Muscle Mustangs & Fast FordsHow To Engine
Super Intake Shootout
Damn the tachometer--full speed ahead!
Just out of curiosity, I took down several of my big boxes of back issues of MMFF, and thumbed through just about every Mustang magazine for the past six to seven years in search of intake manifold comparisons. I'm talking about one heck of a lot of magazines to go through, as my search even included tests run by the competition (other Mustang magazines). After my exhaustive search, I came across a familiar trend. The vast majority of the intake manifold testing for any 5.0-based motor configuration (strokers included) has been run with one of several major handicaps, but as we shall see, the handicaps were there by design. Though it is likely that every conceivable intake available for the 5.0 has been subjected to the rigors of the dyno, in all the tests (even those run by yours truly) there was almost always something left on the table.
In the beginning, there were ported stock H.O. intakes, followed shortly by the vastly improved GT-40. The GT-40 was and continues to be the aftermarket intake that all others are measured by. This particular test is no different, as we elected to run our test motor with a GT-40 before running the remainder of the intakes. After the Ford Racing GT-40, the aftermarket began building any number of upper intakes (some may actually predate the GT-40) and then manufacturers jumped in whole hog and gave us the overwhelming conglomeration of intakes now available for the 5.0 (and 5.8 variants). In looking at the available intakes, the vast majority are of the long-runner variety. Sure, box uppers such as the Comp Cams polymer, Downs and Hurricane uppers are available for a variety of different lower 5.0L manifolds, but the Performer (& RPM), Cobra and Trick Flow Specialties Street manifolds tend to be the most popular due to their long-runner design, which offers an abundance of usable power in the rpm most often seen on the street. With gobs of torque and a power curve that peaks between 5500 rpm and 6000 rpm, the long-runner intakes are tough to beat for street and most strip applications.
Let's face it, the long runner intakes make the most sense for the vast majority of 5.0 applications for another related reason. The vast majority of motors out there prowling the streets are of the hydraulic-roller persuasion. A marvel of technology that combines excellent friction reduction with set-it-and-forget-it adjustment schedules, the hydraulic roller cam has a lot going for it. The hydraulic roller valve train is also one of the limiting factors to power and the reason to choose an intake that signs off at 6000 rpm. Given the relatively hefty weight of the hydraulic roller lifter, the system is not designed to run much above 6000 rpm without experiencing lifter bounce (not quite the same as rpm-induced valve float). Look for a detailed examination of this phenomenon in a later test and possibly even a cure that will allow extended revs (not added spring pressure) from the good folks at Comp Cams in a future issue. For now, simply accept the fact that a hydraulic roller lifter is limited to somewhere near 6000 rpm, plus or minus a few hundred rpm.
In most street and strip 5.0 applications, a 6000 rpm ceiling on power is both more than sufficient and a blessing in disguise. Given the fact that supercharged motors have produced in excess of 700 hp at 6000 rpm, there is obviously plenty of power to be had from a 5.0 or stroker version even with the near-6000 rpm rev limit. Keeping the revs near 6000 rpm also makes life much easier on parts, as engine life decreases dramatically with increased engine speed. Keeping the parts alive should be paramount to any 5.0 enthusiast. The valvetrain induced 6000-rpm rev limit (please, no letters about the 6250 factory rev limiter or how your motor revs to 7000 rpm with hydraulic roller lifters) works perfectly with a long-runner intake to produce an exceptional torque and horsepower curve, usually peaking just short of 6000 rpm. Given the perfect match of valvetrain dynamics and long-runner intakes, what more could you ask for?
What more, indeed? Don't racers and enthusiasts alike always ask for more?Not long after the long-runner intakes became available, short(er) versions were soon offered. Edelbrock gave us the long-runner Performer and Performer RPM versions, but soon stepped up with the Victor 5.0 version that offered much more rpm capability than our 6000 rpm motors could effectively use. The same scenario was true at Holley with the SysteMax II not to mention TFS and its R-series intake. Previous intake comparison tests revealed that, like the box uppers bolted to a ported lower, these race manifolds were just getting started when shut down at 6000 (or 6250) rpm. More often than not, a comparison between these intakes and a GT-40, Cobra or Performer RPM resulted in the race intakes taking a back seat to the "smaller" street-oriented manifolds.
The reason was not so much that the race intakes lacked air flow or power potential but that the test parameters were all stacked in favor of the long(er) runner, street intakes. Running a TFS R, Holley SysteMax II or Victor 5.0 intake on a stock or even a mild 5.0, especially one with a hydraulic roller valve train is an exercise in intake misapplication. The result would be that the motor runs out of revs before it runs out of intake. Installing the same intake on the correct motor combination is a whole 'nother matter. Or is it?
What these performance-oriented intakes needed in order to strut their stuff was a test motor that had the power output to tax their flow capability and the rpm potential to find a peak power number. Basically, these intakes needed a real motor!
To properly run this intake test, we built just such a motor. Since the best way to produce horsepower is with displacement, we opted to start not with a 302 but rather with a 347 short-block. The 347 was assembled by Coast High Performance and featured a steel crank, h-beam rods and forged pistons. The displacement combined with the piston design and milled Air Flow Research 185 heads produced a 11.5:1 static compression ratio.
Having run the AFR heads on a 392 that produced 535 hp, we were confident that they would provide plenty of power potential for our intake test. Since several of the six different intakes would likely take the engine well beyond 6000 rpm, we needed a cam that offered a powerband that didn't peak below that figure. Knowing that revs were in our future, we ditched the hydraulic roller valve train and went straight for one of the solid roller profiles in the Comp Cams catalog. Wanting plenty of cam to tax the intakes, we selected the biggest, baddest, solid Xtreme Energy Street Roller profile offered by Comp Cams. The XE292R offered a 254/260 duration profile (at .050), a .621/.627 and a 110 lobe separation angle. Though a Street Roller, this was one healthy cam (too healthy for our piston-to-valve clearance, as we would later find out).
The cam, heads and even displacement were all chosen in an effort to basically optimize the motor for the three "Super Intakes" used in the first part of our two-part intake test. Designed to make peak power higher than their longer-runner relatives (Victor vs. Performer, TFS R vs Street and SysteMax II vs. I), these intakes required just such a motor to demonstrate their true worth. The AFR 185 heads offered plenty of airflow, while the cam offered plenty of rpm potential.
The final ingredient in our test motor was added displacement versus a typical 302. How does the displacement effect rpm potential and intake tuning you ask? Without a detailed explanation that might well run into several more pages, an intake used on a 302 will make peak power higher than an identical 347. For instance, a GT-40 used on a 302 will make peak power higher than on a 347. The added displacement tames the cam profile and requires more airflow as it produces more power. The flow rate of the long-runner intake becomes taxed sooner in the rpm band on a 347 than an identical 302.