Inside The G3 Hemi Cylinder Head

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Is it a real Hemi? That was the cry nearly 10 years ago when the daring engineers at Chrysler slapped the sacred slur on the valve covers of their new V8 engine and unceremoniously dropped it into a truck. The trolls on the Web were so busy complaining that they overlooked what has to be the best mass-production cylinder head Mother has ever produced. Now, after corporate bloodbaths, government meddling, and bratwurst in the company cafeteria, the Hemi is really getting good. Especially the heads. Let’s take a look.

As this is written, there are four cylinder head designs. In 2003, the 345-inch 5.7 Hemi received the first, followed in 2005 by the 6.1L design. After 2009, the 5.7L Eagle and 6.4L Apache head appeared along with Variable Valve Timing (VVT) and the larger 392-inch engine. As the engines got larger, the heads improved with the help of larger valve sizes and improved ports. As cams got bigger, the beehive springs got more aggressive and capable of handling more lift. The current king is the Apache head that is reported to flow more than 340 cfm.

We’ve been playing with the heads on the eBay 5.7L Hemi that we are currently plumbing into the ’71 Demon project car. Car Craft fabricator Grant Petersen and Jimmy White from Circle City Hot Rods created the headers for the turbos using 5.7L flanges from Stainless Works. During this process we began bench-racing upgrades for more power and quickly realized we had the smallest heads available. Of course, we wanted more so we called Dave Weber at Modern Muscle Performance to see what would fit and how far we could go.

5.7L Hemi 2003–2008

Ccrp 1210 Inside The G3 Hemi Cylinder Head 02

The new Hemi head is made from aluminum and is not interchangeable left to right on the engine. It has four head bolts per cylinder and a shaft rocker system.

The new Hemi head is made from aluminum and is not interchangeable left to right on the en

The 5.7L cylinder head can be found on Dodge trucks and non-SRT passenger cars, making it the most common head in the family. It has a 161cc intake port that flows between 250-280 cfm at 0.600 lift, depending on the flow bench. We’ve seen published numbers stating 265 cfm, and we’ve independently tested the stock pair off the ’06 eBay Hemi from a Dodge Ram truck and saw 259 cfm. The intake valve is 2.00 inches and range from 4.850–4.900 inches in length.

The exhaust port is a small square with a 50cc port volume and flows around 180 cfm at 0.600 lift. Again, using independent testing, we saw 160 cfm through the port. The valve measures 1.55 inches in diameter and, like the intake valve, is roughly 4.850 inches long and has a solid stem.

All new Hemis use twin plugs that fire twice once BTDC and once ATDC on the power stroke to reduce emissions by burning unused hydrocarbons. The 5.7 head features an 85cc open combustion chamber.
All new Hemis use twin plugs that fire twice once BTDC and once ATDC on the power stroke t
The non-Eagle 5.7L head is the only one with a square exhaust port. The 5⁄16 steel exhaust valve is 1.55 inches in diameter, and the rocker arm has a 1.65:1 ratio.
The non-Eagle 5.7L head is the only one with a square exhaust port. The 5⁄16 steel exhaust
The intake port is a large rectangle and has a 1.65:1 rocker ratio and a 2.00-inch valve. The notch at the top of the port is for the fuel injector.
The intake port is a large rectangle and has a 1.65:1 rocker ratio and a 2.00-inch valve.

In this cross section, you can see the bullet-shaped tube for the spark plug and the intake (right) and exhaust (left). Behind the roof of the exhaust port is water, so be careful when porting in this area. Ask us how we know. The 18.0-degree intake and 16.5-degree valve angles help to unshroud the valves on the then-small 3.92-inch bore on the 5.7 engine.
In this cross section, you can see the bullet-shaped tube for the spark plug and the intak

5.7L Flow Chart*

Lift	Intake CFM**	Exhaust CFM**	I/E Percentage
0.100	71	38	54
0.200	168	109	65
0.300	239	163	68
0.400	270	180	67
0.500	284	183	64
0.600	285	185	65
0.650	285	186	65

*Flow testing performed by Dave Weber at Modern Muscle Performance using a 4.060 bore plate, no exhaust flow pipe on a Superflow 1020 flow bench at 28 inches test depression.

**Rounded to the nearest decimal

5.7L Eagle 2009–Present

Ccrp 1210 Inside The G3 Hemi Cylinder Head 08

The square-shaped 190cc intake port flows like a crazy aftermarket head. It flows 331 at 0.600 lift.

The square-shaped 190cc intake port flows like a crazy aftermarket head. It flows 331 at 0

The Eagle head arrived in 2009 with VVT on non-SRT Dodge passenger cars and trucks. As with the early head, the Eagle uses rocker shafts and 1.65:1 ratio rockers, but there are big differences in the size and shape of the intake port and the rest of the valvetrain. The Eagle uses 2.05-inch intake and 1.55-inch exhaust valves that are not only larger, they are also longer than standard. The rocker support is taller, and the valve-guide support boss sits higher on the top side of the head, moving it out of the intake port. The Eagle uses a larger square port like the 6.1L that flows a massive 331 cfm right out of the box.

The D-shaped 60cc exhaust port on the 5.7L Eagle head flows 181 cfm at 0.600 lift.
The 5.7L Eagle head uses a closed 65cc combustion chamber.
A quick way to spot a set of Eagle heads is the notched valve cover rail. The early 5.7L and 6.1L valve covers can’t be bolted to the later heads.
A quick way to spot a set of Eagle heads is the notched valve cover rail. The early 5.7L a

5.7L Eagle Flow Chart*

Lift	Intake CFM**	Exhaust CFM**	I/E Percentage
0.100	82	45	55
0.200	175	110	63
0.300	243	160	66
0.400	300	180	60
0.500	323	181	56
0.600	331	183	55
0.650	331	186	56

*Flow testing performed by Dave Weber at Modern Muscle Performance using a 4.060 bore plate, no exhaust flow pipe on a Superflow 1020 flow bench at 28 inches test depression.

**Rounded to the nearest decimal

6.1L 2005–2011

Ccrp 1210 Inside The G3 Hemi Cylinder Head 11

The 6.1L intake port is different from the 5.7L, so you will need the intake from a 6.1L or Eagle for a head swap. The angle of the valves makes it possible even with the small 3.90-inch bore.

The 6.1L intake port is different from the 5.7L, so you will need the intake from a 6.1L o

This head is found only on SRT-8–equipped passenger cars and trucks. It uses a square intake port that measures around 188cc* and flows 321 cfm at 0.600 lift using a 2.08-inch valve. The D-shaped 57cc exhaust port flows 194 cfm at 0.600 lift using a 1.650-inch exhaust valve. The cam is larger than the 5.7L version, making the beehive spring good enough to handle up to 0.580 lift. At 74cc, the open chamber is smaller than that on the 5.7L yet larger than that on the Eagle, making it a good head for a big-bore 5.7 swap (see the Step Up sidebar). Aside from the larger- diameter valves, the valvetrain uses the same 1.65 ratio shaft rocker system and valve locations as the 5.7L Eagle head.

*Based on in-house measurements at Modern Muscle Performance.

6.1L Flow Chart*

Lift	Intake CFM**	Exhaust CFM**	I/E Percentage
0.100	81	39	48
0.200	176	129	73
0.300	243	184	76
0.400	290	192	66
0.500	312	192	60
0.600	321	194	60
0.650	322	195	61

Ccrp 1210 Inside The G3 Hemi Cylinder Head 12

The exhaust port has a D shape instead of the small 5.7L square.

*Flow testing performed by Dave Weber at Modern Muscle Performance using a 4.060 bore plate, no exhaust flow pipe on a Superflow 1020 flow bench at 28 inches test depression.

**Rounded to the nearest decimal

6.4L Apache 2011–Present

This is the latest head that you will find on ’11 SRT 6.4L Challengers, Chargers, and Jeeps, and it makes us giddy. It uses the same rockers and bolt pattern as the 6.1L but steps up to 2.14-inch intake and 1.650-inch exhaust valves. The square intake ports are closing in on 2x2 inches and the flow is in the 340 cfm range. To fit the larger valves and improved port, the guide is moved outside the port so the heads will only fit a 6.4L engine or something with 4.06-inch plus bore and custom pistons with the correct valve reliefs.

We can’t wait to play with a set of these. The 1.920x1.800-inch intake ports are nearly vertical to the cylinder. Reminds us of the 4V Cleveland head for its absurd size.
We can’t wait to play with a set of these. The 1.920x1.800-inch intake ports are nearly ve
The exhaust port is equally impressive. With all raised port heads, a dedicated intake and exhaust manifold is required to make it work.
The exhaust port is equally impressive. With all raised port heads, a dedicated intake and
The Apache uses a closed 74cc combustion chamber.

6.4L Apache Flow Chart*

Lift	Intake CFM**	Exhaust CFM**	I/E Percentage
0.200	178	128	72
0.300	248	183	74
0.400	312	211	68
0.500	335	228	68
0.600	339	237	70
0.650	340	240	71
0.700	339	241	71

*Flow testing performed by Dave Weber at Modern Muscle Performance using a 4.060 bore plate, no exhaust flow pipe on a Superflow 1020 flow bench at 28 inches test depression.

**Rounded to the nearest decimal

Step Up!

From left to right: 5.7L, 5.7L Eagle; 6.1L, 6.4L Apache.

For the budget guy who just wants to port the cylinder heads and change the cam, the 5.7L heads provide a small cross section and good port velocity. If you are modifying a late-model Charger or truck, Weber recommends these two mods and a good exhaust system with headers to pick up between 100 and 110 hp at the wheels.

Guys who want to try the 5.7L Eagle head will need to add a 0.075-inch head gasket to lower the compression to a reasonable 11.0:1. You will also need D-port headers, a 6.1L or Eagle intake, and the raised valve covers. With the right cam, this mod should get you up to 420 hp at the wheel from a stock 5.7L–equipped vehicle.

A better bet is to use the 6.1L head on the 5.7. You’ll need to use the thicker head gasket, the D-port headers, and the 6.1L intake (or can you use the Eagle intake). The heads will flow like the Eagle ports and you get the improved valvetrain as well.

If you are thinking about the Apache heads for your 6.1L the only way to use them is on a custom build with large enough valve reliefs, or buy a 6.4L Hemi. When this issue went to press, no one had cracked the VVT on the computer to get a 6.4L transplant to work. The Apache head won’t work on a 5.7L.