Cylinder Head Testing - LS2 Dyno Thrash Part II: Head Shootout

Earlier this year, we began a LS2 testing program at Dan Millen's Livernois Motorsports, one of our favorite Detroit area speed shops. In case you are just tuning in, the LS2 is the amazing, pushrod V-8 that comes standard in many hot GMs, like the base C6 Corvette, GTO, Trail Blazer SS, and Chevrolet SSR. Or, if you've got a project car in your garage that is just calling for one of the most potent all-American small-blocks ever built, the LS2 is available as a crate engine directly from GM Performance Parts. In stock form, the LS2 offers 400 horses and 400 lb-ft of torque from a 10.9:1 compression 6.0 liter displacement. But the LS2 has a ton of hidden potential from very minimal modifications. As an example, Livernois took our LS2 to the dyno, and we demonstrated how easy it is pick up 80-100 hp with a modest camshaft swap and ported stock heads.

To think that a 364-inch small-block that is already making 400 hp can pick up that much power for so little money really points to the advances that GM Powertrain has been making in developing and perfecting the LS family of engines. Part of the secret is the outstanding head design that promotes good low lift velocity and outstanding upper lift flow. With all of that going for it, it makes one wonder just how effective an aftermarket head can be. As we found out in this study, aftermarket heads can certainly add to the bottom line, but it also opens up more questions. Can more inches and a bigger camshaft make an aftermarket head even more valuable? That test will have to wait for another day, but in the mean time, read on and see what some of the best in the aftermarket head business have available for one of America's favorite small block V-8s.

The Test
The call went out to several of the top cylinder head manufacturing companies: "GM High-Tech Performance magazine is doing a head shootout on an LS2. Do you want in?" Some shops said no, some never returned our phone calls, but most companies wanted to get in the show. It actually took several months to get this story together. We had the engine and the shop, but a couple of the cylinder heads used in this study are tough to get. For example, the AFR units are extremely popular, and AFR brass had to go above and beyond--pulling a set of their heads from the production line--just to get us a sample. And the TFS LS2 heads tested here are quite clearly prototype units that no one but us had access to outside of the TFS testing labs. In the end, we had assembled four aftermarket heads, and as a courtesy to the shop that was going to be doing all of the labor and testing, we allowed Livernois to throw a set of its very trick, Stage III CNC-ported LS2 heads into the mix. Conflict of interest? No--it simply gives our readership an idea of what a good port shop can do with your stock heads, and then what that head will do for your engine combination. For the engine, we took our stock LS2 and outfitted it with one of the Livernois Stage II camshafts that had worked so well for us before. The Stage II Livernois camshaft specs out like this: 232/232 @ .050, .600 lift on a 114 lobe separation angle. We did this with the assumption that if an enthusiast is to the point where they are shopping for a set of good aftermarket heads, then they probably already have a cam or have their eye on one. The Livernois Stage II cam is a great choice for the serious LS2 street car while in most cases not requiring additional valve clearance, i.e. increasing valve reliefs in the piston face to accommodate the movement of the valves.

On the dyno, we took advantage of a set of Kook's 1.875-inch primary dyno headers. Not only does Kook's offer you the best materials in the business, but their stuff fits. There are a few header shops in the country that we consider to be producing "investment grade" headers, and Kook's is certainly in that club.

All tests were performed on the Livernois Superflow 901 water brake dynamometer, which is good to 2,000 ft-lbs. The Livernois Motorsports dyno cell is temperature controlled, and it was maintained at 68*-70* during each test. Our goal was to keep the air/fuel ratio as consistent as possible from 12.5-12.8 for all tests. Of special note, we did run the AFR head richer and leaner at the request of AFR. We did note some detonation when the engine was leaner, and the power numbers didn't change much either way, so we discarded those numbers. One word on our data interpretation: this is much more of a comparison than a shootout. It's impossible to declare a winner with any of these heads because their applications are endless. However, we are going to attempt to compare these heads so that you are well-informed consumer. After all, this is a great time to be an LS engine enthusiast, and the real winner is the thousands of enthusiasts putting these engines together. With that as background, let's see how the heads stack up.

We started our LS2 head testing with a trip to the Livernois flow bench. Not surprising for the amount of power that the LS2 is capable of generating, all of the heads flowed a lot of air. The AFR and TFS castings offered outstanding low lift flow numbers with solid top end flow, with the TFS head offering the best flow rate test (a super impressive 327 cfm at .600-inch lift.). The completely tricked out stock units were somewhere in the middle with surprisingly close numbers to the two more exotic AFR and TFS heads. And, the Edelbrock and Dart heads, designed for fit on the LS1 block (read: shrouded valves) were slightly lower at the top of the scale while offering impressive low-lift air flow characteristics. Still, any head that flows over 300 cfm and is going on a 364-inch short-block has the potential to make a ton of power.