scott87 Posted October 10, 2012 Share Posted October 10, 2012 I was just wondering what the real difference is in having a 3" 2nd decat over a 2.5" other than the obvious being size. I have just received mine and went for a 3" but im just wondering. Quote Link to comment Share on other sites More sharing options...
Littler Posted October 10, 2012 Share Posted October 10, 2012 Decreased back pressure would be a result which is not good for an NA Quote Link to comment Share on other sites More sharing options...
scott87 Posted October 10, 2012 Author Share Posted October 10, 2012 Decreased back pressure would be a result which is not good for an NA Half an inch will surely not make that much difference? Im putting the 2nd decat and that is it, keeping the rest of the exhaust standard. Quote Link to comment Share on other sites More sharing options...
dan294 Posted October 10, 2012 Share Posted October 10, 2012 Are you leaving the first CAT in? Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted October 10, 2012 Share Posted October 10, 2012 Stick it on a dyno and find out Quote Link to comment Share on other sites More sharing options...
scott87 Posted October 10, 2012 Author Share Posted October 10, 2012 Yer leaving first cat in. The exhaust will stay standard silencers until after winter when my exhaust has finally given up. But having the decat fitted tomorrow. Was just worried it may not fit but im assuming it will if you can buy 3" or 2.5" decats. Quote Link to comment Share on other sites More sharing options...
Noz Posted October 10, 2012 Share Posted October 10, 2012 You won't loose that much backpressure if your exhaust system is 2.5". My NA ran 219bhp with 2.5" exhaust and 3" decat and a panel filter. It may lower overall backpressure but wouldn't make a huge amount of difference as you still have the exhaust system giving a bottle neck creating a disturbance in flow which would in itself create even more resistance and more back pressure. Obviously not as much as a 2.5" decat. But in general.. I wouldn't worry about it. Quote Link to comment Share on other sites More sharing options...
scott87 Posted October 10, 2012 Author Share Posted October 10, 2012 You won't loose that much backpressure if your exhaust system is 2.5". My NA ran 219bhp with 2.5" exhaust and 3" decat and a panel filter. It may lower overall backpressure but wouldn't make a huge amount of difference as you still have the exhaust system giving a bottle neck creating a disturbance in flow which would in itself create even more resistance and more back pressure. Obviously not as much as a 2.5" but changing from 3 to 2.5" will cause a little, probably no even noticable but still there. I wouldn't worry about it. Cool thanks. I will get it fitted tomorrow then :-) Quote Link to comment Share on other sites More sharing options...
Nic Posted October 10, 2012 Share Posted October 10, 2012 Yer leaving first cat in. The exhaust will stay standard silencers until after winter when my exhaust has finally given up. But having the decat fitted tomorrow. Was just worried it may not fit but im assuming it will if you can buy 3" or 2.5" decats. The 1st cat is the most restrictive of the 2, fitting a 2nd decat pipe will make it a little louder I doubt it'll make any significant difference to the performance though. Quote Link to comment Share on other sites More sharing options...
scott87 Posted October 10, 2012 Author Share Posted October 10, 2012 The 1st cat is the most restrictive of the 2, fitting a 2nd decat pipe will make it a little louder I doubt it'll make any significant difference to the performance though. Its not a performance upgrade im looking for, just a better sound and the fact that all of the pipe and heatshield is rattling to buggary under the car, which has been driving me insane. When i get a ss cat back system should i go for a 3" so that is matches the 2nd decat i have. Quote Link to comment Share on other sites More sharing options...
scott87 Posted October 10, 2012 Author Share Posted October 10, 2012 Also why are there standard exhausts that dont have the twin silencers? Ive seen one or two in photos. As ive gone for a 3" decat, how does this connect, will where it bolts to the standard exhaust back not be smaller or is it 3" as standard? Quote Link to comment Share on other sites More sharing options...
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