Have you removed your Cat/DPF/pre cat


Staff member
Deal, Kent UK
A3 1.4 TFSI 150 COD
How many on here have removed their Cat/DPF/pre cat?

Was it a good mod? Do you notice a power/response difference from it?

What about sport cats or high flow alternatives? - I had a sports cat and this was quite impressive, I couldn't tell between this and no cat at all!
I was going to remove the DPF but decided to keep it with all the new MOT regulations here now and getting stricter in near future.
My GTR already had its cats removed and being registered in March 1995 meant it didn't need one for MOT. Can't comment on whether it made a difference but they were supposed to be 280bhp standard and with this being the only mod it Dyno'd at 355bhp so they removal must of helped.
My old 944turbo was to old to have a cat (*˘︶˘*)
I will be on this car, I think there's one in the DP and one in the mid pipe (need to double check which to remove) but I'm 99% sure I can de-cat the DP when I go for 3" then fit my old race cat in the midpipe, or it's the other way around! but I can ditch one and race cat the other.....then remap as it'll probably throw a CEL

Tbh I didn't notice that much bar a little more noise decatting my older car, I ran it like this for the year then fitted the race cat to save the hassle MOT time.....no noticeable difference here either but the car was a much lower state of tune at this point.
I decatted the MG several years ago, made a difference with the noise and also made a slight improvement on the final figures, breaths better. I had to fit a MIL kit as the light was temperamental. The OE manifolds have a pre-cat and it is this that ensures it passes the emissions. Aftermarket manis means a sports cat is needed to pass the MOT and the gains are not as much as the remap so left that mod alone as also too costly. Never saw the point in the post-cat as this showed it was belt and braces.
removed the cat on my blue 306 since it wasn't required by law, fortunately for me at the time, pug sold the early 306 dt's without a cat from the factory so I just bought the front section of the exhaust for 20 quid and had my local exhaust centre fit it for me,
I wouldn't say my top end improved (probably because of the governor in the injector pump) but id had a noticeable hike in midrange shove and the turbo spool a little earlier in the rev range, and I saw a slight improvement in fuel consumption when paired with an egr delete
mot wasn't affected since it wasn't required to have one to pass,
I know I bang on about the Fuel Cat but the proof of the pudding is in the car tax ! By putting a fuel cat in the fuel line just before the injection unit to firstly reduce carbon build up but mainly to get more MPG, which I do, but I now pay £145 car tax instead of £225, the guy at the mot centre retested his co2 thingy on another car 'cos my Focus tddi was so low he thought his machine was busted, so if you fit a fuel cat in the tank or in line you can then remove the exhaust cat & still pass the mot. simples.
There's another forum I visit for my car, but the advice they give is usually suspect, so i wanted a second opinion. My car has a primary cat that I won't touch, but further down the line, well after the O2 sensor, there's a secondary cat. Where I live there's no emissions testing :}> Should I gut the 2nd cat?

At the other forum they seem to believe that you have to buy a test pipe because a bulge in the exhaust is worse for gas flow than trying to breathe through a brick.... which I have a hard time swallowing.
The secondary is actually the main cat. This is the 3 way closed loop cat and it the one that should stay in place. The upstream one is a 2 way unregulated oxidation only cat. Its primary function is to protect the regulated (main) cat and the O2 probe(s) from unburnt fuel and high doses of CO. It's a good system.

If there's no emissions testing and you're not going to be hit at the roadside for high noise levels then remove the whole lot. This will almost certainly require ECU remapping.

Personally I'd leave it alone because I like to abolish noise. But this is purely my personal preference.
There's no O2 sensor downstream of the secondary cat. the primary cat has an o2 sensor downstream and removing it will trigger a CEL plus it'll mess with the warranty.
Some cars run a three way closed loop arrangement with a single probe positioned as yours is. This was the norm before Euro IV petrol emissions standards came into force. However, you're a fair way from Europe - I am not sure what the rules are in Florida. There might also be some federal legal requirements that have to be met in addition the Florida's own rules.

This is why I mentioned an ECU remap, basically to program out the O2 probe and leave the ECU to manage fuelling solely under control of the MAF and other sensors, without triggering the CEL/EML warning. Warranty would be an issue though, sadly.

Are you sure the manufacturer will be OK with the aftermarket exhaust arrangement?
As long as you don't mess with the BPV/turbo/o2 housing it's fine with Hyundai. There's an law in the US, a federal act from the 70's, that protects car modding. So unless they can prove that what I did blew up the engine or component, they have to honor the warranty. ECM remap voids the warranty too. So I'm going to drive up to 60k miles AS FAST AS POSSIBLE to use up the warranty so the fun can begin! :woot: ECM remaps are available (either custom tunes or canned) and they really ramp up the power so I want my exhaust to be able to handle 300 HP which is my eventual goal. For now I want to get the exhaust and get what little benefit I can from it without a tune. The ECM apparently adjusts to changes and to your driving habits, but it always runs on the rich side for safety.

This car has no MAF, it's a MAP sensor. It has a stock wideband AFR sensor standard and I don't think it enters closed loop mode. Older models did because the AFR sensor in those cars was narrow band. I'm not 100% sure whether it enters closed loop even with the wideband sensor, but I think it does not.

There's a federal law about deleting cats. But there are no random checks, no inspections here in FL either so the law is not enforceable. On the Federal level there is no framework in place to check either.
Ok people listen up, yes you CAN remove your catalytic converter, BUT you must , for emissions at the MOT, replace it with another type of fuel emission unit, the best on the market is the Fuel Cat, this small unit allows you to remove your exhaust converter but still give low enough emission numbers for most cars to pass the test, check the units out & decide, will it or wont it !
And here comes my beautiful country with dysfunctional car control system. It is easy to pass control - you have to have friend who is owner of vehicle control station...
Ok people listen up, yes you CAN remove your catalytic converter, BUT you must , for emissions at the MOT, replace it with another type of fuel emission unit, the best on the market is the Fuel Cat, this small unit allows you to remove your exhaust converter but still give low enough emission numbers for most cars to pass the test, check the units out & decide, will it or wont it !
This is similar to the sports cat, it stays within legal parameters without restricting the exhaust flow too much. Personally I can't see the point of switching in and out an item just for the MOT especially when there is the real risk of a roadside spot check.
Dear Waynne ! how you fit the cat is as follows, cut the fuel line, insert the Fuel Cat between the line & secure with fittings provided, hey prestow, you now , ( on a normal car ), have two catalysts on your car, the fuel cat cleans the inside of the engine, not just the fuel being used, one of its main uses is to get rid of carbon deposits from the burnt fuel aswell as all the other advantages. may I suggest that a 50p phone call to Fuel Cat will give you all the details, I only know a minute amount of what these units are capable of. Million's of pounds worth of orders from the US army says it all. Give the guy a call, he's a scientist !!
I've also got a MK1 Range Rover to which I've fitted a Fuel Cat & Formula Power 10mm carbon HT leads, these together give a more complete fuel burn, also when sitting in traffic jams carbon build up in worse than when driving, the Fuel Cat catalyst stops the build up of harmful carbon deposits so making the engine rum much more efficiently & obviously your MOT doc will show a reduction in carbon emissions which may drop you older/high mileage car down in car tax.
Because I've fitted both items to my 3.5 injection V8 after 3 weeks of running her I've noticed a dramatic increase in power.
PS. instead of £59.95 for an upto 3500cc Fuel Cat the price is now on special offer at £39.95 inc VAT................cant be bad.....

Please watch this on my YouTube channel & Subscribe.