Exhaust De-Cats

Renaults with Electronic Fuel Injection (EFi) from '91 onwards all come fitted with catalytic converters - 'Cat' for short.

These Cats are the earlier breed and not terribly efficient but when working as they should they do NOT rob 20bhp! A loss of 5bhp or so is about right. But a de-cat does free up the engine when you rev it.

However Cats do not last forever, and most of them are now in their teens now which is a long time for an exhaust component to last, especially one that gets as hot as a Cat does.

Anyway chances are the Cat on your 19/Clio/etc. has collapsed by now. You may even find upon removal someone has been in there before and smacked the internals out.

The Cat sits between the downpipe and the mid section. From the factory it was fitted with 10mm bolts which screwed into the Cat from the downpipe and the rear flange had 10mm nuts and bolts holding it to the mid section.

Now it's not exactly terribly clever to fit bolts that screw into an exhaust component subject to road splash etc but thats life. Chances are these bolts will not shift. So you need to either grind the bolt head off or cut it off with a hacksaw. The rear bolts usually cooperate better. If not chop 'em off.

Now the Cat will be off.

If it's a straight De-Cat pipe then fit it with new bolts. I use B&Q bolts, cheap, 13mm heads and easy to replace if needs be. You could get new gaskets but to be honest they are pretty rubbish so I just use exhaust sealant.

If you're planning on re-fitting the Cat come MOT time you may have a problem. Trouble is you have chopped off bolts stuck in the threaded CAT flange. These need to be drilled out or you may get away with using a blowtorch and mole grips on the bolts shank to free it. Chances are drilling is the only way.

If you have taken it off and discovered its collapsed - easy to tell - it will rattle and bits fall out and it may all be forced to the back of the CAT casing. You can remove the rest by using a broom handle on it to thump it out. This is hard work by the way.

You can either refit the hollowed out Cat back on or preferably insert a straight pipe into the CAT and tack weld it to the flange, or cut the Cat box out and just fit a straight pipe to the old flanges.

Before re-fitting clean the faces up with a wire brush, get them as clean as possible. Use a healthy amount of exhaust sealant on it, but not too much that it does inside the exhaust pipe. The bolts should be made tight as well, as you don't want any leaks.

Make sure the engine mounts are okay, if the mounts are dodgy and the rear mount has failed (especially on 19's) it opens up the downpipe to Cat join at the bottom, allowing it to blow. Other engines have a dogbone rear mount so the engine rocks instead of being strained all the time like when the 19's collapses.