In one bay door goes the raw material: sheets of stainless steel, aluminum extrusions and castings, tubes of carbon fiber, and of course miles (and miles) of titanium and stainless steel tubing. Out another bay door flows a steady stream of finished product: exhaust systems some would call art more than performance accessories. Inside the 56,000-square-foot facility, artisans-- both human and machine--ply their craft: cutting, machining, stamping, bending and welding the raw material into its finished form. Follow along as we tour Yoshimura R&D's new Chino, California, production facility shortly after its completion to find out just how exhaust systems are made.
While most of Yoshimura's exhaust systems are delivered to your door almost completely assembled, there are a surprising number of component parts that need to be manufactured. Aside from springs, raw castings and carbon muffler sleeves, all the individual parts are fabricated in-house. Header tubing must be bent into shape and welded together. Spigots and flanges are stamped or machined. Canister end caps are manufactured using a variety of methods, depending on the shape and material required. Inner silencer cores are rolled and welded together, as are the metal outer skins. And finally, all the component parts are assembled. During the entire process, constant inspections for quality are made, as are between 20 and 30 checks for fitment. It's a complex process with an incredible number of detailed operations.
An overview of the production floor. Twenty welding stations are utilized for header and end-cap assembly. | 
A variety of punches, cutters, flange tools and benders perform the dizzying number of small operations required. Not seen here are the two rows of CNC milling machines used for fabricating end caps and other billet Yoshimura products, such as triple clamps and rearsets. | 
Four Eagle CNC tube benders are used to automatically form the header sections. In some cases, for an exact fit the tubes must be cut to length after bending, as even this machine is not quite accurate enough for Yoshimuras' requirements. |
Pre-bent header tubes. | 
The individual header parts are pre-assembled in a jig and welded by hand. There are 20 welding stations in total, with MIG welders for stainless steel systems and TIG welders for titanium. Some automation is incorporated, as preliminary welds are made with a rotating jig. A special process prevents contamination of the titanium welds. TIG welding is such an art that there are just four employees entrusted with that task. Yoshimura is the 12th largest buyer of titanium tubing in the world. |  |
For slip-fit joints, this mandril expands the end of a length of tubing. | 
Metal canisters are rolled from sheet stock on a CNC roller, then seam-welded in a CNC welding machine. Carbon-fiber wraps are one of just three items (the other two being springs and castings) not fabricated from raw stock in-house. | 
The huge number of canister styles available further complicates the production process. Yoshimura offers oval, round and tri-oval designs with stainless steel, aluminum, carbon-fiber and titanium wraps. The canister in the center is for Honda's CBR600RR--underseat exhausts add yet another dimension for pipe manufac- turers. Every muffler has a two-layer baffle with stainless steel inside fiberglass. This provides sufficient noise reduction while extending the life of the packing material. |
Aluminum end caps start as a huge extrusion or castings. | 
Castings | 
Offroad tri-oval end caps in midproduction. |
A one-hit punch machine stamps out stainless steel end caps from a gigantic roll of sheet stock. A similar machine spits out muffler clamps, which are then rolled and pressed into shape. Each canister style and material requires a different clamp design, as each has different expansion characteristics. | 
An army of CNC milling machines with multiple tool stations churn out aluminum end caps eight at a time. In a typical machine shown here, one jig of eight parts is being machined while a second jig is loaded. In two operations (one for each side of the cap) a part goes from raw stock to almost finished. A similar, five-axis milling machine is also used to fabricate the company's line of triple clamps (magnesium for the race team) and port four-stroke motocross cylinder heads. | 
A six-axis laser cutter makes stainless steel brackets and spigot flanges. The CNC machine can cut material up to one-half-inch thick. While the majority of header flanges fabricated by Yoshimura are stainless steel, the pipes used by the race team have--you guessed it--machined titanium bits. |
Exhaust R&D
Now we know the how behind exhaust pipe manufacture, but not the why--as in why the individual tubes and parts have the size and shape they do. For all the automation and advanced technology on the manufacturing side, exhaust-pipe design is still mostly a trial-and-error process, and in fact the design team at Yoshimura is largely based on the experience of CFO Mr. Watanabe--who still welds the race-team pipes himself.
Development of a new pipe begins with a close study of the stock exhaust pipe from the model the system is for--manufacturers themselves are so advanced in header technology that the Yoshimura design team can often begin with that as a starting point. In many cases, the final pipe layout is determined more by packaging requirements than performance--getting the individual header pipes around the engine, radiator, bodywork, sump and suspension linkage leaves only so much room to work with.
In the design workshop, prototype exhaust systems are built by hand on the bike piece by piece. During our tour, the initial prototyping of exhausts for the race team's first GSX-R1000 was being conducted. The entire production facility is shut down for two weeks in December and devoted to fabricating pipes and components for the Yoshimura R&D race effort.
There are many aspects of an exhaust pipe that can change performance. The diameter and length of the header and S-bend tubing, the location and size of any crossover pipes (between the individual headers) and the silencer dimensions can all play a part. Once a preliminary design has been finalized, a prototype will be constructed on the bike. Dyno testing and experimentation commences, with changes made based on past experience. It all seems fairly straightforward, but there are nuances involved, and in many cases the Yoshimura staff looks to the experience of Mr. Watanabe (or even Fujio Yoshimura, who visits twice yearly) rather than computers and notebooks for answers.
Stainless steel canister tips await their fate. | 
Inner cores for silencers are rolled from perforated stainless steel sheet and spot-welded together. The race-team cores are made from titanium sheet stock. | 
Quality checks are performed continuously through the manufacturing process, and templates for every part manufactured in the shop are stored on this board for easy reference. You can see the huge number of different end caps and hangers required. With the increased size of the new facility, Yoshimura has significantly upped its quantity of on-hand stock. |