## 4 Results and Discussion  
### Analysis of the Measured Back Pressure  
In the back pressure measurement experiment, the pressure of exhaust gas inside the actual exhaust pipes was measured using the pressure transducers. As a result of checking the temperature of Bank 1 (Catalytic converter) using a vehicle scanner during warm-up according to the procedure in Figure 4 before measurement, the temperature increased from about 85 \({}^{\circ}\)C to about 300 \({}^{\circ}\)C.  
Figure 5A-C show the time series plots of back pressure using the data measured at measurement positions 1, 2, and 3 for approximately three minutes. In the measurement state, the sampling interval was 50 ms. In the measurement results, H Pipe exhibited the highest pressure at measurement position 1, Y Pipe at measurement position 2, and H Pipe at measurement position 3. Based on the measurement results, the analysis of the time-series plots revealed that X Pipe had the highest standard deviation (0.773) at measurement position 1, Y Pipe (0.227) at measurement position 2, and X pipe (0.189) at measurement position 3. As for the lowest standard deviation, Y Pipe had a value of 0.625 at measurement position 1, X Pipe had a value of 0.174 at measurement position 2, and H Pipe had a value of 0.158 at measurement position 3. Figure 4: Schematic diagram of the measurement procedure for exhaust emissions. \begin{table}
\begin{tabular}{c c} \hline
**Description** & **Specification** \\ \hline Measuring item & CO, THC, CO\({}_{2}\), O\({}_{2}\), \(\lambda\), AFR, NOx \\ Measuring method & CO, THC, CO\({}_{2}\): NDIR, \\  & O\({}_{2}\), NOx: Electrochemical cell \\ Repeatability & Less than \(\pm\)2\% FS \\ Operating temperature range & 0–40 \({}^{\circ}\)C \\ \hline \end{tabular}
\end{table} 
Table 5: Specifications of emission analyzer. Figure 5: Results of the time series plot for back pressure measured at measurement positions 1, 2, and 3. Therefore, the standard deviation was shown to check the spread based on the arithmetic mean value in each of the measured back pressure results shown in Figure 5A-C. The standard deviation result at the measurement position (A) showed a relatively higher value than the result confirmed at the measurement positions (B) and (C). This result is shown because it is directly affected by the exhaust pulsation, and it is confirmed as a position that can be affected by the valve overlap. Moreover, the standard deviation was decreased at the measurement positions (B) and (C). From this result, it can be seen that the exhaust pulsation caused by the exhaust gas confluence was stabilized. Figure 6A-C show the time-series plots of back pressure at each measurement position using the average data of three measurements performed for approximately three minutes and the total mean values. Figure 6A shows the results measured at measurement position 1. The first, second, and third measurements showed that relatively high pressure was applied in H Pipe and relatively low pressure in X Pipe. H Pipe exhibited the highest mean back pressure of 0.273 kPa. Y Pipe showed 0.245 kPa, which was approximately 10.3% lower, and X Pipe showed the lowest pressure of 0.169 kPa, which was approximately 38.1% lower. Figure 6B shows the results measured at measurement position 2. The first, second, and third measurements showed that relatively high pressure was applied in H Pipe and relatively low pressure in X Pipe. H Pipe exhibited the highest mean back pressure of 0.362 kPa. Y Pipe showed 0.321 kPa, which was approximately 11.3% lower, and X Pipe showed the lowest pressure of 0.144 kPa, which was approximately 60.2% lower. Figure 6: Results of arithmetic mean values for back pressure measured at measurement positions 1, 2, and 3. Figure 6C shows the results measured at measurement position 3. The first, second, and third measurements showed that relatively high pressure was applied in Y Pipe and relatively low pressure was applied in X Pipe. Y Pipe showed the highest mean back pressure of 0.288 kPa.