Mopar's 5.7L and 6.1L Hemi engines are certainly potent, but they haven't garnered the attention of hot rodders to anywhere near the level of GM's LS-series engines. That's too bad, since the new Hemi has a great deal going for it even in stock trim. Like the current LS3, the SRT8 Hemi is blessed with tremendous cylinder heads. Impressive even in stock form, the 6.1L SRT8 heads respond to precision porting every bit as well as the General's heads. A properly ported set of 6.1L Hemi heads (like the ones employed in this buildup from Dr. J's) can flow more than 350 cfm at just 0.600 lift. That is some serious head flow. The SRT8 version of the modern Hemi also sports an impressive factory aluminum long-runner intake, a sizable throttle body, and free-flowing factory exhaust manifolds. There are Hemi owners who think the 425hp factory rating is not only insignificant but downright pedestrian and think nothing about more than doubling the factory power output.
What does it take to exceed 1,000 hp with a 6.1L Hemi?
To demonstrate what it takes to produce an honest 1,000 hp with a new Hemi, we decided to take up the folks at Kenne Bell (K-B) and Mr. Norm's on their offer to test one of their massive, new, 3.6L, twin-screw superchargers on a 6.1L Hemi (destined for use in a new Mr. Norm's Super Challenger).
When it comes to superchargers, there are two schools of thought: run a small blower fast or a big blower slowly. Both have their benefits, but sizing the blower for the intended displacement, boost, and power levels is critical for success. Luckily for us, the twin-screw design of the K-B blower is ultraefficient, much more so than the typical Roots-style blower.
With the introduction of powerful engines like the 6.1L Hemi and the attending stroker variants, Kenne Bell recognized the need to increase the displacement and efficiency of its already impressive 2.8L supercharger. The improvements to the 3.6L compared with the previous 2.8L came from three major changes: an increase in displacement, liquid cooling, and seal pressure equalization. K-B also claims to have reduced the parasitic losses associated with driving the supercharger by a huge 76 hp. To put this into perspective, the 3.6L will produce the same amount of power as the smaller 2.8L blower at roughly 3 psi less boost. Some of the drop in parasitic losses can be attributed to the fact that the larger blower simply spins slower to produce the same amount of boost as the smaller 2.8L. Additional gains come from a revised 4x6 rotor pack, meaning the male and female rotors sport four and six lobes respectively, differing from the claimed less efficient 3x5 combination used by the competition. Changes to the rotor pack were combined with a unique discharge shape to optimize port timing, maximize airflow, and minimize charge temperature.
From a size standpoint alone, the new 3.6L is capable of supporting more than 25 percent more power than the 2.8L, yet it still fits under the hood of a Challenger. While the bigger-is-better philosophy seems like a no-brainer, the ideal application for the larger, 3.6L blower is not a stock 5.7L Hemi running 7 psi of boost but rather a 6.1L (or larger) running 15-plus psi of boost. The larger 3.6L Kenne Bell blower was designed for high-horsepower and/or high-boost applications. Given its ability to support 1,200-plus horsepower, it is less than ideal for someone looking to produce just 400 hp. The big blower will obviously do the job at lower boost and power levels, but there are better blower choices for the lower-horsepower applications.
Impressed as we were by all the technical features of the new, bigger blower, we wanted to see it applied to a 6.1L Hemi. Naturally, a stock 6.1L is not going to stand up to the abuse of 20-plus psi of boost, so the motor was built with forced induction in mind, using forged internals, ported heads, and a different camshaft. The combination in naturally aspirated trim baselined at 510 hp and 467 lb-ft, and adding the 3.6L blower set on big boost, it jumped that into the magical four-digit range, nearly doubling the power output to 1,003 and 881, respectively.
6.1L Hemi-NA vs. K-B 3.6L Blower
(22 & 24 psi)
Adding the new 3.6L twin-screw supercharger from Kenne Bell to our modified 6.1L Hemi resulted in serious power. Equipped with ported heads, a Comp cam, and long-tube headers, the 6.1L produced 510 hp and 467 lb-ft (bottom lines). Adding the Kenne Bell 3.6L supercharger kit upped the peak power numbers to 1,003 hp and 881 lb-ft at 22 psi and 7,000 rpm. Upping the boost pressure with a smaller blower pulley (from 3.75 to 3.50 inches) resulted in 24 psi of boost and a jump in peak power to 1,019 hp at just 6,500 rpm. More boost and/or more engine speed would certainly yield even more power, as would replacing the 6.1L short-block with a 392 or 426 stroker version.
