Published on

The Forgotten IR Intake Add 29HP And Lose Nothing Else!


The sad truth is, in terms of popularity, the modern Dodge Hemi takes a back seat to GM’s LS motor. If the Chevy is indeed the prom king, think of the Hemi as the guy in a leather jacket and tattoos who just crashed the party. Every bit as fit, the Hemi is just slightly less polished and proper, and real Dodge boys (and girls) would have it no other way. Yep, the Hemi is the bad boy of the bunch, and for good reason. Sporting the most recognizable name in the automotive industry, the modern Hemi had some big shoes to fill. The previous generations racked up countless wins in almost every form of motorsports, the most famous being those Top Fuel rocket ships. Even in stock trim, the 426 Hemis were serious contenders, ranking at or near the top of the performance heap during the original muscle car era. One needs to look no further than the auctions sites at the current pricing of Hemi-powered ’Cudas to see how much value enthusiasts place on the power of the pachyderm.

Lucky for modern Hemi owners, Dodge engineers haven’t been asleep at the wheel for the last four decades. The modern motor is arguably even better than the original, eclipsing not only the power production of the larger 426, but offering vastly improved fuel economy, mileage, and overall drivability. Compared to the current crop of modern rivals, the 6.4L (392) Hemi offers increased displacement and rated power output over both the 5.0L Ford and the 6.2L Chevy. The take away for this trip down memory lane is that the new Hemi is awesome, and deserves every accolade thrown its way. That said, even a good thing can be made better, especially if we are starting with a more pedestrian 5.7L instead of the 6.1L or 6.4L variety. The downdraft intake tested here will perform every bit as well (actually better) on the larger, more powerful combination, but this test clearly illustrates that every Hemi responds very well to the right induction system.

To illustrate the gains offered by the right induction system, we set up a simple test using a modified 5.7L Hemi crate motor. The 5.7L crate motor from Mopar Performance was augmented with ported heads, a .547-/.550-inch lift hydraulic roller cam and stronger beehive valve springs. The crate motor was originally equipped with a single-plane intake and four-hole (4150) throttle body. Designed as a retrofit combination for early muscle cars, trucks, or street rods, the 5.7L offered more than adequate performance, especially in modified trim. Run on the dyno with a Holley HP management system and Hooker headers, the 5.7L produced 483 hp at 7,000 rpm and 403 lb-ft of torque at 5,600 rpm. As expected of the single-plane design, the power production occurred higher in the rev range. The aggressive cam timing and ported heads obviously helped this situation along, but what this combination really needed was enhanced torque production. If we could get said torque without sacrificing top-end power production, so much the better.

Our quest for power led us to the individual-runner downdraft induction system offered by Speedmaster. The system came complete minus the actual ECU and harness, but we used the same Holley management system to control the timing and fuel curves. Where the single-plane induction system from Mopar Performance relied on the four holes in the 4150 throttle body, the downdraft system offered no less than eight 2.25-inch diameter runners. In terms of sheer airflow, the eight-stack more than doubled the flow potential of the 4150 throttle body, but the power gains were not simply from extra airflow. The big torque gains that occurred through the entire rev range came from a change in runner length. The short runners offered by the single-plane were optimized for power production at a much higher rev range than the downdraft. As such, the Speedmaster system was able to greatly enhance torque production through the entire tested rev range. Had we run the motor to 8,500 rpm, the single-plane may have gained ground, but up to 7,000 rpm, the optimized length offered by the downdraft system really shined.

Installation of the system was simple, as it bolted right in place. There was a slight mismatch between the opening of the runners and ported 5.7L cylinder heads, but obviously not enough to cause a loss in power. The system did feature provisions to equalize the all-important MAP sensor reading, as it was possible to combine the signal from every port. The center-pull linkage was easy to hook up and equalized side-to-side throttle opening. We’d like to see the TPS set up to accept the more common GM sensor, but once installed, we decided Hemi enthusiasts would likely be making their purchasing decision on looks alone. Few things rival the appearance of a Hemi with stack injection. After quickly dialing in the WOT fuel curves (plan on spending some time on cruise and drivability), we were rewarded with a jump in peak power to 512 hp, but more importantly, torque production was up to 452 lb-ft at 5,100 rpm. We liked the extra 29 hp, but we loved the extra 49 lb-ft of torque even more. Torque was up through the entire rev range, showing that this Hemi downdraft system from Speedmaster looked and cooked.

MP Single Plane vs Speedmaster Downdraft IR

It is likely the Speedmaster downdraft system sold itself even before you saw these dyno results, but the extra power is certainly some enticing icing on the performance cake. Equipped with the single-plane intake and four-hole throttle body from Mopar Performance, the modified 5.7L was no slouch, producing 483 hp at 7,000 rpm and 403 lb-ft of torque at 5,600 rpm. After installation of the individual-runner, downdraft system, the power numbers jumped to 512 hp at 6,600 rpm and a (relatively) massive 452 lb-ft of torque at 5,100 rpm. The combination of runner length and flow provided a sizable jump in not just peak power, but power production through the entire curve. This is the kind of dyno sheet you’d be proud to show your fellow fanatics at the local Cars & Coffee gathering.

 

Who wouldn’t want to replace the plastic factory induction system on their Hemi with this impressive performer from Speedmaster?


To maximize airflow, the Speedmaster’s downdraft system features full-radiused air horns. Each horn has the job of filling a single cylinder.


To ensure an accurate vacuum signal, the Speedmaster eight-stack also provides vacuum ports for each bank of cylinders.


To dial in the air/fuel and idle speed, each runner features a bypass adjustment screw.


The trick induction system also featured easy-to-install, billet-aluminum fuel rails designed for use with -AN fuel fittings.


The fuel rail was also designed to accept this adjustable fuel pressure regulator to dial in the static fuel pressure.


Our 5.7L Hemi crate motor from Mopar Performance was augmented with a set of ported heads.


The heads were also treated to a set of high-performance beehive springs. These improve valvetrain stability at higher lift due to less mass and more force.


No Hemi upgrade would be complete without a performance camshaft. Prior to testing, the crate motor received this hydraulic roller cam with .547/.550 inches of lift, a 224/228-degree duration split, and 114-degree LSA.


Since high rpm was in the cards, we upgraded the stock damper with this Super Damper from ATI.


Ensuring a hot spark for our intake test was a set of MSD coil packs.


We decided the polished eight-stack induction system deserved a little more bling. To add the necessary spice, we installed billet aluminum valve covers from Moroso.


Exhaust chores were handled by a set of Hooker 1 7/8-inch, long-tube headers designed for a Magnum application.


The 5.7L Mopar crate motor was supplied with this single-plane intake. Single-plane intakes were designed to enhance power production higher in the rev range.


Feeding the single-plane intake was this four-hole, 4150-style throttle body. Think of this as a carburetor that delivers only air without the fuel. It flows more than a comparable carburetor, since fuel does not displace any of the potential airflow.


Equipped with the single-plane intake and 4150 throttle body, the modified 5.7L Hemi produced 483 hp at 7,000 rpm and 403 lb-ft of torque at 5,600 rpm.


The one change we made to the Speedmaster downdraft IR system was to add a set of ACCEL 61 lb/hr injectors.


After installation of the Speedmaster eight-stack system, the power output jumped to 512 hp at 6,600 rpm and 452 lb-ft of torque at 5,100 rpm. Not just more power, but more power everywhere!