offered as the production manifold on the 5.7L Hemi trucks to begin with. Measured peak to peak, the magnum bettered the truck intake by more than 20 ft-lbs, but the differences were even larger elsewhere along the curve.
Test 3: Stock vs Kenne Bell Throttle Body Test on a KB Supercharged 6.1L
About the only thing better than a modified Hemi is one with a supercharger. Nothing adds zing to a Hemi like boost from a Kenne Bell, twin-screw supercharger. As efficient and powerful as twin-screw kits are, boost is only the beginning. The reality is that superchargers are only as good as their induction system. Nothing chokes off the power potential of a supercharger faster than a restrictive throttle body or associated inlet components. Knowing this, the question now is how much power is a throttle body upgrade really worth? As an airflow device, the power gains offered by the flow restriction inherent in the stock inlet system depend on the modified power output. What this means is that the more powerful the engine, the more restrictive the stock components become. This should not come as a big surprise because the factory inlet system and throttle body were never designed for the elevated power levels offered by a Kenne Bell supercharger. The inlet system that Dodge designed to support 425 hp has no business on a supercharged engine making 600, 700, or even 800 or more horsepower.
It is important to stress here that when it comes to the power gains in part produced by the throttle body, the gains are dependent wholly on the engine combination. As a simple airflow device, the higher the power output of the test engine, the larger the throttle body required. As an example, installation of a larger throttle body (with airflow) capable of supporting 1,000 hp will be of little use on a 425-hp 6.1L engine equipped with an already oversized throttle body capable of supporting 750 hp. The 750-hp throttle body is already oversized for the application, so there is no need to upgrade on the naturally aspirated engine. A larger throttle body may be necessary on (draw-through) supercharged applications in which elevated power levels are more commonplace. While naturally aspirated Challenger engines with 600+ hp are less common, supercharged 6.1Ls exceeding 600, 700, or even 800 hp are everywhere. This round of testing on a Kenne Bell supercharged 6.1L illustrated that a throttle-body upgrade on a 770-hp application (17.3 psi) was worth an impressive 54 hp. Performing the same test on a stock (naturally aspirated) Hemi might be worth nothing.
To maximize airflow into the supercharger, we compared the stock throttle body to this 168-mm throttle body offered by Kenne Bell.
Run on the dyno with the stock 80-mm Hemi throttle body, the supercharged 6.1L produced 770 hp at a peak boost pressure of 17.3 psi.
Stock Throttle Body vs Kenne Bell Throttle Body for a Supercharged 6.1L
Stock TB: 770 hp @ 6,000 rpm
KB Oval TB: 824 hp @ 6,300 rpm
Largest Gain: 55 hp @ 6,300 rpm
Obviously the stock throttle body was plenty restrictive at this elevated power level on the supercharged 6.1L. Replacing the stock throttle body and adapter on the Kenne Bell supercharger with the larger 168-mm oval throttle body resulted in a jump in boost of 3 psi. This improved the power output of the supercharged 6.1L Hemi by as much as 55 hp.
Stock Throttle Body vs Kenne Bell Throttle Body for a Supercharged 6.1L
Stock TB: 781 ft-lbs @ 4,200 rpm
KB Oval TB: 801 ft-lbs @4,300 rpm
Largest Gain: 34 ft-lbs @ 5,400 rpm
Typical of airflow improvements, the gains were most prevalent at higher engine speeds. The throttle body change increased the boost pressure by 1 psi down at 3,500 rpm, but the torque gains were as high as 34 ft-lbs higher in the rev range. More flow into the blower equates to more boost out of the blower. A throttle body swap such as this may be worth nothing on a stock engine, but airflow is critical on a high-horsepower, supercharged application.
Test 4: Stock SRT8 vs Mopar Performance Single Plane for a 5.7L Crate Hemi
Much like the comparison in Test 1, this test involved a substantial change in runner length. If you are interested in a graphic representation of the change in runner length, check out the results of Test 8, where the only change was runner length (good stuff). Although there was a distinct design difference between the Mopar Performance single-plane intake and the factory SRT8 intake, the major difference was the tuning effect offered by the difference in the intake runners. The single-plane design featured not only significantly shorter runners, but uneven lengths for the various cylinders (actually pairs of four). This means that four of the cylinders will be tuned for one RPM range and the other four will be tuned for another. Specifically, the longer (outer) pairs will be tuned for a lower engine speed than the four (shorter) inner runners. By contrast, the SRT8 intake featured consistent runner lengths that ensured even power production from all cylinders.
The test was run on a 5.7L Hemi crate engine from Mopar Performance. The MP crate engine was equipped with a Comp 273 cam, long-tube headers, and a Holley 750 HP carburetor with the MP single-plane intake. The STR8 was run with a FAST XFI management system and 60-pound injectors. The comparison was less about carbs versus computers. The carb version of the MP intake made slightly more power than the port-injected, EFI configuration. Equipped with the MP single-plane and Holley carburetor, the 5.7L Hemi produced 469 hp at 6,500 rpm and 411 ft-lbs of torque at 5,300 rpm. Torque was not the single plane’s strong suit, but it did produce a healthy peak power number. After installation of the SRT8 intake, the peak power dropped to 455 hp at 5,700 rpm, but torque jumped to 450 ft-lbs at 4,800 rpm. The MP offered 14 hp on the big end, but lagged behind the SRT8 below 5,800 rpm.
Swapping intakes on the Hemi was fast and easy. The SRT8 offered exceptional power up to 6,000 rpm. The short-runner single-plane design excelled at top-end power production but fell short below 6,000 rpm.
Stock SRT8 vs MP Single Plane for a 5.7L Crate Hemi
Stock SRT8 Intake: 455 hp @ 5,700 rpm
MP Single Plane Intake: 469 hp @ 6,500 rpm
Largest Gains: 20 hp @ 6,600 rpm
Looking at just the peak numbers, we see that the single-plane intake offered more power than the factory SRT8, but that isn’t the story
