Is a small gain in peak power better than having more power through the rest of the curve?
Stock SRT8 vs MP Single Plane for a 5.7L Crate Hemi
Stock SRT8 Intake: 450 ft-lbs @ 4,800 rpm
MP Single Plane Intake: 411 ft-lbs @ 5,300 rpm
Largest Gains: 41 ft-lbs @ 4,800 rpm
As much as we love an extra 14 hp, we love extra torque through the entire rev range even more. The torque curves illustrate the real difference between the SRT8 and the single plane; the factory long runners offered considerably more torque (both peak and average).
Test 5: Stock SRT8 vs Wilson Billet Intake for a Modified 6.1L
Some tests we run to illustrate what works, some we run to illustrate what doesn’t, and some we run just because the performance component under scrutiny is just so amazing. The test on this Keith Wilson Hemi intake falls into two of these categories. Once again, we applied the intake to a mild test engine similar to ported heads in Test 1 of chapter 2. The billet intake offered by the flow wizards at Wilson manifolds was significantly more intake than the mild 6.1L could utilize. We have seen these intakes on some of the most powerful Hemi combinations on the planet (usually with boost). The misapplication of the intake was by design because it shows there is a proper engine combination for every intake and our mild engine was not the ideal choice for the billet piece from Wilson. The second category this intake falls into is that it is a billet intake and looks like a piece of art when you pull it from the box. That alone is reason enough to want one, but knowing it comes from Wilson provides added confidence that the amazing form follows function.
We wanted to test the Wilson intake but didn’t have a 1,500-hp, twin turbo Hemi handy, so we ran what we had available. In this case, it meant we tested a modified 6.1L Hemi built for (eventual) boost supplied by a Kenne Bell. The 6.1L block was machined and treated to forged pistons from JE and a blower-proof ring package from Total Seal. Comp Cams supplied the XFI 273H-14 cam that offered a .547/.550 lift split, a 224/228-degree duration split and 114-degree LSA. A FAST XFI/XIM management system was used for all testing, while the guys over at Dr. J’s ported the 6.1L heads. All testing was run with American Racing long-tube headers with 18-inch collector extensions and no mufflers. Run with the factory SRT8 intake, the 6.1L produced 491 hp at 6,200 rpm and 453 ft-lbs of torque at 5,100 rpm. After installation of the Wilson intake, the peak numbers jumped to 510 hp at 6,800 rpm and 451 ft-lbs at 5,100 rpm. Once again, the shorter runners in the Wilson design offered more peak power at higher engine speeds (where race engines can take advantage of the extra power), but what the intake really needed was more cubic inches and some boost.
It was designed by the factory for this application, so it is not surprising that the SRT8 offered a good combination of average and peak power production on the 6.1L test engine.
If nothing but the best will do for your Hemi buildup, look no further than the Wilson billet manifold.
Stock SRT8 vs Wilson Billet for a Modified 6.1L
Stock SRT8 Intake: 489 hp @ 6,200 rpm
Wilson Billet Intake: 510 hp @ 6,800 rpm
Largest Gains: 19 hp @ 6,500 rpm
The Wilson billet intake easily bettered the factory SRT8, and (unlike other designs) did so without any significant losses in low-speed power. What the Wilson intake needed was actually more engine.
Stock SRT8 vs Wilson Billet Intake for a Modified 6.1L
Stock SRT8 Intake: 453 ft-lbs @ 5,100 rpm
Wilson Billet Intake: 451 ft-lbs @ 5,100 rpm
Largest Gains: 16 ft-lbs @ 6,500 rpm
In terms of peak torque production, the two intakes were within 2 ft-lbs of each other; the Wilson design came on strong after the torque peak.
Test 6: Single-Plane vs Edelbrock Dual-Quad Intake for a Modified 5.7L
This test was as much about the intake manifold design as it was about the method of fuel delivery. In this test, we compared an Edelbrock Dual-Quad intake with a pair of carbs to a single-plane intake with a 4-hole, EFI throttle body. The test engine was your basic 5.7L Hemi equipped with the usual modifications. The Mopar Performance crate engine was augmented with a new cam and ported heads. The original cam provided with the crate engine was replaced by an XFI 273H-14 grind from Comp Cams. The healthy XFI cam offered a .547/.550 lift split, a 224/228-degree duration split and 114-degree LSA. The cam required the use of a set of 26918 beehive springs and 762 retainers to provide the necessary coil-bind clearance and RPM capability. The last thing you want is to limit the performance of your cam with valve float. To ensure adequate flow for the new power potential of the modified engine, the stock 5.7L heads were given the once over by the guys at Total Engine Airflow.
Having run it on a number of other occasions, we knew what to expect from the MP single-plane intake provided with the crate engine. The design offered plenty of peak power (479 hp at 6,900 rpm in this case), but often lacked torque production lower in the rev range. The peak torque production of 404 ft-lbs at 5,300 rpm only hinted at the limited mid-range power production, but it became much more evident after we installed the dual-quad intake from Edelbrock. Not just any dual-quad intake, Edelbrock designed a dual-plane, RPM Air Gap, dual-quad manifold for the late-model Hemis. The new intake was designed to accept a pair of 500-cfm Edelbrock Thunder Series AVS carburetors. As we have come to expect from their namesakes, the Air-Gap design promised plenty of performance by isolating the charge air from contact with the heated engine. The real key to the power production was the dual-plane design. After installation of the Edelbrock dual-quad Hemi intake and carbs on our test Hemi, the peak horsepower output dropped slightly compared to the racy single plane, but was still adequate at 463 hp at 6,600 rpm. The peak torque output jumped, however, to an impressive 420 ft-lbs of torque at 4,900 rpm. The dual-quad intake outperformed the single plane up to nearly 6,000. Now toss in the cool factor and you have some very compelling reasons to top your Hemi with a trick induction system.
