Super Intake Shootout

Not surprisingly, a 347 that produces more power than a 302 requires more intake flow to do so. Running the same intake lowers the rpm where the motor makes peak power. The difference can be as little as 100 rpm and as much as several hundred rpm, but there will be a difference. With the basics of the 347 test motor set for our journey beyond 6000 rpm, we finished it up with a number of other performance components. The ignition chores were handled by an MSD Billet (EFI) distributor and matching MSD coil. Once we had all the wiring hooked up properly to the EEC-IV, the motor ran the numerous intake manifold tests without a hitch. That is to say the MSD ignition components ran perfectly. In addition to the ignition, we fitted the 347 with a set of 13/4-inch long-tube Hooker headers. The exhaust was run open behind the headers save for a set of 14-inch collector extensions. We did not want to limit the power of the motor (or intakes) by limiting exhaust flow. The open headers and extensions allowed optimized exhaust flow for our intake manifolds. The motor was run on the SuperFlow engine dyno without any of the normal accessories (water pump, AC, PS, etc.). We elected to use a CSI electric water pump on the test motor to keep the water temperature stabilized during the hard dyno runs.

We have run literally hundreds of dyno pulls with the CSI electric water pump on numerous different 5.0-based motors and it has not complained once. Additional finishing touches to the 347 test motor included a high-volume oil pump, Coast High Performance deep-sump oil pan and matching pick up. The final element was a set of Comp Cams 1.6 ratio aluminum roller rockers.

Before running the 347 test motor with a GT-40 intake to establish a baseline, we needed to solve one important problem. The intake manifolds were scheduled to run with a stock EEC-IV computer, 36 lbs.-hr. fuel injectors and matching Pro M (calibrated) mass air meter, but we needed to figure out a way to exceed the 6250 rpm rev limit imposed by the factory computer. Our first thought was to call on the experts at PowerTrain Dynamics to burn us custom chips for each intake with the rev limiter removed. Since we were running a real-time air/fuel mixture meter on the dyno, each intake combination could be optimize by PowerTrain. Though this might have been a great way to go, we eventually decided against it for one very good reason. Most readers out there do not have access to a handful of custom (dyno verified) computer chips to fully optimize their 347 combination. Rather than take advantage of our ability to do just that, we decided to make the test more real world (what the average enthusiasts might actually have) and simply use the computer, calibrated meter and a Ford Racing Extender to probe the upper limits of the rev range on our test motor.

Not only did the Extender from Ford Racing solve our rpm problem, but it was also easy to use (a big benefit to enthusiasts). With only two different adjustment knobs, it was hard to get confused about the "programming" of our test motor. Basically, the pair of knobs on the Extender were to adjust the new rev limit and desired air/fuel mixture. Since the Extender adjusted the fuel tables based on a desired air/fuel ratio, we were required to hook up the two factory oxygen sensors to the dyno harness.

For our testing purposes, the rev limit dial on the Extender was set for 7100 rpm, while the desired air/fuel ratio was set conservative at 12.8:1. Though peak power will be much better at 13.2:1, we elected to adjust a conservative number to see how effective (and accurate) the Extender was at adjusting our air/fuel mixture.

We also had an Accufab adjustable fuel pressure regulator on the factory fuel rail to make further air/fuel adjustments. Though we relied on the timing table of the factory EEC-IV, we did maximize power by adjusting the static timing up to 16 degrees. Since we were using 100 octane unleaded fuel in our 11.5:1 347, we figured that 16* of static timing was plenty safe.

Once the motor was assembled and hoisted onto the dyno, we installed the GT-40 intake to begin the test. Unlike the three other three intakes run in the first part of this intake shoot-out, the GT-40 intake was not box stock. A modified GT-40 was run for two reasons. The first reason was that we figured that no enthusiast would run a bone-stock GT-40 on such a great motor. The second reason was that we had a couple of other GT-40-based upper intakes to test for the second part of our intake shoot-out and wanted to make sure they flowed as best they could. To that end, we elected to run a stock GT-40 upper intake on an Extrude Hone ported GT-40 lower intake to establish a baseline. The ported lower would come in handy later when we tested the Comp Cams box and modified Cobra upper intakes. Though the other three intakes (TFS R, Holley SysteMax II and Victor 5.0) were all run with the recommended 75mm throttle body, the throttle opening in the stock GT-40 upper was too small to run the 75mm throttle body. The GT-40 was tested with a 70mm throttle body.

After a few pulls to establish the air/fuel mixture and check out how well the Extender worked, the GT-40-equipped 347 was run right past the 6250-rpm factory rev limit all the way to 6600 rpm. With the GT-40, the 347 posted some impressive power numbers. The peak torque checked in at 447 lbs.-ft. at 4700 rpm, while the peak power reading of 450 hp was all the way up at 6600 rpm. Unlike other intakes, we could not load the 347 any lower than 3300 rpm. This was due to the torquey nature of the long-runner GT-40 intake. With our baseline in hand, we began our rev-happy intake adventure.

The next intake installed on the 347 test motor was the TFS R intake. As the top dog in the series of three offerings from TFS, the R series intake featured shorter and larger runners compared to its long-runner siblings.

The short runners with large cross-sections made it a perfect choice for our healthy 347 test motor. The runner specifications on this TFS R intake were quite similar to the other two desperadoes in this shoot out. Though we were most interested in the power curve generated by the three different upper and lower intake combinations, we also took into account the ease of installation and general finish of the contestants. The TFS R intake got high marks for cool factor as well as ease of installation.

Unlike the Holley, the six bolts securing the TFS R upper intake to the lower intake were accessible from the top of the manifold (similar in concept to the GT-40). This compares nicely to the Saleen /Vortech intake that requires a bit of dexterity and a custom tool to reach the mounting bolt positioned under the middle section of the plenum. One interesting note about the TFS R intake was that though the TFS literature called out for a 75mm throttle body, the opening in our intake was much closer to 70 mm than 75mm. It is possible that our intake (from Westech) was an early pre-production system that had not received the latest machining, but at any case, the throttle opening was somewhat smaller than expected. As it turned out, none of the intakes actually came with 75mm openings.