New MOT - Fake cat?

[Greedo]

So, as everyone knows after about 200 threads on the subject, the MOT laws have changed.

One of the changes mean you MUST have a catalytic converter in place, if your car came with one from the factory, whether or not it will pass an emissions test without one.

So, is anyone else considering fitting some kind of dummy cat incase of a road-side stop check? How would you go about it?

Obviously, you're not going to pass an emissions test with this in place - but if your car has been mapped for low emissions or you know a friendly MOT'er, a cat is just going to hold your performance back.

[Mochachino]

MOT testers dont do road side checks, and if the police or vosa do, just point at the silencer and say its a cat, or say its in the manifold. The police dont jack your car up and start dismantling it.

[Greedo]

I still think its a viable idea. A fake Cat isn't going to fool an MOT'er on the ramps, but that's not the idea. Just to pass the visual spot check that I think the police will soon start to get quite hot on with the new MOT laws

[0rang3peel]

It's a stupid idea, because as said above the police or vosa don't dismantle your car at the side of the road.

You can just say the cat is located in the manifold.

[Carl-h]

I was reading into exhausts the other day saying that basically removing the cat and replacing with a straight through pipe is a bad idea for performance due to back pressure and pressure waves or something. Each cat is where it is on purpose to help the engine work. When they produce an exhaust they put a fake cat where the real one should be for power purposes. Apparently looks like a cat and helps performance so might be worth a look into?

I just keep my cat in, mainly because manifolds for mk2 VTR's are so expensive.

[Mochachino]

I still think its a viable idea. A fake Cat isn't going to fool an MOT'er on the ramps, but that's not the idea. Just to pass the visual spot check that I think the police will soon start to get quite hot on with the new MOT laws

It's a stupid idea, because as said above the police or vosa don't dismantle your car at the side of the road.

You can just say the cat is located in the manifold.

^^ as he said.

Also a fake cat will fool an MOT tester if it passes emissions, even if it dosent they will say the cat has had it, when you actually know its a dummy one. In some race sseries they leave the cat on and empty its insides to keep within the restrictions, do you think the MOT testers will take the car off and then have a look inside it?

[Mochachino]

I was reading into exhausts the other day saying that basically removing the cat and replacing with a straight through pipe is a bad idea for performance due to back pressure and pressure waves or something. Each cat is where it is on purpose to help the engine work. When they produce an exhaust they put a fake cat where the real one should be for power purposes. Apparently looks like a cat and helps performance so might be worth a look into?

I just keep my cat in, mainly because manifolds for mk2 VTR's are so expensive.

Not entirely. As in saying removing the cat on every engine will reduce its performance.

[MuZiZZle]

but this is for the MOT, what about before and after it?

[Carl-h]

Not entirely. As in saying removing the cat on every engine will reduce its performance.

Yes sorry I should of added, removing the cat even with a straight through pipe will still help, but you see more benefit from a false cat.

[Mochachino]

Yes sorry I should of added, removing the cat even with a straight through pipe will still help, but you see more benefit from a false cat.

Not necessarily. What works for one engine wont for another! So what you said may apply to 2 engines out of hundreds of different ones.

[Sexy_106]

So, as everyone knows after about 200 threads on the subject, the MOT laws have changed.

One of the changes mean you MUST have a catalytic converter in place, if your car came with one from the factory, whether or not it will pass an emissions test without one.

So, is anyone else considering fitting some kind of dummy cat incase of a road-side stop check? How would you go about it?

Obviously, you're not going to pass an emissions test with this in place - but if your car has been mapped for low emissions or you know a friendly MOT'er, a cat is just going to hold your performance back.

If you are that worried about visual checks then why don't you just leave the cat on your car?

[Sexy_106]

Not necessarily. What works for one engine wont for another! So what you said may apply to 2 engines out of hundreds of different ones.

+1.

Everyone's cars respond differently to different engine modifications.

[xscottxx]

If you're genuinely that worried about it why not just leave the cat on? I mean really, you're on the road anyway, do you need the extra performance?

[stupotvtr]

I have been driving for 4 years in modified cars and been pulled over in the double figures never once has the bonnet been lifted or under the car been checked.

They just check, tyres, screen wash, handbrake, lights, horn and anything that looks unsafe.

Grow a pair or leave the cat in.

[Skitts123]

I got pulled about 6 months ago for having a too loud exhaust! He checked over everything including in the engine bay, he took pictures of all of my mods.

[gazza808]

It's ironic really,
If cats weren't law companies could make super eco mega lean burn petrol engines. But because they have to map the engines in a way so not to melt the cat we don't get it.

Sent from my BlackBerry 9700 using Tapatalk

[JoshB]

I have been driving for 4 years in modified cars and been pulled over in the double figures never once has the bonnet been lifted or under the car been checked.

They just check, tyres, screen wash, handbrake, lights, horn and anything that looks unsafe.

Grow a pair or leave the cat in.

Where's your screen wash bottle?


If people are that bothered just weld a 200cell sports cat into a decat pipe. They're only about £70 and I doubt a 150bhp 1.6 engine is even going to notice its there.

[Cam]

Where's your screen wash bottle?




They ask to see it working just like they test on the MOT genius.

[JoshB]

They ask to see it working just like they test on the MOT genius.

I didn't ask for a cunts opinion.

[Prickle]

Leave the cat on. Its as simple as that.

Or buy a old car that doesnt have one from the factory.

[LSOfreak]

I was reading into exhausts the other day saying that basically removing the cat and replacing with a straight through pipe is a bad idea for performance due to back pressure and pressure waves or something. Each cat is where it is on purpose to help the engine work. When they produce an exhaust they put a fake cat where the real one should be for power purposes. Apparently looks like a cat and helps performance so might be worth a look into?

I just keep my cat in, mainly because manifolds for mk2 VTR's are so expensive.

not really, you get back pressure problems when the bore of the pipe is too big. The cat has some sort of honeycomb filter sort of thing inside it, so it restricts the system alot more than it being a staright pipe. Also the cat isnt put there on purpose to help the engine work. They only moved the cat to the manifold on cars because it gets warmer quicker, and being warmer does its job better.
All a dummy cat is, is usually a straight through pipe or silencer, with a bit of steel wrapped around to resemble a cat. They dont actually do anything. You might be getting confused with a sports cat, and they are very expensive and not really worth having imo, when a decat can be had for less than £30.

OP just lower your car all the way to the ground so they cant see it :D
ive never had a policeman check a cat, or emissions, and ive been pulled over for being too loud

[Jazz]

I've got de-cats on mine, its how I bought it. Being a 92 import I think the emissions requirements are slightly different, I'm not sure.

Either way I won't be catting up, even in the face of these changes. And I'll still pass.

[citroen_saxo_vtr]

I still think its a viable idea. A fake Cat isn't going to fool an MOT'er on the ramps, but that's not the idea. Just to pass the visual spot check that I think the police will soon start to get quite hot on with the new MOT laws

Do you not think the police would get wise to a fake cats? it would then be more of a reason for them to rip your car apart and find other illegal stuff. And the way to go around it is to get the 106 diesel centre pipe if you have an under floor cat job done as its got a box in were your cat should be.

[Tontsy]

just get a car PRE 1960 and you dont need an MOT.
or a tractor, they dont need them either.

and vosa can, and will just take your car there and then if they want too. so, if you think you will be fine by saying "ere ma silencer iz a kat innit" they arent retards like the clear majority of this site . . .

but yeah, i see no idea why it wouldnt work...just saying its not 100% if they have doubt.

[manta]

Easily sorted, just lop the cat off your old system, hollow it out and slide it over the new exhaust and weld in place.

[tillygti6]

for reference a non cat'ed jp4 motor with the usual mods actually produces under half the emissions that a pre cat car can and still pass.
i dont need a cat but as said a basic sport cat is perfect.

[Mochachino]

just get a car PRE 1960 and you dont need an MOT.
or a tractor, they dont need them either.

and vosa can, and will just take your car there and then if they want too. so, if you think you will be fine by saying "ere ma silencer iz a kat innit" they arent retards like the clear majority of this site . . .

but yeah, i see no idea why it wouldnt work...just saying its not 100% if they have doubt.

:S hmm

[tom130691]

its simple

apposed to de-cating your car open the cat take all the shit out then weld it back up

[kennym1987]

I've got de-cats on mine, its how I bought it. Being a 92 import I think the emissions requirements are slightly different, I'm not sure.

Either way I won't be catting up, even in the face of these changes. And I'll still pass.

if its an early 92 it wouldn't need a cat anyway as they became compulsary in august 92 when the law changed

[b0t13]

Btw its VOSA checks people need to worry about, not general police..

if you want to goto the effort of a fake cat for these checks then go for it, but it could still fail emissions anyway when tested at roadside,

if its the police, just bullshit the silencer if asked..

[devilsadvocate]

There is no such thing as a fake cat....it's either a cat or it's not.

[Gordi]

http://i6.photobucket.com/albums/y218/fezza_16v/cat.jpg

[Greedo]

Cheers for all the comments guys and girls. And fuck you too all the wankers that think they're clever with the stupid comments. :y:

My car has a custom aftermarket system on it at the moment, so leaving the cat in place isn't an option - it doesn't have one!

I can get through MOT's fine, but afew friends of mine in the force have mentioned that they've been advised to start checking things like the presence of a cat etc when the new MOT's come into play.

So for this reason, I'm considering welding an emptied cat in place over my exhaust - it will fool any visual police inspection, but obviously won't fool a VOSA emissions check

[Jaygovtr]

my mot's coming up and i dont have a cat im hoping for a dodgy mot lol

[yorkie]

get a old cat smach the middle out of it...... and the police have a mirror on a stick to look for cats lol fake cat winning!!

[jw1325]

I have been driving for 4 years in modified cars and been pulled over in the double figures never once has the bonnet been lifted or under the car been checked.

They just check, tyres, screen wash, handbrake, lights, horn and anything that looks unsafe.

Grow a pair or leave the cat in.

remember though... we live somewhere where the modified car scene is respected by our police force in return for the respect we give them. Ok, maybe not the normal Panda division but they lot don't know their arse from their elbows and hand out asbos like they're fucking sweeties, but the traffic division are more than leineint through here, and as long as all your essentials are in working order, they will turn a blind eye to the odd modification, most naughty plates etc. they won't go ripping cars apart, like some other police forces do.

[es_shoes_rock]

does someone still sell a "dummy cat" ? just fit one of them and say its a sports cat if you have any issues :)

[Ryan]

not really, you get back pressure problems when the bore of the pipe is too big. The cat has some sort of honeycomb filter sort of thing inside it, so it restricts the system alot more than it being a staright pipe. Also the cat isnt put there on purpose to help the engine work. They only moved the cat to the manifold on cars because it gets warmer quicker, and being warmer does its job better.
All a dummy cat is, is usually a straight through pipe or silencer, with a bit of steel wrapped around to resemble a cat. They dont actually do anything. You might be getting confused with a sports cat, and they are very expensive and not really worth having imo, when a decat can be had for less than £30.

OP just lower your car all the way to the ground so they cant see it :D
ive never had a policeman check a cat, or emissions, and ive been pulled over for being too loud


Read into pulse tuning.

[e8_pqck]

So many idiots.why flame the op? Sounds reasonable. He already sadhus he isn't trying to fool the mot tester and people already agree that they don't dismantle your car on the roadside. The first person to check is a Cooper and if he see something like no cat then he may call in vosa, but if he sees a lump in the exhaust where the cat is supposed to be he might leave it. He'll think you're an idiot if you tell him the cat is in the silencer!

[jamie281093]

sorry to bump..but was just reading through and i was thinking about decatting a while back, and a couple of days later i was parked up, had been a report against me apparently and police were looking at my car, and he did check underneath for a cat (he had trouble as it was lowered at the time lol), had it not been there and i said it was in the manifold im pretty sure he would have wanted to open the bonnet to have a look, most of them arent completely stupid, i wouldnt decat without a dummy cat, never ever ever :P

[wicked-vtr]

not really, you get back pressure problems when the bore of the pipe is too big. The cat has some sort of honeycomb filter sort of thing inside it, so it restricts the system alot more than it being a staright pipe. Also the cat isnt put there on purpose to help the engine work. They only moved the cat to the manifold on cars because it gets warmer quicker, and being warmer does its job better.
All a dummy cat is, is usually a straight through pipe or silencer, with a bit of steel wrapped around to resemble a cat. They dont actually do anything. You might be getting confused with a sports cat, and they are very expensive and not really worth having imo, when a decat can be had for less than £30.

OP just lower your car all the way to the ground so they cant see it :D
ive never had a policeman check a cat, or emissions, and ive been pulled over for being too loud

As Ryan said, this is incorrect.

The btb system I had on the saxo had a expansion chamber in the position of the cat, the pulse you get from a conventional engine ( e.g on a saxo 2 cylinders fire at a time) creates a resonance in the exhaust, when it reaches the expansion chamber it reverts back up the mani to the cylinder head. This resonance creates a temporary vaccume which draws the exhaust gas out of the combustion chamber more fully, leaving more room for fresh air/fuel.

This is how I understood it in my leymans mind, anyone who knows this is wrong or can explain it more fully feel free to chime in, a subject I'd like to hear more on.

[Manu]

keep your car legit or get a sports cat tbh. Can't stand the smell of unburnt petrol when I'm behind one of those noisy mothers.

[gazza808]

keep your car legit or get a sports cat tbh. Can't stand the smell of unburnt petrol when I'm behind one of those noisy mothers.

If your cars over fueling it'll still smell of petrol from behind cat or no cat...

[jamie281093]

If your cars over fueling it'll still smell of petrol from behind cat or no cat...

surley unburnt fuel would collect up in the cat too? safety hazard :panic:

[saxova]

surley unburnt fuel would collect up in the cat too? safety hazard :panic:

Cats work best at around 600'c. You think a little petrol there is dangerous? :P

Over-fueling damages cat's, No risk of explosions lmao.

[Oli-VTR]

my car failed its mot yesterday on emissions and not having a CAT. the bloke said emissions wise it was 0.2 to pass i got 0.25 so only just shy, but that under new rules i have to have the cat on to pass as well as the emissions being low enough. cars a mk2 vtr so im trying to source a mk1 underfloor cat as i cba with swapping the manifold!

[Oli-VTR]

ah forgot to say, my car has saxsport with the dummy cat in the centre section but he knew instantly it was a dummy and so still failed it

[Ross]

recommend you find a friendly MOT station tbh.

[KamRacing]

I guess you could have a fake lambda plugged in behind it to make it look legit...

[Manu]

If your cars over fueling it'll still smell of petrol from behind cat or no cat...

My car's fine, I'm only mentioning other chavved up bangers who are after the flame pop factor.

[LSOfreak]

recommend you find a friendly MOT station tbh.

this lol i dont know where i'd be without one

[danny-vts]

my mot on monday :(

top strut bearing is shagged
2 little holes on stainless centre box
snapped manicat/downpipe
engine management light is on.

ALL advisories :)

[jamie281093]

Cats work best at around 600'c. You think a little petrol there is dangerous? :P

Over-fueling damages cat's, No risk of explosions lmao.

I knew it wasnt good, just wasnt sure if you would get a bit of a bang or just like you said damages it, or something else, i wasnt sure :P

[AXracing]

As long as it passes gas test and no ECU light is on i think you may still be fine.

[KamRacing]

As Ryan said, this is incorrect.

The btb system I had on the saxo had a expansion chamber in the position of the cat, the pulse you get from a conventional engine ( e.g on a saxo 2 cylinders fire at a time) creates a resonance in the exhaust, when it reaches the expansion chamber it reverts back up the mani to the cylinder head. This resonance creates a temporary vaccume which draws the exhaust gas out of the combustion chamber more fully, leaving more room for fresh air/fuel.

This is how I understood it in my leymans mind, anyone who knows this is wrong or can explain it more fully feel free to chime in, a subject I'd like to hear more on.

Really the pulse tuning is all done by the manifold. I doubt theres a scavenging benefit to the small chamber, more likely its there for sound harmonics. The exhaust really is there to get rid of gases as quickly as possible and allow silencers to be fitted.

A cat is always going to be a restriction in the exhaust system. Its not good for power and acts as a bottleneck. Now what you have is an engine thats been mapped to get the best out of what is there so removing it can add a flat spot on some cars but theres generally a reasonable gain to be had.
Backpressure is not a good thing. People get confused as to what it is.
On a normally aspirated car you want gases to exit as fast as possible. Backpressure is an unwanted byproduct of fast gas speed so a balance is required. You tune the exhaust to give an optimum speed at a certain rev range. Go too big and gas speed drops, go too small and the engine is strangled at high revs. You then have to contend with bends and silencer design and other factors which is why there are often performance differences between systems.