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2015 SRT Hellcat
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Discussion Starter · #1 · (Edited)
Cool, older article from Hot Rod magazine (originally published in 2012), so no breakdown of the Hellcat's SC'd 6.2 Hemi, but still an informative read! :smileup:

Is it a real Hemi? That was the cry nearly 10 years ago when the daring engineers at Chrysler slapped the sacred Hemi 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 Hemi 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 6.1 hemi design. After 2009, the 5.7 Hemi Eagle and 6.4 Hemi 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.

5.7 Hemi 2003–2008

The 5.7 hemi 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.

5.7L Eagle 2009–Present

The Eagle Hemi cylinder 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.

6.1 Hemi 2005–2011

The 6.1 Hemi 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 on the 6.1 Hemi 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 6.1 Hemi valvetrain uses the same 1.65 ratio shaft rocker system and valve locations as the 5.7L Eagle head.

6.4 Hemi Apache 2011–Present

This is the latest head that you will find on ’11 SRT 6.4 Hemi 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 6.4 Hemi engine or something with 4.06-inch plus bore and custom pistons with the correct valve reliefs.

Step Up!

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.

Slideshow of the different Hemi heads

Source (click this link to see the flow charts for the different Hemi engines. They didn't format correctly in this thread)

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