E46 330d 3 inch downpipe and 2,5 inch backsystem

My tuner is specialised in VAG and BMW diesel engines. out of a 1.9TDI, he manages to squeeze around 300BHP... So he figures the 3 liter BMW engines should be capable of around 400BHP. However, he strugles to get far over 300 bhp with that engine. He did however tune a 118d to the extreme for a circuit car and managed 286 out of it, which is not bad at all!!!

My personal target is not 400 bhp, but an 'easy 300'... So I thought every thing I could do to improve, I will. After the intercooler, the exhaust will get it's turn. I've bought a second hand 2,5 inch absorption silinced system with a teribly ugly tail pipe. So first thing was to have the tailpipe changed for a better looking one:




The stupid thing with the standard exhaust for this car is that right after the flexible element in the downpipe, the diameter is reduced versus the rest of the system; The outer diameter is 54 mm, which then goes into the 2,5 inch system which is about 63 mm OD. Since the exhaust gasses are hottest in the downpipe and cooler in the rest of the system and hot gasses need more volume compared to cooler gass, it is wise to start with a large OD exhaust pipe and then reduce as the gassess get cooled down. So instead of using the same 2,5 inch OD pipe for the downpipe, I made one up out of 3 inch.

First the old downpipe on the car (which I had made several years back):



Then it was time to remove it and start with the components that I had bought and made up allready.
I'll be using a hybrid turbo which has the same exhaust connections, so with the old turbo still in place, I made up the connecting pipe and welded the first bend of 3 inch on:


The connection to the rest of the exhaust is a very nicely made cone shaped piece of tube, with the bend to the downpipe attached. My muffler shop had a machine to shrink the diameter of the pipe, going from 3 inch OD to 2,5 inch ID over a length of about 40 cm:


Also, the flexible part is fitted, but not yet welded. This is how it connects to the upper part o fthe downpipe:


After welding everything up, I could nicely compare it with the old downpipe, by putting them side by side:


It's longer, because I didn't want to keep the strange bends in the exhaust where the OEM one connects to the downpipe. It's only there for the particle filter, which obviously was long gone!
The effect while driving is an even quicker spooling turbo, but regarding power output, I did not feel a huge difference (yet). It will come into it's own after the final remap!