Here's an article from Car Craft magazine that compares the various iterations of the modern Generation III Hemi Head. http://www.carcraft...._cylinder_head/ It gives good information on intake and exhaust valves along with flow charts for each. Below are some excerpts from the article. 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. *Based on in-house measurements at Modern Muscle Performance. 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. See the article for flow charts for each head. 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 valve train 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.