GVK.

This post about de-catting a Focus ST

https://passionford.com/forum/genera...t2-de-cat.html

OP wants to de-cat his Bluefinned ST because 'the cat is restricting the power' and put out 227hp.

I would suggest it has other problems such as low boost pressure/boost leaks or whatever before the cat is the restriction at that power level.

Discuss!!

gjh

Ye I doubt they are that restrictive any more, reckon most cars after about 2000 probably have quite good flowing cats (no sort of proof here though, all theory).

RichieST

iTrader: (2)

No, I don't think they are. They may restrict a couple of BHP however for the hassle they cause it isn't worth the bother. I've got a sports cat on mine and I noticed absolutely zero difference. I'm thinking about putting the standard cat back on and selling it as I'd rather have a bit more cash in my pocket!

jamie's

defo not as bad as they used to be, still restrict it a bit obviously,
but if its stuck at just 227bhp then its never the cat thats the prob at that power
theres plenty doing much higher numbers than that with the cat still on
only way a cat will be restrictive at hat power is if its collapsed inside or something
a perfectly working cat will flow more than that no prob

CrOwSoN15

It's restricting flow, so yes they are restrictive, but as has been said, probably a few horses at most.

botters

iTrader: (2)

cats are just as restrictive today as they have always been very little has changed about their design except materials used the exhaust gas still has to travel through thousands and thousands of tiny little holes instead of one large pipe. however the cat is not the problem with that guys car

Cossie Sean

this goes deeper than limiting power, these are designed to have particular backpressures/flow rates for the map on driveability stakes etc

removing the cat will help gain power once the map is tweeked, granted.

you could say the same thing about the fuel injectors and such likes,
how much time you got? lol

pani_k

iTrader: (1)

As I said on that thread, I think the fact that it has a Stage 1 map and can't get above 227bhp is because it doesn't have an uprated intercooler, otherwise there is something else wrong with it.

I haven't tried a sports cat or decat, I have just a Mongoose Cat-Back with standard cat and downpipe. IMO the cat and downpipe should be changed together and preferably if you go sports cat, you get the least restrictive you can find and if you are going to the trouble of removing the cat, you simply decat it as most developer maps make the most of their power utilizing a decat. I suppose it depends on the engine in question as well but the cat on the ST is quite chunky.

GVK.

Might be running feck all boost too (boost solenoid failure?)

pani_k

iTrader: (1)

Nah, he's just running a remap and that's it, no intercooler! With temps the way they are I wouldn't be using boost at all without a proper one! The ST one is more at home on a small commercial van!

GVK.

Yeh, it is a bit tiny, I know the Pro Alloy ones as part of the Mountune kit are huge in comparison.



(can't find a pic of the two together to show the size difference)

Glenn_

iTrader: (1)

When I took the cat out of my old 2ltr sierra hatchback it defo felt quicker.Bloody horrible cats.

GVK.

Note I said modern Glenn.... I agree the early 90s cats were probably more restrictive.

Glenn_

iTrader: (1)

Sorry boss.Surely if you replace any cat on even newer cars the car is gonna be quicker.I just think if all the exhaust gasses that are trying to get out the exhaust and with the inside if the cat like honey comb it gonna be restricted?????? Where if there is no cat the exhaust gases are gonna be more free flowing???

jamie's

a bit exhaust back pressure can be a good thing

alistairolsen

No cat will always be less restrictive than a cat, it's impossible for it not to be really, but its a tiny percentage and really not worth the legal and MOT hassle.

GVK.

You don't want any back pressure on a turbo car, that's why the exhausts are generally larger with less boxes than a NA car (the turbo itself reduces the sound energy from the engine)

Back pressure as a subject...Is a lot more complicated than that though.

I'd like to see some proper before/after proof of de-catting on a dyno test, I bet it's marginal at most.

pani_k

iTrader: (1)

Airtec Gen 3 vs Standard. It's also about 40% larger in depth too!

Also you can see in this pic (just) the size of the cat on the ST. Imagine having a straight pipe in the place of that massive thing!

GVK.

Thanks for this pics.

jamie's

exhaust back pressure can help keeping a turbo healthy
the turbo itself relies on a bit of back pressure to operate efficiently
but my remark wasn't realy aimed at turbo engines, just a general statement

Carlos-Titx

My old one made 284 bhp with a standard intercooler and decat and was running spot on with a DS map (I know figures vary from one RR to another).