The September 2002 model Impreza STI was given a big upgrade & improvement. With the introduction of the twin scroll turbo charger & all stainless steel equal length exhaust manifold. With the high performance potential of the new exhaust manifold it was said that development of an exhaust manifold that could surpass the standard type was impossible. However at TOMEI they challenged that claim and they persistently tried to make that claim false. With over 10 new samples, they extensively put every single model thru its paces and thoroughly tested them. At last, finally they completed the TOMEI EXPREME Large Piping exhaust manifold which has surpassed the standard model.
For higher horsepower cars TOMEI tested all various types of exhaust pipe diameter combinations & found the best combination of 42.7mm (pre gathering section), 45mm (post gathering section), and a 45mm uppipe.
These manifolds are manufactured using a Lost Wax process designed to eliminate cracking from welded weak points and for aiding smoother exhaust gas flow without any interference. Using 2.5mm thick pipes made from SUS304 stainless steel ensure you are getting one of the best pieces on the market today.
This is a twin scroll manifold and will not bolt on to any stock USDM turbo. This unit was designed for the GD/GR/GV Chassis JDM STI's that had the factory twin scroll turbocharger. This version has larger piping and is meant for cars with aftermarket turbochargers.