:: DIY Decat Pipe ::

An easy to make DIY decat for those who do not have access to complicated machinery or welding skills. Please check the legality of fitting a decat pipe in your country, before doing this modification.

The weld free decat pipe....please note, if your cat is bolted through flange fixings you will have to cut them off the remaing pipe. This may cause problems if you need to refit the cat at any time in the future.

If you have any queries about this technical article or wish to submit your own article please email technical@alfa155.co.uk

Measure your exhaust pipe diameter, buy enough length of whatever material it's made from, to cover the gap to be left by the cat, plus a few inches spare.

Mine is 64mm o/d stainless steel, I bought a metre length.

Buy some large clamps to fit, they must be long enough to cover the old exhaust and the new insert, these were about £10gbp from ebay.

Despite the clamps being stamped as 64.5mm the bolts weren't long enough to go through the holes, plus stick out the other end.

I had to cut some longer bolts from allthread. Note the adapted washer I made to keep one nut captive and stop it turning. You could weld it on, but this is the "weld free" DIY Decat after all!

Once you've gathered the parts remove your exhaust, this picture shows the cat and end of the exhaust being trued in the vice.
Truing up the exhaust ends on the car, with a large G-clamp.

Put the front pipe back on and line everything up (use a block of wood to support each end), then measure the gap.

Mine was 220mm.

Cut the pipe to a little shorter than the gap measured; I cut this at 215mm.

Tip: wrap a sheet of paper around the tube, make sure the ends meet up and you've got a square line to cut to.

Assemble all the bits ready for fitting.
DIY Decat test fitting.

Finished, with a sealing compound (Fire Gum) applied liberally.

The mod has been running on my car for a few years now, without trouble, and has passed the UK MOT without problem.

Addendum: Since wirting this article I've found out that silicon is a much better sealant for stainless steel exhausts.

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