If You Can't Take the Heat, Don't Design an Exhaust
For the new 2012 Duke FSAE car, I've decided to redesign the exhaust system for a number of reasons. The primary reason for redesigning the exhaust system stems from the team's decision to eliminate the rear box from the frame, which shifted the suspension placement on the frame. In other words, the A-arm and halfshaft placement gave me a rather uncomfortable amount of clearance to run the exhaust through. Also, due to the shortened wheelbase, the muffler would be sticking out too far from the back of the car.
Another important consideration was passing the sound test during the tech inspections at competition. We noticed that the decibel readings varied greatly depending on which side of the car the measurement was taken, which we attributed to the valvetrain and intake noise which was recorded when the inspector stood on the left side of the muffler. Therefore, one design aspect that I wanted to incorporate into this year's car was to run the exhaust out of the side of the car in order to eliminate this extra noise to allow us to run a smaller, more free-flowing muffler. At first, I wanted to see if a dual-exhaust setup would be beneficial due to the symmetry of the design as well as the ability to run two smaller mufflers to stay within the 110 dB range. However, this design was not desirable because of the loss of exhaust scavenging when running a dual 2-1 exhaust system when compared to a properly designed 4-2-1 or 4-1 exhaust system. Therefore, I chose to stick with a 4-2-1 system due to its wider powerband and flexibility in tuning. As shown in the picture below, the major change for this year's exhaust was direting the secondary and tertiary exhaust pipes towards the front of the car.
Also, another major change for this exhaust was to make it as easy to manufacture as possible. From a design perspective, that means eliminating tight radii bends and making the pipes have as few bends as possible, all while trying to maintain the proper, equal primary and secondary length pipes determined using Gamma Technologies' GT-Power. The exhaust redesign turned out to be rather elegant, with a tightly packaged system accomplishing all of the goals I set for the project. My next step is to look into different mufflers. I believe that a smaller muffler will work for our sound goals while helping to boost performance by reducing back pressure. I also want to make the exhaust gas exit out of the side of the sidepod rather than at the front of the sidepod, but these pictures represent a "worst case scenario" in which the previous year's tried-and-true muffler can still be packaged reasonably. Overall, I am happy with this exhaust design and will be continuing to work on making the changes I mentioned. And work on designing the air induction system...