If you haven't kept your ear to the ground, you may not have heard that Chevrolet has been developing a new racing engine for the past few years. It was kept quiet as GM worked to create the successor to the SB2.2 for NASCAR's Nextel Cup Series.

The engine, known as the R07, has finally been approved by NASCAR for Cup competition and should start showing up in cars after Daytona. It may take a bit, but Chevrolet will almost certainly make this new technology available to any racer willing to pony up the cash for the components. Although designed primarily for Cup competition, the SB2.2 has found its way into many different racing classes, especially dirt Late Models. We even know a team that's racing a detuned SB2.2 in an IMCA-style Modified (you can get pretty good deals on used Cup parts if you know the right places to look), and we expect the R07 to be no different.

With that in mind, we wanted to give you an inside look at the new cylinder heads for this motor. These heads are a clean-sheet design and not an evolution of the SB2.2 cylinder heads. MBE Cylinder Heads and Manifolds performs a good deal of R&D work for several top Nextel Cup teams as well as building head/manifold combinations for many Saturday night racers. Owner Matt Bieneman agreed to give us an up-close look at these new heads. GM has only recently allowed race teams to have these heads, and MBE hadn't even seen the block at press time. We are still so early in the process that when this was written, NASCAR had yet to release its final templates so that engine builders can know where the ports must be located. Still, there is a lot to be revealed about Chevy's newest race casting.

The Cup guys have a limited bore size, but this is a big deal to engine builders with a more open rule book. The R07 engine is designed with a 4.500-inch bore spacing compared to the SB2.2's 4.400 spacing. This means the opportunity for not only bigger cylinder bores, but also better cooling between the cylinders. The wider bore spacing also means there is more room for bigger valves. Bieneman says that along with the relocated bore centers, the valveguides have also been separated a bit more. He has found he can stuff a 2.225 intake and 1.600 exhaust valve in each of the combustion chambers, while the maximum valve sizes in the SB2.2 were 2.180 and 1.600, respectively. The wider bore spacing also means that when the valveguides are separated by that extra margin, shrouding shouldn't become a problem.

One of the hallmarks of the Chevy small-block has always been the valve arrangement. It places an exhaust valve at the edge of the head, followed by two intakes, two exhausts, two intakes, and the final exhaust valve (E, I, I, E, E, I, I, E). The benefit of this arrangement is that it places all four intake valves as close to the center of the head as possible and equalizes the intake port lengths. The SB2 is slightly different, with a valve formation that puts the intakes on the outside edges (I, E, I, E, E, I, E, I). Both systems, however, also place the two center exhaust ports side-by-side, which is a notorious hot spot in almost all Chevy performance engines. The heat can be such a problem that many engine builders say that it causes additional bore distortion in the two center bores.