The Honda HRC team’s move from SC-Project to Akrapovič brought attention to exhaust systems in MotoGP. That is why they are decisive.
Paolo Gozzi / Corsedimoto.com
Honda HRC has announced that from this MotoGP season it will be using an exhaust system made by Akrapovič. The Slovenian company, which employs more than a thousand people, replaces Italian company SC-Project, which has been a supplier for the past few years. Akrapovič has a longstanding relationship with Honda: the first world championship title won by this renowned exhaust system manufacturer dates back to 2000, when it equipped the Honda VTR V2 that won with Colin Edwards in Superbike. Akrapovic also collaborates with Honda on the F1 front, where as an engine supplier to Red Bull Racing he achieved the double in 2021-22 with Max Verstappen. engineer mario uncini manganelliOral, the former designer of KTM, Aprilia and Mercedes AMG F1, guides us in exploring this vital element for performance in MotoGP.
How important is the exhaust system on a MotoGP motorcycle?
, It is seminal, so much so that two to three stages of development occur during the season. Top teams also use different systems depending on the specifics of the track: there are systems designed for fast tracks, which support maximum power. and others that improve acceleration, therefore increase torque, and are used on more twisty tracks. Weight is also synonymous with performance, so work is being done in this regard as well as on weight distribution. Design is done using 1D, ie one dimensional systems. There are very reliable programs that simulate the operation of multi-cylinder engines. In numerical simulation it is possible to identify the net performance beforehand, then to be able to design the best exhaust from a thermodynamic point of view. Work The next step is to model the exhaust in 3D as part of the motorcycle’s assembly, i.e. what is called “route piping” (twisting the exhaust) which allows for a quick and efficient assembly and disassembly. ,
What are the technical privileges of the MotoGP exhaust?
, The technology that the supplier installs is fundamental. There are parts made by plastic deformation, that is, by bending tubes using various techniques. Other parts are made by molding, especially the parts attached to the engine manifold by studs called manifolds. These are lost-wax cast titanium parts, which are very thin: they have to be extremely reliable. The supplier has an important role: a racing department can design the best exhaust, but then it has to be made right. ,
What are the main components of exhaust?
, The first element is the collector, then the primary pipes, which are usually separated. That is, each cylinder usually has a manifold and a primary pipe. Further downstream are the unions, “hot spots” in thermodynamic jargon, where flows from different cylinders of the same bench meet. Or they cross on one side and the other, according to the order of ignition. This is what controls the junction of the cylinders, although more recently we have seen exhausts whose combinations between cylinders differ in firing order. This is because you are looking for tuning of certain pressure wave frequencies that previously could not be clearly detected by the software. The pipe ends in a secondary tube and silencer.
Typically, inline four-cylinder engines such as the Yamaha and Suzuki MotoGP have only one secondary muffler. V4 engines have separate exhausts: that is, they have one exhaust with the primary a union between them and the muffler that exits down the side next to the wheel on the right side of the bike, so that in the transmission chain No interference works the other way. The collectors pass under the primary and secondary seat of the rear bench, as far as possible from the tank to avoid excess gasoline, and end in a silencer behind the saddle. On V4s, exhausts are usually bank-designed, but it has happened that a cylinder from the front bank has been linked to the rear bank. It also depends on the firing order and on the simulation experience of the technical department of each manufacturer involved in MotoGP. ,
What are the materials used?
, Usually titanium. However, the production technologies are different. The manifold is a thin-walled casting, with suitable ribs, to which the primary tube is attached by a physical connection. The tubes are bent using bending jigs obtained from the 3D model. Junctions are tubes welded together. The secondary is generally a larger tube. The silencer consists of a sound-absorbing inner part, designed in such a way that the exhaust gases comply with regulatory noise values. The exterior, ie the silencer housing, is made of carbon for track use. On the test bench, on the other hand, the exhaust system is tested for a very long time, with the engine at full load for a long time (i.e. at maximum power, Editor’s note), this is the reason why mufflers with titanium outer casing are used. Weight is more than carbon, but so is the strength. On the track, thermal stresses are less, so you can use carbon to take advantage of its lightness. ,
Is the exhaust designed by the racing department or by a supplier?
, It is still designed by the racing department, which owns the 3D model of the entire vehicle. So they are well versed with 3D modelling, which is crucial in defining the trajectory of the exhaust inside the motorcycle. But it is not excluded that top suppliers like SC-Project or Akrapovič have 3D modeling systems directly from the manufacturer. His most difficult task is to study the most feasible and customizable exhaust systems, especially from the point of view of junctions. These are the points where the manifold and primary piping are connected together, with the difference in diameter of the pipes being designed within a certain tolerance.
Then there are the connection springs which allow for flexible assembly, as the vibrations are very high. If the tube remains rigid for too long, there is a risk of cracks forming. The system is therefore usually designed in the racing department and industrialized by the supplier. ,
Is Akrapovič also a Honda HRC supplier for F1?
, I know that Akrapovič was a supplier to Honda F1 many years ago in the days of naturally aspirated engines. For now, I don’t have any confirmation. In F1, the exhaust is made of steel because, with existing turbo engines, the operating temperature is much higher than that of MotoGP engines. Cars also last longer at full load. In F1, Inconel steel alloys are used, which are said to be from the family of stainless steels. ,
How do we choose the technical supplier?
, Supplier choice is not only technical, but also related to various aspects: visibility, sponsorship, after market chain products that come out with a certain component manufactured by a specific supplier. For example, Aprilia went the opposite way from the Honda HRC: it was Akrapovic, but a few years ago it switched to SC-Project. Honda HRC probably decided to choose Akrapovič for reasons that aren’t purely technical. ,
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Paul Gozzi
