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If you want to improve the power output of your engine, you need to take into account the exhaust dynamics and how the exhaust can be tuned to the engine. In this article, the basic exhaust dynamics in a four stroke spark ignition engine are briefly discussed with a focus on the basics of exhaust gas dynamics. The Four Stroke Process A four-stroke engine is an internal combustion (IC) engine in which the piston completes four separate strokes. The first stroke is the intake stroke, where the piston of the engine travels down while there is an open intake valve. This allows the fresh air and fuel to fill the cylinder. When the piston is at the bottom, the valve closes and the piston moves up again while compressing the fresh air and fuel mixture. When the piston is at the top, a spark plug ignites the mixture, causing an explosion inside the cylinder, with both valves completely closed, which pushes the cylinder back down again while the burning gasses are expanding. When the piston reaches the bottom again, this time the exhaust valve opens allowing the exhaust gases to escape the cylinder while the piston moves up and pushes them out. From here they travel in the exhaust manifold’s tubes, allowing them to escape and leave room for a new fresh charge through the induction system. The Gas Dynamics When the exhaust gases travel out of the cylinder, they have a relatively high speed and pressure. The speed of the exhaust gas moving through the tubes of the manifold is different than the speed of the pressure waves created by this movement. These pressure waves travel through the exhaust manifold at the local speed of sound which can be over 500m/s in that environment, while the gases themselves move at an average speed of about 100 – 125m/s. If the manifold is not designed properly, this can lead to a large back pressure in the exhaust system and have a negative effect on efficiency resulting in a decrease of the power output. When the pressure waves reach a change in geometry, a negative pressure wave is generated in the opposite direction. If not timed correctly, these negative pressure waves could restrict the flow of the exhaust gas out of the cylinder. If this negative pressure wave is timed properly, taking into account all the variables in an exhaust system, this wave can help scavenge (draw the exhaust gas out) the cylinder and create a lower pressure in the cylinder causing the intake charge to be drawn into the cylinder better. Using a single non variable geometry exhaust pipe, one would think there would be only one occasion where the negative pressure wave is beneficial for the charging of the cylinder. However, that is not always the case. In many applications multiple step rings are used to create different resonance peaks at different engine speeds. Since the pressure waves resonate in the exhaust system, there would be occasions where the traveling of an already reflected wave creates a new negative pressure wave. This new wave would be less powerful, but could still be beneficial for the scavenging process. The effect and strength of the resonating pressure waves in the exhaust system are mainly driven by the initial pressure and the area change at geometry changes. When using a smooth transition, the effect of these resonating waves will be less than using a step ring or a collector. These are different resonance peak orders, and will reach the valve overlap at different engine speeds. When designing an exhaust manifold, many variables need to be taken into account. Luckily nowadays there are plenty of simulation software packages but often we still see that the majority of the calculated geometries are still being verified on a trial and error basis on a dyno. #Exhaustdesign #DidierDeLille #Gasdynamics

Download the special metals materials specification sheet here! Inconel (nickel-chromium alloy) is widely used for its high strength and outstanding corrosion resistance in a large temperature range (from cryogenic to very high temperatures). When inconel is heated, it forms a thick and stable oxide layer to protect itself from corrosions. Since inconel can be used in such extreme environments, it is a perfect material for exhaust components such as turbochargers and tuned exhausts used in Formula One and NASCAR or other high performance motorsport applications. Physical Properties/ Mechanical Properties Inconel 625 is the most used variation of nickel alloys in exhaust systems. It is a non-magnetic, corrosion- and oxidation-resistant, nickel-based alloy. Its outstanding performance, strength and toughness from cryogenic temperatures to over 1.000deg C are derived primarily from the solid solution effects of the refractory metals, columbium and molybdenum, in a nickel-chromium matrix. Inconel has excellent fatigue strength and stress-corrosion cracking resistance to chloride ions. Composition The strength of this alloy is drawn from the effect of adding molybdenum and columbium into the nickel-chromium matrix, meaning certain precipitation hardening treatments are not needed. Due to the combination of these elements, the metal has an unseen corrosive resistance. Machining and Welding Since inconel is a metal which work hardens, it is difficult to shape and machine using conventional methods. For example, with every machining pass, the material would either damage the tool or deform itself. At GoodFabs, we have developed a technique in our machining department where we can machine the material with a hard tool and aggressive but slow cut. An alternative to machining is to cut the material with a waterjet cutter or wire eroding. The welding of inconel is difficult, which is why we have the best welders and fabricators working for us. One of the biggest problems is that inconel is prone to cracking and segregation on the microstructural level where the heat is added to join the two pieces. #Inconel #DidierDeLille #Materialproperties #columbium #molybdenum #Specialistmaterials

Aluminium 6063 is an aluminium alloy used in most of the induction systems on high performance engines used in motorsports such as Formula 1 and touring cars or other applications which require a high strength. (Often aluminium 6061 of 6082 is used for higher strength applications). The material has magnesium and silicon as the alloying elements which gives it very good mechanical properties and makes it weldable. Physical Properties/ Mechanical Properties Aluminium 6063 is in certain tempers easily bendable because of its elongation properties which makes it an outstanding material to create induction systems with various bends and shapes. Aluminium 6030 is available in different tempers with each having their own properties. Not all of the tempered versions are as easily bendable. The tempers range from 6063-T0 with a maximum tensile strength of no more than 130MPa through to 6063-T6 with a maximum tensile strength of at least 190MPa. Choosing the correct material will be a trade-off between bendability and strength. Composition Aluminium 6063 has a good smooth surface finish and has a high corrosion resistance. Due to the addition of silicon, the melting temperature of the raw material is reduced, making it easier to weld. Machining and Welding The machining of aluminium is relatively easy and can be done on the same machines used to machine inconel or stainless steel. However, the rotational speeds and feed rates need to be adjusted to create the perfect cut. The tooling used for machining these materials is specially designed as the swarf must be efficiently removed to prevent it from bonding to the hot tool. Because of its high weldability, aluminium 6063 can easily be welded. However, in the heat affected zone, the strength of the material on certain low tempered aluminium can be reduced up to 25 to 30%. When strength is critical this loss of strength can be regained through a heat treatment process. #Aluminum #Alloys #Materialproperties #DidierDeLille #aluminum

By having full control over the entire bending process, the spring back of the metal can be controlled more quickly and cost effectively than when using hydroforming. When hydroforming tubes, variations of spring back and twisting can occur during the forming process. This can only be addressed by updating the already expensive tooling to counter this movement which can take time that is rarely available in Formula 1. Using mandrels during our bending processes, our expert tube benders can control the pressure, the speed and angles at which the exotic materials such as inconel and titanium are formed to create the perfect bend to use from a high power Formula 1 engine to aerospace components or heat exchangers. Download our tooling chart and quotation tool. Read about our tube forming and tube bending services. #MandrelBending #Hydroforming #Inconel

The welding process when fabricating exhaust parts induces some residual tensile stresses in the joints. These tensile stresses act to stretch or pull apart the material surface which might initiate a crack when there are enough load cycles. To improve the life of these welded metal fabrications, the residual stress levels in the materials (this can be stainless steel, inconel) need to be modified. This can be done using either a shot peening process or a heat treatment. WHAT IS HEAT TREATMENT? Heat treatment is a process where the metals (inconel, stainless steel, aluminium, etc.) are heated and cooled in a fully controlled environment to change their microstructure and to bring these metals closer to its equilibrium state, or bring out more of the physical and mechanical characteristics of this material. WHY ARE STRESSES PUT IN THE MATERIAL? The residual tensile stress from welding inconel, stainless steel, aluminium, etc. is created because the weld consumable is often applied in a liquid state. The welding process consists of heating up the metal, then the weld is applied in its hottest, most expanded state. When the much cooler consumable material is bonded to the base material, the weld tends to cool rapidly and will attempt to shrink from the drop in temperature. Because the base material is usually much stronger and not in a molten state, this cannot shrink, leaving the material remaining in a highly stressed “tensioned” state. This zone is usually just next to the weld joint, which explains why a crack usually appears “right next to the weld”. TYPICAL HEAT TREATMENT BEHAVIOUR The graph below shows a typical situation of a welded metal component before and after heat treatment. As can be seen from the graph, the residual stresses in the welded metal such as inconel, stainless steel, etc. are positive, which puts the outer surface layer in a tensional state. When the metal is heat treated in a controlled environment to stress relieve the residual stresses, we can see that the metal reaches an equilibrium state and the residual stresses are close to zero. This graph does not refer to any specific material and is purely for illustration purposes. COMBINING HEAT TREATMENT WITH SHOT PEENING Heat treating an exhaust system can enhance its properties. Annealing can soften a part and make it more flexible and less prone to cracking, while other treatments may make it stronger. Heat treatment is typically carried out overnight although some process may take significantly longer. When combined with shot peening , which sometimes follows heat treatment on same day, the material properties could be enhanced even more, as illustrated in the above graph. #stainlesssteel #Inconel #aluminium #stress

GoodFabs has recently bought a plot of land and been awarded planning permission to extend its Motorsport Valley workshop on the Crendon Industrial Estate. Building is due to start in the Spring of 2017 and the extension will allow for greater capacity for fabrication, machining and heat-shielding, as well as improved inspection and quality facilities. #GoodFabsworkshop #Crendon

GF Moto are showcasing our new ultra-light exhaust header systems for the first time at the MCN London Motorcycle Show at Excel in London on 17-19 February 2017 on Stand No R111. Come and see our new ultra-lightweight exhaust headers for the Honda Africa Twin and BMW S1000RR. Both exhausts are made with super light materials and are designed and fabricated to F1 standards featuring hand-made pressings and welding rarely seen outside the world of top motorsport. Both the equipment used and the fabricators themselves will be at the show to talk about how these limited edition systems were designed and made. #MCNLondonMotorcycleShow #HondaAfricaTwin #BMWS1000RR

Although we work for a number of F1 teams, we are tightly bound by confidentiality. Not only can we not discuss what we do, but in most cases we can not even reveal who we work for. HRT withdrew from F1 in 2012 so we are at liberty to use them as a case study to illustrate the sort of program that we run for race teams. HRT began life as Campos Meta in 2010, as one of the three new teams to enter F1 using the Cosworth engine. The first systems were designed in collaboration with Dallara, who built the first car. Dallara designers used our tooling chart to see what diameter tube that we could bend and what centre line radiuses they could use to route the primary pipes. Following agreement on a CAD model we had to make the system from scratch in a two week timeframe so that the new team could enter the first race in Bahrain, having missed all pre-season testing. Both cars started from the pit lane. Just before the first race, Campos became Hispania Racing F1 (HRT) and Colin Kolles replaced Adrian Campos as Team Principal. In May, Kolles took over the car's development from Dallara. In 2011 Good Fabs were asked to redesign the exhaust system. Based on his 20 years experience fabricating F1 exhaust systems using Ferrari, Mercedes, Cosworth and Renault engines, Phil Levett worked with design engineer Didier de Lille to design a new system that would improve gas flow while avoiding all surface issues dictated by the bodywork's aerodynamic surfaces. The new system used the same inconel 625 material, although in different wall thicknesses depending on proximity to the engine. New steps were introduced to increase the diameter as the primary pipes approached the collector and the tailpipe was redesigned. The first design was approved for production. However, during fabrication some adjustments were suggested to optimise the manufacturing process. These minor alterations were recommended to reduce both production time and cost. GoodFabs built and scanned a finished system, created a new CAD model for design approval and the new design was passed by HRT for production. The GoodFabs exhaust system was used in 2011 and 2012 seasons, did not fail once and enabled HRT to consistently finish races. Most systems were used for two races and were not shot peened - a finishing process used to stress relieve welds. Based on orders placed towards the end of 2012 it is likely that the final systems were run for four races. Many teams, including some toward the back of the grid, replace exhaust systems every race. #HRT #CamposMeta #HispaniaRacingF1 #PhilLevett #DidierDeLille #Inconel625

As part of our decision to extend our fabrication and machining capabilities outside the world of motorsport, we have created a limited edition titanium header system for the Honda Africa Twin, a bike that we really like and think deserves a special set of pipes to bring out the best exhaust note. ​ Press play to hear what it sounds like in a dyno cell: Press play to see what RJ at Royal Jordanian thinks of it: If you are interested in finding out more, send us an email to info@goodfabs.com. #motorbike #HondaAfricaTwin #titaniumexhaust #RoyalJordanian

GoodFabs is the winner of Buckinghamshire's first High Performance Technology & Motorsport (HPTM*) Business of the Year award. The Aylesbury-based company was announced as the winner of the award - sponsored by Silverstone Park - at last night's glitzy Buckinghamshire Business Awards ceremony. Presenting the trophy was MEPC's Roz Bird, Commercial Director for Silverstone Park. Other finalists were Silverstone Park company EDM Precision and Monodraught, based in High Wycombe. GoodFabs is a world-leading expert in shaping, fabricating and welding thin wall alloys, in particular Inconel - a specialist nickel alloy that performs at very high temperatures. Many major championships and motorsport teams - including those from Formula 1 - use its products. Demand for its skills in America's world-famous NASCAR category has also led to it opening a US branch. MD Neil Morgan commented: "This is fantastic for us. Coming first in such a high-profile category - particularly in Buckinghamshire which is among the biggest commercial counties in Britain - really is a big deal. "In top motorsport you only tend to get noticed when your product suffers a failure! So this is great recognition of how we've gone about working in an industry for over 30 years and of the investment we've made in people in the company. We've got 30 very talented, hard-working fabricators, machine operators and engineers. "To be associated with an award sponsored by Silverstone Park adds massive credibility and kudos - it's a name recognised in the world of motorsport and increasingly in high-tech engineering." "Our award is all about discovering the best-performing HPTM companies in Buckinghamshire, which is an integral part of the Silverstone Technology Cluster. The county has a glowing reputation for producing some of the finest engineering companies in the UK as well as developing new talent in the technically advanced fields that are so crucial to industries such as marine, aerospace, defence, medical devices as well as motorsport. "The competition therefore to win this award was always going to be fierce making Good Fabrications an extremely deserving winner." *The term HPTM is defined as anything from software design to advanced engineering and everything in between including electronics, CAD, manufacturing, R&D and the professional service companies that support these activities in sectors such as aerospace, medical devices, defence, marine and motorsport. #BuckinghamshireBusinessAwards #SilverstoneTechnologyCluster #HPTM

GoodFabs exhibited at the Professional MotorSport World Expo (PMW) in Cologne (11 - 13 November 2015). We displayed our capability to combine a full DMLS collector onto a completely fabricated exhaust system. As the environment becomes more and more important, we were proud to be part of the panel discussion on exploitation of exhaust gas energy recovery. The panel included: Didier De Lille, design engineer, GoodFabs (UK) Alex Hitzinger, technical director LMP1 Project, Porsche (Germany) Jaap van der Lee, turbocharger specialist, Van Der Lee Turbo Systems (Netherlands) Peter Albert, executive vice president, Jaquet Technology Group AG (Switzerland) #PMW #Expo #DMLS #DidierDeLille #ProfessionalMotorSportWorldExpo