About 10 minutes after fuel-injected 5.0 Mustangs rocketed intopopularity in the late '80s, box intake manifolds appeared. These wereupper intake boxes that roughly resembled an elongated shoe box or loafof bread and were bolted to the existing lower intake. Some weredesigned for the stock oval-runner lower intake, while others mated tothe "staggered-round" GT-40 lower.
The idea behind these intakes was simple. By reducing the long upperintake runners to mere stubs and fitting a blimp-hangar-like plenumarea, screaming top-end power would result. True, their designersrealized, torque and midrange power would be greatly reduced, but withunheard-of top-end power, the "box uppers" would make up for theirmissing torque with gears and top-end horsepower. These intakes werenever designed for bolt-on-type cars that absolutely require runnerlength for reasonable torque in the real world. In fact, theirapplication was mainly intended for supercharged drag engines whereblower boost would make the day starting in the midrange.
Three inches of runner length...
Three inches of runner length is the key feature of Trick Flow's newBox-R Intake Manifold. It really shows here in this upside-down viewof the assembly, along with the 90mm throttle body opening. Total runnerlength with this upper and an R-Series lower intake manifold is 9 incheson a 302 and 10.3 inches on a 351.
You'll notice you don't see many of these early box intakes aroundtoday. We could be trite and say they didn't work, but that's only ahalf-truth. The thinking behind the box intakes was sound, but theexecution always left insufficient runner length for the street. Theresult was a near total loss of low-end torque, enough so that thetop-end power bonanza wasn't enough to make up the lack of low-endpower.
Horse Sense: Of course, we know about TrickFlow's cylinder heads and intake manifolds, but the company has alsoexpanded into several other product lines. These include intake spacers,valve covers, cams, diff girdles, 4.6 intake elbows, and even nitrouskits.
Keep in mind the early box intakes were designed for the stock or GT-40intakes. The straw-runnered stocker was a nonstarter in this category,and even the otherwise great GT-40 didn't have large enough or straightenough runners to be a top-end star. But that's what was available inthe early years.
Furthermore, enthusiasts insisted on bolting the boxes to bolt-on carsor mildly boosted street drivers with predictable results. The badmouthing from these ill-advised, dissatisfied street stormers didn'thelp. Yet another factor was the lack of cubic inches. Early on, the 5.0phenomenon was a 302ci party. The 347s were still in the future, andwhile a few souls had transplanted 351 Windsors into their Foxes, thewidespread use of 392s and 408s was also years away.
One place where the box intakes did well was on forced-induction cars atthe dragstrip. There the combination of steep final drive gears, a dutycycle comprised solely of high rpm, and--most importantly--a bigsupercharger positively cramming the intake full of air ensuredsparkling top-end performance and enough midrange to make a go of it.
As the photos show, a new box intake from the airflow experts at TrickFlow Specialties has reached market. Again, the idea is to promotehigh-rpm horsepower on big-inch 347 and Windsor-based strokers, but thistime more development has gone into the runner length, the plenum shape,and other details to make this a superior performer.
Looking inside the production...
Looking inside the production Box-R Intake Manifold plenum shows allsorts of good airflow features. The runners are evenly spaced and givenstraight runs to the lower intake manifold, and the air entry into therunners is smoothed and raised off the plenum floor. The O-ring sealbetween the upper and lower plenum castings is supplied by Trick Flow. Along section is provided, which easily lays into the groove, and then istrimmed to fit. The two-piece upper makes port-matching the upper to thelower a cinch.