Intakerunners are the path which directs the air from the plenum to each of thecylinder. Every cylinder has its individual runner with equal length and size. Differentengines have different runner designs. For a naturally aspirated engine, therunners are usually bent while turbocharged engine have more straight runners. Agood intake runner must have low air flow resistance and in order to achievethat, the runners should have no sharp bends and smooth inner wall surface 10.
Figure2. 4: The intakemanifold constructed for Formula SAE with variable runner length 2. Oneof the significant parameter that will influence the engine performance islength of intake runners 2, 3, 9. The intake runner length plays animportant role on determining the speed and amount of air flows into eachcylinder.
Most of the car nowadays are equipped with variable intake runnersthat allow intake air to flow in different set of runners on different enginespeeds. At low speeds, longer runner length should be used to keep the velocityof the intake air as high as possible 10. The optimization of intake runner lengthcan enable the engine to achieve its maximum potential at any speed range.
Astudy conducted by Chantharasenawong in 2017 shows the effect of variableintake runner length on the performance of Formula SAE race car engine. The aimof the study is to increase the performance of Yamaha YZF-R6 600cc engine forracing application by implementing a variable intake runner length. The generalview of the intake manifold is as shown in Figure. Since it is a race carengine, the prototype of the intake manifold is installed on the car, which isplaced on a dynamometer.
The experiment is ran to determine the mostappropriate length for every speed range. The maximum and minimum length of theintake runners are 63.8cm and 39.5cm respectively, and it is tested with 11different length distributed equally between 39.5-63.8cm. The results of torquecurve for all of the runner lengths is plotted on a graph as shown in .
Thedata for the most suitable length corresponds to their range of engine speed isrecorded on Table 1. Figure2. 5:Dynamometer test results for the race car with 11 different runner lengths 2. Table 2. 1: Range ofengine speeds and corresponding runner lengths for maximum engine torque 2. Basedon Table 2.
1, the results obtained shows that suitable intakerunner length at different engine speeds are not the same. Figure show that atthe range of 5500rpm to 7000rpm, the suitable runner length cahnges frequentlyand allow optimization to be applied. In order to achieve maximum torque at anyengine speed, the intake runner length need to be vary and suit the speeds.Therefore, in order to increase the engine brake torque, at low engine speed,longer runner length are needed while shorter runner length must be used as theengine speed increases 2, 3, 10.