Made this exhaust manifold from scratch and bare tubing. It took 90 hours of fabricating this to get it just right. The way it is designed let's the huge 70mm turbo spool up really fast when at the property rpm. It uses tight 1.5" runners to keep exhaust gas velocity at its highest and feeds into a 2.5 inch pipe that expands into a 3 inch right before the turbo t4 elbow. has a 2.5 inch feed into the other 2.5 right before the 3 expansion.