitting both the 302 and 351W motors? Actually, the Windsor scenario is pretty accurate, but the answer is quite simple. The base for this custom intake was built in two pieces, which allowed it to be run on either the 4.6L or larger 5.4L since there's nothing connecting the two halves that dictate a predetermined width. Like the manifold flanges, the runners and even plenums were separate, joined only by a (clamp-on) U-shaped junction at the rear. The adjustable nature of the manifold allowed us to run a variety of different configurations, which produced a variety of different power curves (and peaks). While we were able to produce as much as 436 hp (matching the carbureted Sullivan system), we selected a slightly longer runner length that produced a better overall torque curve. So equipped, the 4.6L produced 424 hp and 369 lb-ft of torque, bettering the stock intake from 5,500 rpm to 7,000 rpm. This combination matched the factory torque production from 3,000 rpm to 4,600 rpm, falling behind slightly to 550 rpm.
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Given its modular construction, we were able to employ the same adjustable intake run on the 5.4L test. Equipped with the custom dual-plenum intake, the test motor produced as much as 436 hp, but the best overall curve netted peak numbers of 424 hp and 369 lb-ft of torque. Like some of the others, this intake would certainly not fit under the stock hood. |  |