There’s just something about a Southern man. There’s a modest nonchalance and reluctance to boast about his accomplishments that disarms you just before you realize that this good ol’ boy knows what he’s doing. Robert McDonald is that typical Southern man. Residing in the heartland of racing just outside Hickory, North Carolina, Bullet Bob and his friends at Atlantic Engines have been building high-performance gas and diesel engines for racers both local and nationwide. The kind of racers who would stop to help you fix your car for the race, put you in the wall to win the race, and then help you afterward. It’s just the way things work there.
Bob’s latest creation was this mild, unassuming little late-model Gen III Hemi that would look perfectly at home in a Charger or Ram pickup. Thing is, just like the Southern gent, the little engine is not all what it appears to be.
Talking with Thor from Moroso,...
Talking with Thor from Moroso, Atlantic’s Bob McDonald discovered their slippery black billet valve covers for the engine. He added a breather to each side since there was no PCV system on the engine.
Their engine started out life as a stock 5.7 belonging to a Yankee way north of the Mason-Dixon line. Salt and corrosion pitted away at the exterior cast iron while internal neglect put the engine in an overheating situation and lead to its ultimate demise. Bob bought the core and set about resurrecting the phoenix. With limited experience in building late-model Hemis, he had goals of learning the intricacies of the engine while building something that made tons of power, was reliable, fuel injected, and didn’t break the bank. Oh yeah, it was supposed to be going in an early Barracuda so you know it had to look good too.
When asked about his initial experience with the Hemi, he laughed and said: “I had no idea what I was getting into. I’d worked on a few but I had no idea. This won’t fit this because it’s a different year model and so on, but I said we’ll do it. The biggest problem I ran into was finding someone to machine the Hemi. It is a very unique engine.” In fact, even though the engines first came out in 2003, very few have passed through the doors of performance engine shops and even fewer still ended up as actual high-performance engines. Unlike the proliferation of GM LS and Ford Mod motors, it seems that most hot rodders have shied away from the late-model Hemi. Sure, most of the cars that the Hemi comes in are a little portly, but since designers at Mopar had the sense to make the bellhousing pattern identical to that of the early small-blocks, there is really no reason not to drop one in a lightweight muscle car–era A- or B-body for fun.
The ceramic-coated Hedman...
The ceramic-coated Hedman headers already came with an oxygen bung welded in place. A good old-fashioned set of glasspacks knocked the exhaust note to a tone where it was only mildly painful. Bob says he was actually surprised at how tame the engine ran at idle, and the dyno operator claims he’d never heard one so smooth under full load at 2,500 rpm.
Prior to machining the block, Bob gave it a half-fill of Hard Block to be sure the semi-open deck cylinders didn’t move around too much under load. Once cured, the block was punched to an even 4-inch bore to give the heads room to breathe and add some cubes.
Decking the block is tricky, since it is super wide and can be a pain to set up in most surfacing machines. Fortunately, Bob hooked up with engine machinist Mike Ege, who performed the block work with as much care as he would on one of his top NASCAR engines.
For those looking to build a similar combo, the 6.1 block can be used as it comes from the factory with a 4.055-inch bore, but expect to pay extra for the core as it is a rarer entity that sports a factory forged crank, stronger rods, and piston oilers—perfect for forced-induction guys who don’t want to buy a whole rotating assembly. Another difference between the 5.7 and 6.1 is a revised water passage design. Bolting a set of 6.1 heads on a 5.7 block has been done, but Bob pointed out that due to the water passage differences between the blocks, care has to be taken to be sure there will not be a water leak from the mismatch.
Looking to stroke the engine to its final 407 ci, different crankshafts were considered. Mopar Performance and Scat both offer 3.795-inch stroke forged cranks, but ultimately the Atlantic Engines crew decided on using a Callies Compstar crank sporting a massive 4.050-inch stroke that was still able to use nice long 6.125-inch Callies rods. A side benefit of the Callies crank is that if it is installed in a standard-bore 5.7, it ends up at 392 cubes, and in a 6.1 block, it puts out a magical 426 ci. Serendipitous coincidences hailing back to the Hemi’s history!
Running the engine with a...
Running the engine with a throttle cable instead of drive-by-wire required the use of an aftermarket throttle body. The bolt pattern on the throttle body and the intake didn’t match, so Atlantic fabbed up a 1.25-inch adapter plate to make it work out. They were able to use the FAST IAC, which is more or less a modified GM unit, to get the idle speed right.
A shortcoming of the Hemi-type...
A shortcoming of the Hemi-type combustion chamber lies in its inherent poor emissions capabilities. During overlap, since the intake valve and runner is basically pointing right at the exhaust valve, it ends up dumping a good portion of unburned fuel directly out of the exhaust. Chrysler had a tough time actually making the engine pass emissions guidelines to make it legal. Running dual spark plugs, as blown Alcohol and Top Fuel guys have known for years, allows the tuner to stagger the timing of each plug. He can initially light the fire, then bring in the second plug to really help it or in case the flame was blown out. The second plug can also add a great deal of spark dwell to the burn time, picking up a little power and knocking down a little more on emissions.
Like the old-school Hemis,...
Like the old-school Hemis, the exhaust pushrods run through the head to the back side to activate the exhaust rockers. Obviously the valvetrain is non-adjustable, which limits the amount of lift the heads are capable of without compromising geometry. It also eliminates any chance of a solid-lifter cam.