As we admitted at the onset of this project, we had set some pretty ambitious goals for our Mild-Mannered Mauler; in fact, we were looking to cut new ground. To recap, the engine is a basic .030-inch over 440, a balanced assembly with a factory forged crank, and a set of short dome SpeedPro pistons, massaged for a final net dome volume of 11 cc. The engine combination's main goal was to produce power like a race piece, at the 600hp level, and yet deliver road manners, idle quality, and an rpm range typical of a mild street mill. To put numbers on it, we were after 600 hp, 600 lb-ft, and an rpm range making peak at or just above 6,000 rpm. The idea was minimal bark, but a bloody bite in a normally aspirated package. This engine will eventually wind its way into a street 'Cuda convertible project, where it will be expected to idle with 13.5-14 inches of vacuum, and cruise the open road cleanly at low-to-moderate rpm with a deep overdrive ratio manual trans. It will need to sit in traffic in the heat of summer with the A/C on. Good fuel economy, quiet operation, and low maintenance would be nice too.
Taking an analytical look at those numbers, crossing the 600hp mark by itself isn't too tough with a good 440, but making it by 6,000 rpm is something that would take an outstanding execution of the combination. Remember, horsepower is derived from torque and rpm, so setting a relatively low cap on the rpm at which peak power will occur means it will take tremendous torque to get there. Making a peak torque number of 600 lb-ft from 446 cubes is really pushing the limits of what is obtainable. It can and has been done, but it's ground not often traveled. Add in the driveability and idle quality requirements, and it's going to be a development effort to get there.
The outline for meeting these requirements was pretty clear: high airflow, short duration/high lift cam/ high compression ratio and cylinder pressure. Airflow had to be exceptional for good cylinder filling, especially with the short camshaft duration required to meet the rpm and driveability objectives. A long duration cam would make more power from the combination, but would sacrifice idle quality. We needed relatively short duration, and would make up for the short overall timing with exceptionally fast valve opening rates and high lift. In theory, the super-aggressive Competition Cams XEHL hydraulic lobes would provide the fastest valve action, and as a hydraulic would meet the low-to-no maintenance and noise objectives. Working with custom 1.7:1 rocker arms, the combo we settled upon delivered .600-inch net lift, with a rated duration of only 275 degrees at .006-inch lift, or about the same overall duration as stock. A single pattern cam set on a 112-lobe separation angle, and installed at 106-degrees intake centerline would help achieve an idle not much off a near-stock 440 Magnum, despite the lift.
High compression would serve double duty, helping to achieve the torque and power numbers we targeted, while the reduced clearance volume also aids in cleaning up the idle. Modern OEM engines are pushing ever closer to the 11:1 mark, with Chevrolet's new LS7 Corvette plant actually at that level now. Initially, we were shooting for about 11.7:1 compression, and we had prepped a set of Mopar aluminum heads for the job with 88cc chambers. We were confident that compression ratio could be tolerated on pump gas with thermal barrier coatings, a tight .035-inch quench, and cold-air induction. Midstream, the highly modified Mopar head castings were set aside in favor of Indy's CNC-ported 295cc EZ heads, which featured better flow and a more workable architecture.