Gen III Hemi Engine - Southern Pride

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.

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.

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!

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.

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.

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.

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.”

By the Numbers

Atlantic Engines 407ci Gen III Hemi

Bore: 4.000-inch
Stroke: 4.050-inch
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
Header: Hedman
Ignition: FAST XIM
Damper: ATI

Dyno Data

407ci Gen III Hemi