S&S Cycle X-Wedge Engine - First Look

The common front and rear cylinders are die-cast aluminum and fitted with an aggressively textured cast-iron liner for improved retention and heat transfer. The cylinders are relatively short in length and secured using a five-bolt stud pattern. A five-bolt pattern offers higher and more even clamping forces than a four-bolt pattern, resulting in improved base and head gasket sealing. For improved cooling, the cylinders have about 15 percent greater fin area than an S&S Evo-124 cylinder and are round in shape with no top-end oil return galleys for reduced distortion. The current cylinder liner accepts bore sizes between 4.125-inch and 4.375-inch.

S&S engineers topped of the X-Wedge engine with aluminum cylinder heads and a wedge-style combustion chamber. In fact, the X-Wedge was named for the shape of its combustion chamber. Unlike earlier V-Twin engines, the X-Wedge chamber sets the valve stems parallel to one another instead of angled fore and aft. This design allows for a more compact chamber with higher compression ratios using a flattop piston. The wedge chamber also offers reduced surface-to-volume area for better heat retention, a centrally located spark plug for short flame travel, and generous squish area for high turbulence. The result is excellent cylinder filling and efficient, unimpeded combustion for optimized power along with reduced potential for detonation and fuel octane requirements. Using a flattop piston with the wedge chamber on a 117ci engine produces a 9.75:1 mechanical compression ratio.

Large-bore engines provide much room for large valves. As such, S&S engineers designed the X-Wedge head with a 2-inch intake valve and modern intake port. The exhaust side sports a 1.6-inch exhaust valve along with an efficient, short exhaust port to minimize heat loss and maximize exhaust gas velocity for optimum cylinder scavenging. A single beehive valve spring (progressively wound and tapered from bottom to top) per valve minimizes harmonics and allows for reduced valve-seat pressure.

In the rocker box area, the X-Wedge head offers improved rocker arm design. Rocker arms on earlier V-Twins are heavy, long, and tend to flex. The result is inaccurate valve control and reduced power. In contrast, the X-Wedge rockers are arranged transversely, which keeps valvetrain components in a single plane. The result is a lighter, stiffer valvetrain and more accurate valve action. X-Wedge rockers are automotive-style, stamped out of steel and tipped with rollers for reduced friction and wear. The 1.7:1-ratio rockers are set parallel to the valves and attached to head studs instead of the rocker cover as with earlier V-Twins. S&S engineers also wanted to eliminate the earlier multi-piece rocker covers, which provide poor rigidity for valvetrain support and often lead to oil leaks. X-Wedge rocker covers are one-piece and non-structural, requiring only one gasket surface to maintain, which offers a wide clamping area for solid gasket sealing.

Since the X-Wedge engine had to be worldwide emissions compliant, S&S developed a new closed-loop fuel-injection system using a new 52.3mm single-bore throttle body and port-mounted injectors controlled by a new proprietary electronic-management system. The new system includes one oxygen sensor for each cylinder, thereby processing each cylinder as a separate engine.

The X-Wedge engine represents a huge step forward for S&S. S&S goals were to design an engine with the look, feel, and smell of a traditional V-Twin, but with simplified engineering, superior durability, increased power, and compliance with worldwide emissions requirements. Clearly, the X-Wedge is elegantly simple while design improvements should eliminate earlier V-Twin durability gremlins. Rated at about one rear-wheel pound-feet of torque per cubic inch in emissions-legal trim, the X-Wedge provides an excellent foundation for even more performance. It seems to us that S&S is not only keeping it simple, but also maintaining the look, feel, and smell of the traditional V-Twin while meeting '08 and future worldwide emissions standards.

S&S X-Wedge
First Look Specs