Dodge Challenger - Hellacious Hemi

It's no surprise that the new Hemi is an impressive power plant, and a worthy successor to its legendary namesake. From the pedestrian 5.7 all the way up to the new 6.4, the Hemi is more than a match for anything offered by Ford or Chevy. Credit goes to the cylinder heads and an efficient intake design for the majority of the power. The tremendous flow rate of the heads and intake allow the factory Hemi to produce prodigious power with mild cam timing. The Hemi is literally begging for more aggressive cam timing, but fuel economy, emissions and idle quality concerns all dictate mild cam timing for factory engines. Given the airflow potential, one route to improved factory performance is increased displacement. Chrysler took this route with the new 6.4 Hemi to the tune of 475 horsepower. If 400 is good, then 800 horsepower must be even better, and the only thing better than 800 is 1,000 horsepower. Are you starting to get the picture?

Time and technology have marched on, and it seems that 1,000 hp is the new 500. Some might argue the necessity of 1,000-horsepower street cars, but the additional power is always useful given the excessive curb weight of Hemi-powered machinery (our Challenger tipped the scales at a portly 4,610 pounds! It takes a ton of power to get anything that heavy moving with authority, so the guys ST Motorsports set out to build one hellacious supercharged Hemi. The horsepower goal was an honest 1,000 (flywheel) horsepower, but every bit as important was the fact that said four-digit power plant must also double as a street machine. Race fuel was not eliminated as a track option, but suitable street manners were considered mandatory. With Kenne Bell's involvement, supercharging was a given, but 1,000 horsepower doesn't come from boost alone. The elevated power goals required attention to every component of the proposed power plant.

Normally aspirated engines run at atmospheric pressure. It is the pressure differential between the cylinder and outside air created by the downward moving piston that fills the cylinder. Superchargers enhance this cylinder filling-ability by increasing the pressure differential. Under the right circumstances, doubling the pressure supplied (14.7 psi of boost), can double the power output. A portion of this power is lost to drive the supercharger, but boost enhances the power output of the normally aspirated combination. The great thing about boost is that applying 14.7 psi can nearly double the power output of the normally aspirated combination, irrespective of the original power output. Thus, it should be obvious that a great supercharged combination always starts out as a healthy normally aspirated engine. The more powerful the normally aspirated combination, the greater the output offered by the supercharged configuration at any given boost level. Using this logic, it is much easier to reach a given power level at a reduced boost pressure. Lower boost levels (usually) increase blower efficiency and decrease inlet air temperatures (further increasing power), which in turn reduces the likelihood of harmful detonation.

Obviously, Adam Montague at ST Motorsports www.spankintime.com) understood this simple principle before starting the build. The first order of business was to build a Hemi capable of withstanding the 20-plus psi of boost that it was going to take to achieve the power goal. Stock Hemis are tough, but not 20-plus psi of boost tough. Starting with a 6.1, the first order of business was to increase the displacement. When it comes to power production, bigger is obviously better, so the 6.1 was punched and stroked out to 6.4 liters (393 inches) courtesy of a 3.795-inch SCAT crankshaft www.scatcrankshafts.com), 6.20-inch K1 rods www.k1technologies.com), and a set of 4.06-inch forged pistons from CP www.cp-carrillo.com). The forged rotating assembly increased both strength and displacement, which are both welcome when searching for 1,000 hp. Naturally, balancing, new rings and bearings were all part of the program. When completed, the assembled short block featured a 10.6: static compression. Some might consider this a tad on the high side for forced induction, but the reality is that the compression improves both (off-boost) mileage and power. Since all high-boost runs were made on race fuel, why give away the horsepower by dropping the compression a point or two?