exhaust pipe diameter, whats the diameter? Options

[ArizonaRed]

Anybody know the diameter of the 1.8L downpipe/ frontpipe coming off the manifold?

[Bitter]

well thats hard to say, the stock manifold is cast iron and would be hard to do anything to without it cracking (which its already prone to do). cast iron is hard to work with, difficult to weld, very weak when thin, it has a porus structure which makes grinding it easy but because of its porosity when it gets thin it'll crack alot easier. also, you'd only be able to port the inlets/outlet. the inside of it is like 4 short fingers that flow into a large open void. its pretty bad for scaveneging at higher engine speeds but good to keep costs low and good for....well im not sure what its good for from a performance standpoint.

making the downpipe between the cat and manifold larger with the stock header wouldnt do much..since the cat, rest of the exhaust, and the manifold before it will be restrictions.