From Peter Tong]: What is the difference between the TT downpipe and the downpipe that come stock with the dual outlet manifold on earlier cars?
The length is different. The diameter is smaller. The bends are slightly more abrupt in most cases (some aftermarket replacement downpipes aren’t mandrel bent even with inner side radius’ slightly pinched in). On most of the earlier cars with cats the stock downpipes mated before the cat with a flexpipe. The flexpipe doesn’t hurt flow much but is of smaller diameter. Also the position of the collector on the stock pipe is such that it would help at higher rpm – the problem is the dp diameter is too small to support the flow at that rpm (this is from my experience). In the end count on the stock dp getting really restrictive around 115hp. When I first put my 2.0 in and was really revving it – the back pressure from the stock dp combo was so much that I blew a nickel sized hole it it! This happened even though I was running a 2″ exhaust and supertrapp rear of the cat. Kind of funny but it happened to seak out the weakest pt on my stock dp and took it out. The stock dps also have two weld
