The pre-cat is almost certainly a particle filter.
More like a particle generator. More than one pre-cat has melted and destroyed the turbo on those cars. Generally though, it was because of a tuned ECU and low octane. (The IAM was really low so EGT was high.) Nevertheless, it's a dangerous place to put a catalyst and does measurably slow spool up.
Interestingly, despite slowing spool-up significantly, the UP catalyst doesn't cause too much backpressure once under load; removing that catalyst will lower EGT by about 50*F at the exhaust ports, whereas a full TBE will lower it an additional 150*F.
For those upgrading their exhaust, here are a few terms that might be usefull:
- Long downpipe versus short downpipe. Long dowpipe also replaces the midpipe shown in that image. Short downpipe doesn't.
- Axle back exhausts don't replace the midpipe or the resonator, but only the muffler. Catbacks replace the resonator and the muffler, but not the midpipe. A turbo back exhaust, obviously, replaces everything after the turbo.
Some other things to note are that the STi does not have a catalyst in the up-pipe, so it can be used in lieu of your stock pipe. Also, the up-pipe catalyst is very hard to see; most dealer technicians will notice its removal, but, suprisingly, many emission techs don't because it's so hard to see underneath all the heat-shields.
Also, it's a very bad idea to use an intake on a stock EJ20. The stock air-box is capable of well over 300 hp without incuring any significant pressure drop at the turbo. And, because the sensor merely attaches into the pipe, and is not a pipe of its own, most intakes change the sensor readings significantly and require engine management and a custom tune to use properly.
Also, it's advisable to get your 9-2X ECU tuned before getting an exhaust. As of 2005 the EPA drive cycle for these cars stipulates a certain amount of time spent at a stoich A/F ratio and closed loop. In some cases the ECU won't switch to open loop until 5,300 RPM which can cause audible knocking. A turbo-back exhaust system has been repeatedly shown to exacerbate this effect.
Just some food for thought I suppose.
Adrian~