Decat my 5?

[Stig]

Hi,

Can anyone here guide/inform re;removing my cat and fitting the straight pipe.
Tell me more please!

[Geese]

Buy the correct size decat pipe.

Jack up the car.

Take of Cat Temp sensor and tie it up

Undo the bolts of the original cat

Put decat on with flange gaskets.

Done

[Steve]

have a drill + some new bolts on stand by

[fabfiveferg]

Yeah and prepare to be damned uncomfortable and sweary

[lenny_mc]

so what are the benefits of decatting? Are there any emissions problems with the nct? (mine is a 91)

[K10]

Have done it with mine, with the silenced kit from MX5parts, allegedly a lot better than the straight through kit, which makes the exhaust too boomy. Great kit, all parts, good fit etc, only comment is that there is a little play in the bolt holes at the rear, so make sure you put it back in such a way that it won't interfere with anything else (exhaust can hit the flange bolts on the LH driveshaft).

It will be a pain in the hole removing the old one though, if you have an early 5, you probably don't have a Lambda probe back there anyway. Put copper grease on the new bolts you use before you reassemble it.

As far as emissions are concerned, pre-94 cars don't need a cat (i.e. the emissions limits are loose enough). Check out the NCT manual for more details http://www.ncts.ie/nctmanual.pdf

[Stig]

Thanks all esp K10,
i'm 93, so all well NCT wise.
Steve, I take you you mean that there's a good chance the existing blots will sheer off with the corrosion?
I read I might achive an extra 10 bhp? This is probably being over optimisic ya reckon?

[Geese]

10hp a bit optimistic alright if the cat is good. If it's blocked then 10hp definetly.

Do you have the CAT heat light on your dash? if you do then there's a probe you will have to take out. You can cut the wire but then the light in the dash will stay on.

My advice WD40 the whole cat the night before the job, on the next day it will be far easier.

Also be careful with the cat, the insides are toxic. Don't sniff teh dust!

[mx5ash]

10 bhp if you couple it with a 4-2-1 header and a decent exhaust (which you already have) might be achievable, just the decat you are prob talking 2-3hp unless like geese said your old one in blocked up bad.
I had to take mine to a garge in the end and even they took an hour to get it off, and that was after some serious heat and tools being used.
I would suggest take it to someone and see if they would free the bolts/nuts for you for a resonable fee. Its not easy to get access under the car to do much to it with out a lift/ramp.

[Steve]

yeah, they might snap ... actually... you won't need the drill.. the studs are part of the cat AFAIR (?). If that is the case, snap away and get it out You have a breaker bar?
If you get stuck, a dremel works wonders

[Stig]

Thanks lads,
Yep, I have the sensor alright, but the lights not "on" on my dash.
I dunno if its worth the hassles now. Like I have a good mazdaspeed exhaust system, but if I'm only going to get 2hp or the like,its not going to fulfill my need for MORE POWER!

[Steve]

I think ya should. Then a turbo

[Geese]

I think ya should. Then a turbo

Na get NOS

[ger]

I had problems getting the cat off too, cut the nuts with an oxy torch and a small chisel in the end, didn't really care about the studs in the cat but they where fine as it happens. I felt more torque than power with a nice raspy note.

[Rhythmeister]

I noticed a drop in torque at low rev's in my wee beastie until the stainless exhaust manifold went in. THat freed up more torque and high end power than before but I;ve no dyno results before or after cos they ain't free to do!