A few days ago I swapped out my S4’s OEM exhaust manifolds for a set of the AWE-Tuning tubular exhaust manifolds.
After getting the remainder of the car put back together I began measuring some performance data with the AWE exhaust manifolds, operating in conjunction with BorgWarner RS4 K04 turbochargers.
The first question on my mind was how much, if any, affect the tubular manifolds would have on turbocharger response. I have been using the time it takes for boost pressure to build from 2 to 11 psi as a metric for comparing the response of different engine configurations.
Shown below is a comparison of the K04 turbochargers utilizing the OEM S4 manifolds and the AWE-Tuning exhaust manifolds. The K04 data spans several months, and encompasses various ambient temperatures, so I have tried to group the data by temperature conditions as this does have some affect on the turbocharger response.
Since I was preparing to take before and after measurements I was able to conduct a couple of data collection sessions in relatively similar temperature conditions, identified in the above chart as K04 (Summer) 85F and K04 (AWE Mani) 76F.
In general the slightly cooler ambient temperatures should reduce the time recorded with this metric if all other factors are equal. The times recorded with the AWE-Tuning manifolds are slightly greater than those recorded with the OEM S4 manifolds. These results indicate that the tubular manifolds decrease the turbochargers responsiveness under the procedures followed.
As a practical matter the magnitude of the slower response with the AWE product, as compared to the OEM product, may not be significant. It’s likely that the vehicle operator would have difficulty discerning a time difference requiring measurement in hundredths of a second.
Looking at this data in a more familiar format it becomes hard to distinguish between the two data sets.
The solid lines are OEM S4 and the dashed lines are AWE-Tuning.
I was also interested in investigating how the different style exhaust manifolds impacted the Exhaust Gas Temperature. I wondered if the AWE-Tubular manifolds would exhibit a generally lower EGT as a result of greater heat loss out of the manifold walls.
Looking at the exhaust gas temperatures recorded over several minutes of driving I do not see any significant difference in the trend of the EGT’s.
This initial data does not show any significant detrimental effects from the installation of the AWE-Tuning exhaust manifolds. Later investigation will focus on potential benefits that the AWE-Tuning manifolds may provide.