This post addresses testing of two popular downpipes for the Mk7 GTI, a Trackslag catted downpipe and an ARM Motorsport catted downpipe. Previously the Trackslag and ARM downpipes were flow tested and also tested for how they affect turbocharger boost onset.
The GTI is equipped with each downpipe and then driven in third gear at an engine speed around 2000-2500 RPM. The accelerator is then fully depressed and held until the engine speed passes 6300 rpm.
The time for the GTI to accelerate from 3500 to 6300 rpm (47-84 mph) is measured using a Dragy datalogger.
The acceleration process is repeated a few times to generate several data points that can be averaged.
The Trackslag was tested two times, on separate days, after changing the intercooler configuration. The first time the Trackslag was tested using a stock location aftermarket intercooler, IE v1, and the second time using the same stock location intercooler in conjunction with a Majesty front mount intercooler as a bicooler.
The ARM downpipe was logged with the same IE v1 stock location aftermarket intercooler and Majesty front mount IC.
The “Valid” Dragy measured acceleration times for each configuration are shown in the table:
- TS – IE v1 intercooler
- ARM – Bicooler
- TS-Bi – Bicooler
The last row of the table, highlighted in orange, is the median time for each test case.
The data is also shown using a boxplot chart:
Evaluating the data with a t-Test to determine if the differences in acceleration times are statistically significant:
A hypothesis that there is no difference in the mean acceleration times of the bicooler test cases is rejected. The data supports the conclusion that there is a statistically significant difference in the data sets.
Looking at the turbocharger wastegate duty cycle there is a small decrease noticeable past 6000 rpm when the Trackslag is installed.
Trackslag runs are the solid lines and ARM runs are the dashed lines.
A Trackslag catted downpipe and ARM Motorsport catted downpipe were installed on a IS38+ equipped GTI to assess if the downpipe brand produced a change in the GTI acceleration times.
The Trackslag test runs were on average 0.07 seconds faster than with the ARM Motorsport downpipe. This is consistent with the flow test results and boost onset results that showed the Trackslag measured slightly more favorably compared to the ARM DP.
In this test, as with the acceleration test, the difference in measured times is small. The 0.07-second difference is approximately 2% faster.
A second test case with the Trackslag was made changing the bicooler intercooler for a single stock location intercooler. The acceleration time decreased 0.12 seconds when the single stock location intercooler was used. Interestingly, this was enough of a change to place the Trackslag behind the ARM Motorsport DP. The change from using the bicooler to a single stock location intercooler caused a greater decrease in acceleration time than the change from the Trackslag to ARM downpipe.
Note: A different turbocharger setup would likely produce different measurements. The relative standing of the two products should not change.