Thomss said:
Mark have you still got the CAT on? Is there anything other silencers on it?
I Really like it!
Its got a sports cat.
You could stick a silencer in where the cat would be. Read this, quote from fmp
**Standard 182 cat is pretty free flowing as standard. De-Cat wise.....
Another reason to fit the BTB unit is a bit more technical, most people want to take the CAT off as they sap so much power, the problem is taking the CAT out and substituting a straight pipe is not really correct. OK, this will certainly give you the power back the CAT takes away through restriction but this causes another problem. When exhaust gas comes out of the cylinder it produces sound/pressure waves that travel up and down the exhaust system, if these S/P waves can be controlled correctly they can be harnessed to draw extra gas from the cylinder and so make the engine more efficient. These S/P waves are controlled by the cam timing and the pulses go down the exhaust until they meet the first expansion chamber, silencer, CAT (anything that causes the size of the exhaust bore to rise significantly). As soon as the gas reaches this expanded section, the S/P wave stops and goes back to the cylinder head, as this wave hits the back of the valve it bounces back and causes a suction pulse that helps pull more gas out the next time the valve opens. The problem is the distance from the first expanded section to the cylinder head is critical, to get this pulse action working correctly, if this distance is not correct the wave goes back at the wrong time and hits the gas coming out of the valve and so stops the gas coming out rather than helping it. This is what happens when you take the CAT out, you no longer have an expanded section in the correct place and the S/P wave will go down the system until it reaches the first silencer box before returning. Before CAT's were fitted, this was the reason all cars had an expansion boxes in a similar position to where they now fit CAT's. I know some one will say, what about the VTR with the CAT on the down pipe, or the old mini with only one silencer at the rear. The complications of how these S/P waves travel is not quite as simple as above. Lets assume the correct distance from the valve head to the first silencer should be 80 inches, providing you double or treble the distance or half it, quarter it, the S/P waves will still work their effect, so having the CAT on the down pipe or just one silencer at the back can still be right, what is practically certain is that taking the CAT out and substituting a straight pipe will not be correct and so you will loose some power.
taken from a very good tuner, talking about BTB system for a citroen saxo, which same principles apply!**
and the best one so far 
