Just got a custom SS exhaust and cat bypass kit fitted today. Made a big difference to the sound, it sounds like a rally car now especially on the over run. I couldn't really try the performance too much as the roads were too busy, but I am sure there will be an improvement looking at how restrictive the CAT is. I will probably need to get a high flow CAT for my MOT next year, but I have been told I may be able to pass without due to the greater efficiency of the TBs and MBE so I think I will get my car on a gas analyser first to see what the score is. I will need to get a lambda sensor sorted out however, as I am running lambda less at the moment. I have been told you can use the bosch sensor from the astra and that it is compatible with MBE. Does anyone know if it will fit the corsa exhaust manifold, and how to wire it up.