The Six Pack intake, like...
The Six Pack intake, like the Performer RPM, is a dual-plane design, cut with a unique plenum design to accommodate the three carbs that run the length of the engine.
Crunching The Numbers
For the baseline test, the engine was fitted with a Performer RPM intake, topped with a Holley PN 0-80511-1 carb-an 830 cfm rated HP-series carburetor actually produced for Winston Cup competition. Both the carb and intake are modern designs, and some of the best equipment available. Our Six Pack arrangement was up against some stiff competition. We loaded the 440 onto Westech's SuperFlow 901 engine dyno and began optimizing the engine timing and the jetting on the Holley carb. The best output achieved came to the tune of 535 hp at 5,300 rpm, and an unreal 581 lb-ft at 3,900 rpm. The average output over the test range from 3,000-5,600 rpm worked out to be 553.3 lb-ft, and 450 hp. The Six Pack would have to work its proverbial tail off to meet the baseline figures of the single Holley.
We had the manifold swapped to the factory-calibrated Six Pack setup in short order. For our baseline run, the carbs were run out-of-the-box stock. The numbers were down on what we had seen with the previous induction, but not by much. We had peak numbers of 531 hp at 5,300 rpm, and 569.7 lb-ft at 4,000 rpm. The averages were also down, showing 545.7 lb-ft and 445 hp-a loss of nearly 8 lb-ft and 5 hp average over the pull.
Step one when setting up the...
Step one when setting up the Six Pack is to check and adjust the float levels. The sight plug in the float bowl is removed, and the centrally mounted needle and seat is adjusted until the fuel just trickles past the sight hole's threads.
Was there a reason to be disappointed? To us, things were looking pretty good. The Six Pack proved much closer to our engine's top-dog induction than did some of the other intakes run in past testing. We were still box-stock on calibration. As a side note, those who are familiar with the Six Pack induction know the outboard carbs are actuated by large vacuum diaphragms mounted to the carbs, rather than mechanically through the throttle linkage. To ensure that the outboard carbs were fully opening, a backup pull was performed as a test with the carbs' linkage pinned for mechanical operation. The result was a near perfect overlay of the output curve generated in the previous dyno pull. There was no question about the secondary carbs opening.
Quickfuel Plates\
Since we were dealing with a well warmed-over 440, we had the issue of calibration to contend with. The stock Six Pack carbs come calibrated exactly as factory issued-designed to work on a mildly-cammed 390 hp 440 with iron exhaust manifolds and stock #906 or #346 heads. Extracting the potential of the Six Pack on our modified test engine would require jetting; however, the stock Six Pack carbs come with fixed-orifice metering plates in the outboard carbs. To facilitate making metering adjustments, a pair of QuickFuel's trick replacement metering plates were ordered. In lieu of jets, the factory-style metering plates use a drilled orifice for main-circuit fuel metering. Changing calibration can only be accomplished by drilling the metering orifices, or by installing plates with a different calibration. While it's possible to fine-tune a factory plate setup to razor sharp precision, the procedure is time-consuming and awkward, not to mention expensive, if a variety of differently calibrated stock-style plates are utilized. The clever QuickFuel plates replace the originals with a design that accepts standard Holley main jets. Once the carbs are converted to the QuickFuel plates, calibration changes are simply a matter of removing the float bowl and swapping jets.
Converting the carbs is a simple procedure. The float bowls are removed to access the stock metering plate, which is held in place with six clutch-head screws. Just unscrew the stock plates and replace with the QuickFuel plates and gaskets using the same fasteners. Regular Holley jets are then installed, and it's a done deal. Since the QuickFuel plates fit inside the float bowls like the originals, once the bowls are reinstalled there is no external evidence that the carbs have been modified. Jetting the outboard carbs requires removing the rear carb from the manifold for float bowl access, and the front carb bowl can be removed for jet replacement while the carb is bolted in place.
Idle mixture screws are at...
Idle mixture screws are at each end of the center carb metering block, as with a conventional Holley four-barrel, but the outboard carbs have these small idle mixture needles in the base plate. In the early production carbs, they were sealed with lead plugs.
The outboard carb's rate of...
The outboard carb's rate of opening is controlled by a vacuum diaphragm, which functions the same as a vacuum secondary four-barrel. The spring inside can be changed to alter the opening rate. On the dyno, the loading is much different than in a car, so changes are meaningless. We just double checked that they were opening.
As can be seen from this view...
As can be seen from this view down the throat of the carbs, the bore of the center carb is smaller than the outboards. The center carb, rated at 350 cfm, features a 131/416-inch venturi and 111/42-inch throttle plates. The outboard carbs are rated for 500 cfm with larger 191/416-inch venturi and 131/44-inch throttle plates. Two-barrel carbs are rated at a higher-pressure differential than four barrels, so the cfm flow numbers can't be directly compared. The center carb's bores are about the size found on a 550 cfm four-barrel, while the outboards share dimensions with an 850.
Our first run with the box-stock...
Our first run with the box-stock carbs netted 531 hp and just shy of 570 lb-ft of torque. Peak hp was down a touch, but torque took a bigger hit.
While the outboard carbs come...
While the outboard carbs come with fixed "jetting" metering plates, QuickFuel makes a conversion plate that takes standard Holley jets, greatly facilitating carb tuning.