stroker Hemi combination equipped with TEA-ported 5.7L heads, a Comp XFI 260H cam and internals from JE, Scat, and Speedmaster, the long-runner truck intake easily outperformed the short-runner single-plane intake up to 5,800 rpm. For 5,800 rpm on up, the single-plane intake was tuned to optimize power production and offered 8 more peak horsepower, but the difference grew to 25 hp at 6,300 rpm. Intake manifolds are optimized for power production in specific rpm ranges, a point illustrated perfectly by this, and every other test in this chapter.
Despite being designed for low-RPM truck applications, this factory intake offered surprising power production.
The single-plane design was designed for high-RPM power and was a tad out of place on this mild 5.7L stroker.
Truck vs MP Single Plane for a 5.7L Stroker
Stock Truck Intake: 436 hp @ 5,700 rpm
MP Single Plane: 444 hp @ 6,300 rpm
Largest Gain: 25 hp @ 6,300 rpm
The horsepower curves show a number of things including the fact that the single-plane intake did indeed make more peak power than the long-runner truck intake. Measured peak to peak, the single-plane, carbureted intake produced 444 hp to the 436 hp offered by the truck intake. The difference was a healthy 25 hp out at 6,300 rpm, where the power output of the stock intake fell off rapidly.
Truck vs MP Single Plane for a 5.7L Stroker
Stock Truck Intake: 440 ft-lbs @ 4,800 rpm
MP Single Plane: 410 ft-lbs @ 5,000 rpm
Largest Gain: 40 ft-lbs @ 3,500 rpm
In terms of torque production, it was really no contest. The peak torque production between the two intakes differed by 30 ft-lbs, but the difference was as great as 40 ft-lbs elsewhere in the curve. The additional torque offered by the long-runner factory intake in the low and mid-range is why it is usually chosen over the single plane for most street (and production) applications. The truck intake bettered the single plane up to 5,800 rpm, where the majority of driving takes place.
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
