Chevrolet's newest racing engine, the R07, is still in the very early stages of developmen
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 R07 head (left) is a rare casting, hence the smaller-looking intake ports. The SB2.2 (
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.
The new valve arrangement of the R07 head separates every exhaust valve by placing them be
We laid ink pens along the line between the center of the intake port opening and the cent
This is a big-block drag race head, but it is a good example of a "twisted" port that may
Another comparison shot between an R07 (left) and an SB2.2. It is difficult to see with th
The new heads remove this situation by rearranging the valve order. Now, it is I, E, I, E, I, E, I, E, and each exhaust valve is surrounded by an intake to help cool it. The new valve arrangement will, however, require a different lobe arrangement on the cams. Of course, it is already a given that the SB2.2 and other Chevy small-block cams will not interchange with the R07 because of the wider bore spacing.
In addition, removing the hot spot between the exhaust valves will help equalize the coolant temperature within the block, which will reduce localized movement of the material. This means better ring sealing and possibly even better sealing at the head gasket. The cool air flowing through the nearby intake ports will also help make the environment a little friendlier for the exhaust valves and seats.
In addition to the new valve arrangement, there has also been a significant change made to the ports. Almost all small-blocks from any manufacturer use a port angle of at least 10 degrees. This angle sends the air/fuel mixture through the port and into the combustion chamber on an angle so that it creates a vortex, or swirl, inside the chamber. This swirl helps keep the fuel suspended in the air so that it burns as efficiently as possible when the spark plug fires.
This new port, however, is very straight and very short. Veteran cylinder head porter Dennis Warner calls this a "low-swirl port" but believes the overall improvements in flow should outweigh the disadvantage that comes with less swirl. One trick he feels might work to increase swirl is to "twist" the port so that the walls, while still parallel, are no longer vertical. This will help produce more tumble and swirl before the air/fuel charge enters the combustion chamber.
This hole is an oil gallery that will feed oil from the block to integrated valvespring oi
As this feature went to press, Bieneman and Warner said that they had little information on how well the ports will actually flow because NASCAR had yet to release the templates they must work within, and actual castings are still so scarce that they cannot afford to experiment until they know the exact rules package.
Along with the straighter ports, the valve locations have also been moved closer to the side of the head. The result is that the valves are more staggered than before. This should help the rockers be more centered over the appropriate cam lobe and straighten the pushrods. Bieneman says that this change will allow the wider ports to deliver even better flow numbers.
Since the intake ports are so straight, both Bieneman and Warner believe that the intake manifold design that will work best with these heads will have a very large plenum that is extended toward both the front and back of the engine. This large plenum will help move the outside intake runners closer to the ports so that they won't have to curve as much to make the port entrance. This design will also shorten the outside runner length to help it match the length of the interior intake runners.
Of course, this short-runner/big-plenum design lends itself well to Cup racing, where the rpm is high and the power range is narrow. In a short-track car-say a dirt Late Model-the plenum can easily be decreased or even raised to increase the runner length and move the powerband lower in the rpm range. Another difficulty with a large-plenum manifold is that it reduces the signal at the carburetor. Warner says that this can be overcome, but it requires a crafty carburetor tuner.
This manifold is for an SB2.2, but the design is a good example of what Bieneman and Warne
The raised outer rail on the head is almost certainly designed to catch oil and hold it ag
Below each of the intake ports is an inlet to bring water from the valley cover to the cyl
The R07 has noticeably more material on the top of the head. This adds approximately 5 pou
Anyone familiar with race engines will quickly notice that the head-stud holes on the new Chevy head have been moved away from the combustion chambers. Some might even call it a "Ford-style" stud arrangement. This will definitely be a benefit, as the old stud location was so close to the cylinder bore and combustion chamber that it could cause distortion. Although we haven't seen the block, it is a good guess that the area that the head studs or bolts thread into in the block will be completely separate from the cylinder bores. This will not only ease distortion-inducing stress on the bores, but also create more room for the water jackets to provide coolant across more of the bores' area.
Since the SB2.2 was introduced in the late '90s, many teams have begun flooding the valve covers with oil to help keep the valvesprings cooler. Some say keeping the springs surrounded by oil also helps dampen damaging harmonics. To aid this, the outer rail on the R07 head has been significantly raised. If you pull your valve covers a few minutes after a run, the raised rails will catch the remaining oil and you won't drench yourself. Additionally, the oil drain-back holes are easily accessible to change out the oil restrictors for different sizes, which will aid tuning.
It appears that Chevrolet's engineers have also made another change to help racers when it comes to oil control. At the lower corners of the heads are galleries that lead from the block to the top of the head at the inside edge of the flange for the valve cover. There is even a groove for an O-ring at the topside of this gallery. It appears this will feed pressurized oil to the valve cover, which will have integrated valvespring oilers. Integrated oilers won't necessarily improve performance over existing systems, but it will eliminate exterior plumbing and simplify the system.
This hole is an oil gallery that will feed oil from the block to integrated valvespring oi
Finally, the R07 engine will use a valley cover that is separate from the manifold, like the SB2.2. Also, the valley cover will be wet and provide water to the cylinder heads. But unlike the SB2.2, the R07 includes separate water inlets into the head for each chamber. The SB2.2 only had inlets at the corner of the heads, which made it difficult for engine builders to get cool water to the interior exhaust valves. As a result, many were forced to plumb exterior coolant lines directly from the water pump to inject cool water into the water jacket between the two interior exhaust valves. Between the relocation of the valves and the four water passages into the cylinder head water jacket, cooling should be much improved and the external plumbing for the coolant should no longer be necessary.
Here's a trick the Cup teams have been using for a few years that MBE has begun providing to other teams. Below is an example of a cylinder head for a Sprint Car, but it will work in many different applications. Owner Matt Bieneman has gotten rid of the valve seal by using an O-ring inside the valveguide. The advantage of this is that it allows the guide to be taller (equal to the height of the top of the old valve seal) without limiting valve lift. In this application, it equals approximately 0.150 more guide height, which helps stabilize the valve. Now Bieneman can use smaller valve stems, which cuts valvetrain weight, without sacrificing stability.