Test 2: Stock Truck vs Stock Magnum Intake for a 5.7L Stroker
In what will become a recurring theme, this test was run on two factory intakes that offered not just different designs for the different vehicles, which includes Magnum and truck, but represented significant changes in runner length. Since runner length determines where in the RPM range the intake was designed to promote power, choosing the right runner length for your Hemi application (and intended usage) is very important. Every bit as important as the runner length is the application; changes in things such as cam timing and displacement can determine the optimum intake design. For this test, we assembled a 5.7L stroker that displaced 370 ci. Thanks to a forged crank from Scat combined with rods from Speedmaster and forged pistons from JE, the stroker was ready for anything we could throw at it. For this test, the Hemi was equipped with a mild Comp XFI 260 H-13 cam that offered a .522/.525 lift split, a 208/212-degree duration split and 113-degree lobe separation angle (LSA). In addition, a set of ported 5.7L heads from Total Engine Airflow was part of the recipe. In addition to the porting, the Hemi heads received a valve spring upgrade from Comp Cams.
The stroker was used to compare a pair of stock intake manifolds. Both the factory truck and Magnum intakes offered long runners to promote torque production, but which one of them was best? Before testing, it was necessary to make a few minor changes to a couple of the factory components. First, we had to convert the drive-by-wire throttle body to manual operation. The next hurdle was to mill down the truck front cover to allow installation of the Magnum intake. The truck and Magnum 5.7L Hemis featured different FEAD mounting and therefore different front covers. The truck cover interfered with the position of the throttle body on the Magnum intake. A few minutes on the mill was all that was necessary to produce the desired clearance. Run with the truck intake, the Hemi stroker produced 436 hp and 440 ft-lbs of torque. After installation of the Magnum intake, the stroker produced 434 hp and 463 ft-lbs of torque. Despite a 2-hp deficit in peak power, the Magnum was the clear winner as the intake design offered a dramatic increase in torque production up to 5,400 rpm, with gains as great as 35 ft-lbs.
For this test we converted the electronic, drive-by-wire throttle body to mechanical operation. This allowed us to use a FAST XFI stand-alone management system.
Equipped with the Magnum intake and manual throttle body, the 5.7L stroker produced 434 hp and 463 ft-lbs of torque.
Stock Intake Shoot Out-Truck vs Magnum with a 5.7L Stroker
Truck: 436 hp @ 5,700 rpm
Magnum: 434 hp @ 5,800 rpm
Largest Gain: 22 hp @ 4,300 rpm
Tested on this mild 5.7L stroker application, there was little to choose from between the truck and Magnum intakes in terms of peak power. Although the peak numbers were within a couple of horsepower of each other, the curves differed dramatically before the power peak. The Magnum intake offered considerably more power through the majority of the rev range, up to 5,400 rpm.
Stock Intake Shoot Out-Truck vs Magnum with a 5.7L Stroker
Truck: 440 ft-lbs @ 4,800 rpm
Magnum: 463 ft-lbs @ 4,200 rpm
Largest Gain: 33 ft-lbs @ 3,500 rpm
The torque curve shows the real difference between the truck and Magnum intakes. The dramatic difference in torque production offered by the Magnum intakes makes us wonder why it wasn’t 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