This pipe is used to delete the "Sound Making" pipe used on Mk5 GTi and GLi's. The stock pipe splits before the throttle body and goes into the firewall to a sound maker! This extra air required to fill that tube creates additional lag. By replacing that pipe with a stock non GTi/GLi 2.0T pipe throttle response is greatly improved!

The following picture shows what pipes are deleted when the new pipe is used: