The business end of this Hemi...
The business end of this Hemi head sports a massive 170cc CNC-machined combustion chamber. An even dark tone verifies that the flame and fuel travel is even throughout the chamber with no washed-out spots. Unlike their Top Fuel cousins, dual spark plugs aren’t required here.
Camshaft choice can be a tricky deal in itself, but when it comes to choosing a bumpstick for a Hemi, things get even tougher. Normal Wedge heads have the valves side by side, unlike the Hemi-style heads, which have the valves directly in line with each other. And the Hemis have a ton of exhaust flow compared to a Wedge head. That means the Hemi doesn’t need as much exhaust duration to get the job done. It also doesn’t need as much overlap for the exhaust scavenging pulse to help draw the fresh intake charge in. Quite often, as in Corey’s case, the cam will end up with the same duration on the intake and exhaust. By merely shortening the exhaust duration in relation to the intake, but keeping the intake centerline and the exhaust centerline in the same locations, there are two benefits. First, the exhaust valve will open later giving the burning fuel more time to push down on the piston. Second, closing that exhaust valve sooner decreases the amount of overlap and reduces wasted air and fuel going out the tailpipe.
In dyno testing different cams, Corey told PHR: “I’ve had them ground at 110- and 114-degree lobe separation, and 110 is going to give you a bigger peak torque number typically, but when the engine starts to fall off, it will fall faster than a 114-degree lobe separation cam. So if you’re going to be operating at 7,000 or 8,000 rpm, you’d definitely want to open that thing up, and I would be at least 114—and maybe 116 degrees—and flatten that curve out. It becomes like a tabletop at that point. But it typically won’t be as big of a peak torque number as if you were running something a little bit tighter.”
Because the exhaust is so...
Because the exhaust is so rolled over on the heads, the beefy Manton pushrods actually travel through holes that are machined in the block. This precludes bolting a set of Hemi heads on a “normal” non-Hemi big-block.
Corey worked with the experts at COMP Cams to build a solid-roller camshaft that would accomplish his goals of building good cylinder pressure without wasting effort and energy. They ended up with a grind that not only made killer peak horsepower but also had a big fat torque curve that would spin the Earth. The cam they installed was the second one they tested. “We set it in straight up and played with the lash adjustment a little bit just to find out what the motor was liking.”
None of that power would be possible, however, without the assistance of the monster CNC-ported heads from Indy Cylinder Head. Indy has been in the Hemi business for over 35 years and has amassed a volume of knowledge about the subject second only to Mopar itself. Corey says, “There really hasn’t been a whole lot of development on the Hemi for quite some time until Indy Cylinder Head got into the game.” The 514-cube engine in question needed a cylinder head that was capable of flowing a large mass of air in order to meet the targeted 800-plus horsepower, but was not going to be so large that low-rpm air velocity and torque would suffer from sluggish ports. The answer came in the form of Indy’s 426-1RA Legend heads. Corey’s “RA” heads have spacious 295cc runners. “They flowed about 483 on the intake and 330 on the exhaust at .700 lift. They have a raised exhaust, which certainly helps out on the flow. When I bought them, I had them retain the stock Hemi valve sizes, which were a 2.25 intake and a 1.94 exhaust, and I did that just to get a little more velocity out of them for more torque. It’s hard to get a Hemi to give you torque down low.”