How do I decat the main Y-piece???
Discussion
As far as I know [stand to be corrected] it's quite a free-flowing cat due to it's size and I can see that any botched attempt may well block it somewhat and some report of a 'bag of marbles' sound after.
Must admit I'm tempted by Clives y piece. [note to self, must stop spending money on it
]
Must admit I'm tempted by Clives y piece. [note to self, must stop spending money on it
] 
I was considering using a cutting disc to position some alignment marks and then cutting at the weld, before removing the cat. As I don't possess any welding equipment, I was going take it down to a local workshop to have it rewelded.
I see you have a load of tape etc on your decatted Y-piece. Any reason?
I would like to consider one of Clive's Y-pieces, but it is a matter of budget. I reckon I could get this decatted for about £30 all in, which is a good compromise.
I see you have a load of tape etc on your decatted Y-piece. Any reason?
I would like to consider one of Clive's Y-pieces, but it is a matter of budget. I reckon I could get this decatted for about £30 all in, which is a good compromise.
I think it is harder than it looks, firstly when you weld something you tend to get a lot of distortion. Secondly if you cut it with a disc unless you get a uniform cut all the way around it wont go back together in the same place. To be safe I think you either a) have to make a jig to hold it at the the ends where you connect up or b) have to offer it up in the car, connect it up to the manifolds and the silencer and tack weld where you can get to and fully weld as much as possible so that you have it right. Just my opinion......
use a sharp scriber, make 3 vertical lines, at 12 oclock, 4 and 8 around the circumference of the pipe below the top weld,then get a long enough piece of card at least 2" wide and long enough to wrap around the whole of the pipe with the 2 ends meeting up to each other, position this below the weld so that it crosses over your 3 vertical lines,now, mark the pipe around the edge of the card, you should now have a straight line around the circumference of the pipe, then use a grider with a 1mm thick cutting disc, carefully cut the pipe keeping a straight line around the pipe.
remove cat, position the pipe back together, providing your cut was straight the two pieces should mate together perfectly, align the 3 vertical lines, tack weld in place, put back on car and check, if all ok weld the pipe back up.
up to you, but normally this will sound like a tractor, as you are letting the exhaust gases flow into a big dustbin like container, swirling around trying to find thier way out of the 3" pipe at the bottom, not good for flow, ergo performance.
but cheap to do if you like the sound it gives, but then you may need the cat when it comes to the mot??
remove cat, position the pipe back together, providing your cut was straight the two pieces should mate together perfectly, align the 3 vertical lines, tack weld in place, put back on car and check, if all ok weld the pipe back up.
up to you, but normally this will sound like a tractor, as you are letting the exhaust gases flow into a big dustbin like container, swirling around trying to find thier way out of the 3" pipe at the bottom, not good for flow, ergo performance.
but cheap to do if you like the sound it gives, but then you may need the cat when it comes to the mot??
chris1972 said:
I see you have a load of tape etc on your decatted Y-piece. Any reason?
.
It's heat wrap not tape, serves two purposes, firstly keeps underbonnet temps down a bit as it keeps heat in the pipework rather than radiating it outwards to other componants that might not last as long otherwise ...secondly the containment of the heat in the exhaust gasses speeds up the flow through the system..
My precats were removed by the previous owner in much the same method, as there are alignment marks scribed on the manifolds were they were cut open.
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