Issue link: http://read.uberflip.com/i/121388
Header & Exhaust Systems Getting Everything You Can (Out Of It) The exhaust systems role in increasing engine performance centers around improving volumetric efficiency. Volumetric efficiency (VE) refers to the ability of an engine to intake and expel gases (i.e.: air/fuel and exhaust gas), in relation to the actual pumping volume of the engine. Free flowing intake and exhaust systems help an engine to achieve this. Achieving greater than 100% VE is done in part by optimizing exhaust gas scavenging to draw out exhaust and bring in air fuel mixture during valve overlap. As the piston reaches the top of the exhaust stroke, it dwells as the crankshaft sweeps across the top of its stroke. This is where valve overlap occurs. Before the piston reaches Top Dead Center, the intake valve begins to open. The trick is to design the exhaust system so that the exhaust pulse (pressure wave) leaves behind a pressure drop or vacuum to take advantage of the valve overlap. If successful the combustion chamber will exchange residual exhaust gases for a fresh air/fuel mixture before the piston has any real effect on the intake charge. To design a successful exhaust system or tuned header, the tube size and length are selected based on a list of engine specifications and application characteristics. The tube size controls the speed of the exhaust pulse, too big and the velocity (energy) is lost. The tube length is all about timing the pulse to synchronize with the cam in a specific RPM range. At the collector, the timing of the pulses is crucial to scavenging. Imagine a four lane freeway on ramp merging into one lane. If you get the timing and speed right, the pulses draft each other like stock cars at Daytona, increasing their speed. This is where the Merge Collector comes in. It makes that transition from primary tube to exhaust pipe as smooth as possible. This reduction in turbulence helps maintain velocity through the collector, thus increasing the scavenging power of the header system. If you are not sure of your header and collector design, please fill out the vehicle specification sheet available online and send it to us. Merge Collectors Cut-A-Way Views Merge Collectors have been used for many years in F1 and Indy cars. The technology has trickled down into almost all forms of professional racing. Today they have become common place and in competition, merge collectors are used wherever rule books allow. On pages 3 through 15 you will find information on merge collectors to help you decide what type is for you. If you need more help give us a call or fill out the vehicle specification sheet available online. 2 ph. 888-778-3312 www.spdexhaust.com