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 here. 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