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Cat Replacement Pipe fitted on my 172 with 2 lamda sensors !

Good home required for two cats... well on a serious note I can now report what it is like to have a decat pipe fitted to a 172. Many thanks go out to my mate who did all the physical work such as welding, fitting, etc.

If anyone is interested then I can produce a "How to fit a decat pipe to a 172" in the Modifications - Exterior, Power & Mechanical area.

The car seems to have a bit more pulling power when you floor it on cam. There is an induction like noise between 2000 and 3000 rpm but its coming from the decat pipe. Cruising along there is very very little extra noise over what I had before.

In general on full throttle you definately notice a louder exhaust noise and it sounds good if you like this sort of thing.

Also the famous banging noise that many 172 owners have had has magically gone !!

The cats themselves weight quite a bit more than the decat pipe so the car is a bit lighter as well ! Also looking at the cats you notice that there are several places where the piping is very narrow indeed - I would say flow restrictive.

So how old is your car? When the time comes to get it MOTd, how will you go about it? Were the cats removed in such a way that they can be refitted?
  CTR EK9 turbo

Si - have you tried the de-cold-pipe-feed airbox trick? itl sound even better!! does it rev more responsively now? i.e. when you blip the throttle?

The car is a phase 1 - 2001 model year. I believe it has the same cats as the phase 2. Ive got just under two years before the first MOT. If it fails because of no emissions then it would take a competent mechanic 30 minutes to refit the original cats. The are attached to the manifold by two bolts and thus can be removed without doing any harm to them.

Will be heading down the M1 next Monday (26th) between 2:30 and 3:30 p.m. Shall I pop in?

Si 172
Wayne fitted a BMC air box with cold air feed to mine and his car last year and you are right it does sound really mental With the decat pipe it now sounds even more so when you floor it. I need to benchmark the car against waynes to see if it has made a difference. It feels like a rocket when you get to 5500 rpm but it might be the noise that gives that impression. It does idle a bit lumpy now and I think the car will really benefit from a Unichip which will be setup based on the mods. done.

Have you the rest of the exhaust fitted two or just the Cat rep. pipe ?
Would you be getting an extra 5 horses or so ?

  FRST and 106 GTi

SimonW, could you tell in details how this mod was made? Because I have some ppl with the problem of decating with two lama sensors...


There are several issues to overcome with the decat mod. that was made to my car.

1st of all the decat pipe is shorter than the cats. Renault changed the cat design on the phase 1 172 around December 2000. The original cats are shorter than the later ones. The original cats only support one lama sensor the later ones support two. Luckily my Magnex cat back exhaust system has a telescopic front section which sorts out the length issue.

2nd issue is the Devil decat pipe is designed for one lama sensor and you therefore need to accomodate the second one. This is achieved by drilling a hole towards the back on the decat pipe and welding in a mild steel 18mm nut with a 1.5 mm thread.

3rd issue is getting hold of these nuts. You wont find them in your local store and will need to find a fasteners that stock them.

Hope this helps.