Gen III Hemi Engine - Southern Pride
Some good ol’ boys show us how to build a newfangled 640-horse pump-gas Hemi
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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.
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.
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!
Knowing that the Hemi comes with a 9.25-inch deck height, Bob subtracted the rod length and half of the stroke, leaving a 1.1-inch piston compression height that he related to Mahle, as they were contracted to manufacture the pistons for this build. Mahle coated the piston skirts with their Grafal coating and were able to reduce the piston-to-wall clearance, limiting piston rock and the wear, noise, and loss of compression associated with it.
All of the late-model Hemis came with hydraulic-roller camshafts, and Bob’s bullet was no different. Without the vast array of dyno data that would accompany something as mundane as a small-block Chevy, it took a bit of figuring to get a cam that would work the way he wanted it to. The requirements that Bob spec’d out were that the engine must make huge average torque and horsepower between 2,500 and 6,500 rpm, as the engine was to be used in the AMSOIL Engine Masters Challenge prior to its final destination in the ’Cuda. He spoke at length with Billy Godbold at COMP Cams who sent him a “small” and a “big” cam to try out. Like the older LA small-block engines, the Hemi uses a 57-degree lifter angle; however, they dropped the lifter diameter to .842 inch, like the GM camp. According to COMP, lifter angle and diameter, specifically the lifter roller wheel diameter, plays a huge role in determining the design of the cam lobes. Between those things and understanding how the Hemi heads flow compared to a typical Wedge head, the late Hemi cams are completely different than a “normal” cam. Additionally, the 2009-and-newer 5.7s employ Variable Camshaft Timing (VCT) that uses pressurized oil running to a unique camshaft sprocket, which can change the camshaft phase, advancing or retarding the cam as needed. Fortunately, Bob wasn’t saddled with that extra challenge when choosing a cam, since his was an earlier block. His final cam choice was cemented after speaking with cam guru Dema Elgin of Elgin Cams, who ground a COMP core to specs in between the “small” and “big” cams, which turned out to be the perfect choice.
When Bob was initially disassembling his engine and giving it the once-over, he did notice one more peculiar thing about the late Hemi: No oil galleys were feeding the lifters. Unlike most engines, the late Hemi feeds oil backward, from the top through the rockers, to the pushrods and finally to the lifters. Bob’s engine used the factory rocker arms for the engine, since at the time nothing in the aftermarket was available. “There’s nothing special about them, but there’s nobody making a set. Even at the PRI [Performance Racing Industry] Show you’re walking around and nobody’s making a set. You’re like ‘it’s been seven years guys and still nothing?’”
He had an “opportunity” for learning when freshening up the original rocker shafts. Since the heads were overheated originally, they were covered in scale, and being the fastidious engine builder that Bob is, he decided to pop out the freeze plugs in the ends of the rocker shafts to clean the inside. It turns out replacement plugs are not available, even from Chrysler. After much hemmin’ and hawin’, he just went down to the local dealer resigned to the fact that he’d have to buy new shafts to slide his nice, clean rockers on. Well, the shafts are only sold with rockers on them. (Head drops here.) On the plus side, a full set of brand-new rockers and shafts was only $140 a head. For both heads it was only $280! “Another lesson learned about the Hemi,” Bob says.
The perfect cam he now had was significantly dependant on the cylinder heads bolted on top of the block. To get the most out of the combination, Bob went straight to the horse’s mouth. He contacted Bryan Maloney of Maloney Competition Systems in Martinsville, Virginia, who was one of the original developers of the current 6.1 Hemi head and had a serious pedigree in the racing community. Maloney ended up porting the heads and intake to take full advantage of the big Ferrea 2.05/1.55 valves. On Bob’s flow bench, he says that while peak flow numbers aren’t everything, they do perform quite well, drawing in over 300 cfm by a scant .300-inch valve lift. That is one haulin’ port.
With a removable floor plate, a 6.1L intake manifold and plenum were ported by Maloney as well. Doing his best to make sure the port entries leading into each runner were even ensured that the air distribution among all eight cylinders was matched. Unlike a carburetor, which distributes fuel to each runner proportionally to the amount of air that the runner ingests, an EFI manifold will typically send the exact same amount of fuel to each cylinder regardless of the airflow in the various ports. That is just one of those little things that an experienced head and intake porter will attend to with the knowledge that if there is a cylinder that is typically lean or rich with a stock manifold, it can be fixed with the right porting.
To control the fuel, Atlantic Engines leaned on their friends from FAST and procured one of their FAST XFI 2.0 fuel injection systems. The new XFI 2.0 system is a logical progression of the original XFI unit. FAST took everything that racers and enthusiasts liked about the original XFI and added to it. Things like boost control features, wet and dry nitrous control, solenoid pulse frequency, and targeted air/fuel ratios for power adders make life mucho easier for making big power safely. They’ve also expanded their internal data logging controls to feature external arming. You know, for that guy who flips a switch at the back of your bumper before you launch. Intelligent Traction Control has also been upgraded to avoid erroneous starting line data. Naturally, it has a self-learn feature that Bob used to generate a working fuel map once the engine was up and running off the base map. One of the features that really stands out about XFI 2.0 is the fact that you don’t have to throw away your old XFI system to use the new features; they offer a firmware upgrade for a reasonable price that will bring your old system up to date. Also, their PN 301013 kit is a simple plug-and-play for the late-model Hemi crate or transplant engine using all of the factory sensors, which certainly made Bob’s life much easier.
Plain old pump gas was fed to the engine, and they didn’t do anything special for the squirters. “Those are just stock injectors out of a ’94 turbo Neon, and we got the fuel rails from Aeromotive.” Since the engine normally uses a drive-by-wire throttle blade, they chose to install a FAST 92mm throttle body that they adapted to the stock intake manifold via a custom spacer they built. With their friend Aaron at the laptop, tuning the XFI was as sweet as chess pie.
Bob’s learning curve was up and down throughout the process, and in one of the down parts, he found out that though the bellhousing was an easy match, finding a flywheel was not. “I had to get a steel flywheel for a late Hemi. Now you go to Hays or anybody else and they say ‘we don’t have that flywheel, sorry.’ So I go to Chrysler and say I need to order a high-performance flywheel. It comes in and I open the box and it says Hays.”
Exhaust for the Hemi-powered cars and trucks has come around as well. “The headers I had were just off-the-shelf Hedmans. I had flanges to build a new set, but didn’t really have the time. I wanted to do a set with equal length, one unequal length, a tri-Y, and do a lot of playing, but these turned out great.”
A Moroso road-race pan with the side wings cut back was chosen to hold six quarts of AMSOIL 15W-50 oil for the engine. Bob emphasized the importance of choosing the right viscosity oil for the engine. He’s found in testing with hydraulic lifter engines that using a traditional lightweight racing oil in a hydraulic lifter engine can cost an easy 5-10 hp by allowing the oil to bypass the lifter plunger, killing valve lift and duration. By using a Melling M-Select oil pump and the relatively thick oil, he was able to capture some of that lost power. A caveat to the thicker oil treatment is that if you are picking an oil for an engine that uses a displacement-on-demand or variable valve timing system, absolutely stick with the vehicle manufacturer’s recommendation.
Once the Hemi was complete, the boys stuck it on the dyno. True to form, the old feller running the dyno wore a set of coveralls, Carolina red clay-colored shoes, and had a drawl that belied the knowledge and experience that came from years of testing high-performance engines. Though skeptical at first, his eyes lit up a bit as the torque needle climbed and when the horsepower peaked at 644, he finally admitted: “You boys got yourselves a player.”
Atlantic Engines 407ci Gen III Hemi
Displacement: 407 actual cubic inches
Compression ratio: 11.2:1
Camshaft: Elgin hydraulic roller
Cam duration: 238/241 degrees at .050-inch tappet rise
Valve lift: .598/.598-inch
Rocker ratio: OEM 1.65 ratio
Top ring: .043 inch
Second ring: .043 inch
Oil ring: 3mm
Piston: Mahle dished
Block: OEM 5.7
Crankshaft: Callies Compstar
Rods: Callies Compstar H-beam
Cylinder head: OEM 5.7
Intake valve diameter: 2.05-inch
Exhaust valve diameter: 1.55-inch
Intake manifold: OEM 6.1
Fuel Injection: FAST XFI
Ignition: FAST XIM
407ci Gen III Hemi
RPM TQ HP
2,600 415 205
2,700 413 212
2,800 416 222
2,900 426 235
3,000 431 246
3,100 440 260
3,200 454 277
3,300 474 298
3,400 486 315
3,500 494 329
3,600 501 344
3,700 508 358
3,800 508 367
3,900 509 378
4,000 518 394
4,100 521 407
4,200 527 422
4,300 538 441
4,400 548 459
4,500 554 475
4,600 561 491
4,700 564 504
4,800 563 515
4,900 558 521
5,000 552 526
5,100 557 541
5,200 563 557
5,300 563 569
5,400 567 583
5,500 571 597
5,600 569 607
5,700 567 615
5,800 563 622
5,900 558 627
6,000 553 632
6,100 547 635
6,200 539 637
6,300 534 640
6,400 528 643
6,500 520 644
That's a nice HEMI !