DE-Cat questions

[FD3S Efini]

im tempted to de-cat my rex (on top of the other toys im fitting when i get itback) im just asking how easy it is to de-cat an what needs to be done? is it a simple case of just removing the cat and putting a straight through pipe on and the mapping it? also will my racing beat exhaust be able to be de catted?
 
im new to this so please explain in the simpliest terms lol
 
Thanks
 
Kris

[FD3S Efini]

by the way the car is a 1994 fd if that helps?

[m1tch]

Yeah, a decat pipe usually is just a pipe with flanges at each end like the cat had, don\'t forget that the cat also acts like a midbox, so will be louder will a decat, and im glad you have mentioned mapping

[FD3S Efini]

so it is litterally a case of just bolting the new pipe on with the correct gaskets and away you go? apart from mapping is there anything else that need to be done?
 
Also has anyone here got a decatted racing beat exhaust video they could upload as i wouldn\'t mind hearing it without the cat.
 
Cheers again
 
Kris

[Jovic82]

i have a racing beat exhaust with a silenced decat and it is still pretty loud. when decatting some people experience what is known as boost creep as a result though. not trying to put you off just be aware that it isnt always as straight forward as just changing one thing

[FD3S Efini]

whats boost creep? and how do you get rid of it?

[m1tch]

Boost creap is caused by the fact that the exhaust is much free-er flowing meaning that the exhaust can escape the turbo much easier, unfortunatly the wastegate on the turbo won\'t be big enough to be able to get rid of all this extra gas flow causing the exhaust gasses to \'back up\' this means that the turbo will keep spooling and the boost will creap up as the turbo can\'t get rid of the exhaust gasses quick enough, think of it like a sink of water, with the tap on the water can easily escape though the plug hole, this is how it was as stock, now replace the tap with a firemans hose, but keep the same small plug hole - the sink will fill up faster than the water can drain away.

This can be countered by having the turbo ported and the wastegate modded to allow better flow, on my car I had a full turbo back exhaust on my car, but stock turbo, on the 5psi wastegate spring it boosted to about 10psi lol luckliy my car was mapped higher than that, else the engine would have gone as the mapping would have run out at that boost level.

I have also had a custom open mouthed downpiipe made - the only 1 ever made for an FC, which allows the wastegate to fully open, rather than opening about 8mm as the stock wastegate setup allows lol

Becuase the decat reduces the back pressure (pressure stopping the turbo spooling) the turbo will now boost creap, its best to get the mapping sorted and also get the turbo ported as without a ported turbo - or at least mods that allow the wastegate to work properly you won\'t be able to control the boost properly - even with a boost controller as the boost controller controls the boost using the wastegate, if this doesn\'t work properly, it can\'t control the boost lol

Hope that helps

[FD3S Efini]

that helps alot mate cheers for that it was a good read.
 
Kris

[Aubec]

You\'ll also want to disconnect and blank off, or remove the airpump if you are de-catting.  In the stock set up there is a pipe from the rear of the engine that runs to the cat to provide it with extra air at low revs.
 
Oh, and forget about passing the MOT without a cat if you dont have a very understanding garage you can use.

[m1tch]

You\'ll also want to disconnect and blank off, or remove the airpump if you are de-catting.  In the stock set up there is a pipe from the rear of the engine that runs to the cat to provide it with extra air at low revs.
 
Oh, and forget about passing the MOT without a cat if you dont have a very understanding garage you can use.

The cat doesn\'t need to be in place for an MOT, will need to pass emissions though, which is why mine has a CO of 0.45% with the air pump, cat is there for emissions, you can pass without the cat

This is from the MOTester.co.uk webiste:

"The MOT regulations say nothing about a vehicle having a catalytic converter. They merely set emission levels which have to be achieved if the vehicle is first used after a specific year. Certainly some cars with every efficient engines could achieve the required emission levels without a catalytic converter. However in your case, if your vehicle’s year is before the break year, then should the cat be removed, in all probabilty it should not affect the MOT"

[Aubec]

Emissions are part of the MOT test though.  The age of the car and whether its an import or not will affect the numbers you need to hit however - I dont believe there are many modified FD\'s legitimately passing MOT.  You can struggle to hit the numbers on an unmodified UK FD with both the pre-cat and main cat in place...
 
That said, people claim to have made the numbers by leaning out the engine using their PowerFC - most I think just go to a liberal minded garage.

[L18M]

im sure hteres many friendly mot testers but i dunt know many :p
thames valley in reading, FCM MOTORSPORT i believe do mot (in bristol, not sure how far it is from u but sure closer than reading lol) details for them can be found on sj-cc.net

[neil_jdmr]

Like everyone else has said, Dont be tempted to bolt up your de-cat pipe since its a real easy job then go out and give it the beans as many MANY fd\'s have met their demise this way.
I left my cat in place till i was at pip\'s then we both swapped it and i let pip work his magic with the mapping. Also doing it this way allowed me to get a dyno run before cat+mapping so i had a clear view on the gains the mapping provided.
 
Just the de-cat and a hks downpipe and uprated smic over stock and with pips conservative mapping i drove in with 247bhp and 210lb\'s/ft and drove out with 306bhp at 0.8bar or 326 bhp at 0.9bar which is switchable on the commander although i leave it at 0.8bar most of the time although i have used the 0.9 bar setting over this summerbut have changed back now to keep inj dty in the high 80\'s instead of low 90\'s.
 
As for mot i have kept my airpump etc and just blanked off at the cat end just incase i needed it for mot and i can say as soon as you change/remove any part of the stock exhaust system IT WILL NOT PASS!!! tbh i cannot see a complete stocker passing.
 
Also i have a with my exhaust system dp/de-cat/nurspec it is very loud on town driving but not so bad on boost.

[m1tch]

I am still running my airpump and will be changing to the corvette electric smog pump when I change the turbo same effect, more space lol