The year was 1955. President Eisenhower resided in the White House, Rosa Parks refused to sit at the rear of the bus, and the Brooklyn Dodgers defeated the New York Yankees in the World Series. The year 1955 also marked the introduction of the Chevrolet small-block engine. It measured 265 cubic inches and soon made the division's passenger cars the ones to beat at the track. Over time the small-block reached 400 ci, and it is still being produced in GM's Toluca, Mexico, plant for over-the-counter replacement purposes.
Pictured here is the deck...
Pictured here is the deck surface of the SB2 cylinder head (pictured here), and the R07 cylinder head (below).
As the 1998 NASCAR Winston Cup season began, it was decided that the Gen-1 (SB1) Chevy engine had reached its limits. With parts having a short lifespan, and no significant gains in power, Team Chevy gained approval to begin use of the newly designed SB2 (small-block 2). While the bottom half was very similar to the SB1, the cylinder head design changed drastically. The port layout, valve angle and combustion chamber design were all new. The SB2 would help level the playing field against other manufacturers. The SB1 made decent power, but needed more torque down low to get off the corners faster. The SB2 provided this additional gain in torque, and this engine was used in Nextel Cup Racing until this year.
Notice the more consistent,...
Notice the more consistent, uniform design of the plug angles, valve seat configuration, and port spacing of the R07 cylinder head. The R07 also contains a more prominent deck surface.
As early as 1999, GM began working on a successor to the SB2 engine. During the 2004 Cup season, NASCAR began holding discussions with key automotive manufacturers about a possible "Engine of the Future," which would coincide with its "Car of Tomorrow" program. While the Engine of the Future talks fizzled away during 2005, they did establish a base for future engine design in NASCAR. Eventually, Nextel Cup Series Director John Darby developed a list of parameters to define the envelope for all manufacturers. Jim Covey, NASCAR engine program manager for GM Racing stated, "We had already started to lay the foundation for a future Chevrolet engine, and we were able to adapt that design to the Chevrolet R07."
Once the program was given the green light, the R07 development team (consisting of Ed Keating and Ron Sperry, who were in charge of cylinder heads and intake manifolds, and Ondrej Tomek, who was responsible for the cylinder block) worked closely with key Chevrolet teams. GM Powertrain and its suppliers had the prototype R07 engine running durability tests on a dyno six months beyond their start date. The main reasons for production of this engine were to produce competitive power, reliability, and improved safety and to reduce costs for Chevy teams.
From the exhaust flange side...
From the exhaust flange side of the cylinder head, you can see the mirror port design of the SB2 (below), as opposed to the alternating port design on the R07. The new design facilitates better flow and added heat dissipation.
The R07 made its debut at the Samsung 500 at Texas Motor Speedway this past April. In May, Kevin Harvick made Chevrolet history by scoring the first win for the R07 engine at the Nextel All-Star Challenge at Lowe's Motor Speedway in Charlotte, North Carolina.
Technical Aspects
The R07 maintains the traditional two-valve/pushrod design as it has been since 1955. The R07 displaces a maximum of 358 ci with a maximum cylinder bore diameter of 4.185 inches. The cylinder block is iron cast with internal oil and coolant passages, eliminating the need for most exterior lines (as were run on the SB2). In order to improve coolant circulation, and lessen temperatures at critical locations, the R07 has a bore distance of 4.5 inches (as opposed to the 4.4 inches in the SB2).
You may be asking yourself...
You may be asking yourself why the ports are so small. These are the as-cast heads from GM. Each team spends numerous hours researching and developing special porting techniques to maximize flow numbers (within the rules of course). Porting must be done in a spherical manner; teams may not change the positioning of the port (higher or lower).
The R07 block design uses a six-bolt head bolt pattern as opposed to the traditional five-bolt pattern. This improves head gasket sealing, along with reducing cylinder bore distortion.
The R07's camshaft resides higher in the block than the SB2's, thus allowing for a shorter/stiffer pushrod to be used. This dramatically improves valvetrain geometry at high rpm. The raised camshaft allows room for inboard piston squirters, which spray the underside of the pistons for additional cooling. The camshaft is also isolated from the crankcase in order to lessen windage from oil falling onto the crankshaft, in essence robbing power.
The R07 cylinder heads resemble the LS-series production cylinder heads, which contain alternating exhaust and intake valve configuration (as opposed to the SB2's "mirror port" design). The shallow valve angle provides a more efficient combustion chamber design, which also allows the engine builder some room when achieving the NASCAR-mandated compression ratio of 12:1. The SB2 contained a 12 degree intake valve angle, coupled with an 8 degree exhaust valve angle-the new R07 uses an 11.5 degree intake valve angle with a 7.5 degree exhaust valve angle.