BBR 200 NC1 Quick Queries

I have had my 2006 NC1 2.0 Sport for coming up to 3 years in spring and have absolutely loved it. A weekend car but I have also done 4 tracks days in it over the last 2 summers. The car is only worth £3/£3.5k but I am willing to spend that again to install the BBR 200 kit and the GT back box.

The car is fantastic in the corners but just needs that bit more acceleration and the 200 I feel is the perfect sweet spot for the money and will be spot on. A slightly more fruity exhaust note will be nice too.

There is an option for a cat manifold or one without. I think it was Matt from BBR I spoke to who said that both will pass the MOT. Is there any point in paying £200-£300 extra for the cat or is it worth it to 100% guarantee no emission fails come MOT time? What are the benefits/drawbacks of having/not having it?

My second question is what is the easiest way to declare the kit to insurance? A specialist like Adrian Flux will know what it is but I doubt Aviva will!


The question may be quick, but the answer isn’t :upside_down_face:

The official line (as far as MOTs are concerned) is that the car must have two cats because that is what it left the factory with.
In practice you usually get away with losing the front and retaining the centre one, rare someone will fail it for that, but it is a visual fail. With the OE entre one on it’ll still pass on emissions when warmed up.
The original cats are made to last the life of the vehicle, aftermarket ones are not. They’ll work for a while, but will cause a fail on emissions in time.

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Most of the cars I have modified before my MX-5 life have used “cat-back” systems, you delete the second cat keeping the one(s) nearer the engine. Never had a car fail the MOT with that arrangement, also never seen an MOT examiner look under the car, unless it fails the emissions so hopefully low chance of a visual fault. Can’t see it being a problem on the emissions front keeping the middle one as OP suggests.

[quote=“DuratecNC, post:2, topic:117717”]
The official line (as far as MOTs are concerned) is that the car must have two cats because that is what it left the factory with.
[/quoteGood morning.

Hmmm, This subject has cropped up again…
Mine has a 4-1 manifold and the standard CAT pipe in the middle and passes every year.
Now from the extensive research including posts on here I have not found what you say to be correct.
I have not found anyone that has had a car failed from this set up or indeed the other way around.
Likewise, I have searched the MOT testers manual and it doesn’t actually state that unless it has changed recently.
Also, you are NOT allowed to use prior knowledge when testing.
The big part is whether it passes the emissions.
Therefore, can you you provide the actual legislation that states that?

You’ve never seen an MOT tester look underneath a car? :rofl:

I have known fails for missing cats and it wasn’t on emissions. What I wrote is factual.
How you or the MOT tester apply it is another matter.

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I am not saying what you stated was non factual.
But can you provide the legislation that actually states that?
I have asked several people before this exact question and have never been provided with the evidence to substantiate the statement.
As stated, I have researched and not found that.(Unless I have missed a section some where).
I don’t wish to get into any arguments online either, merely having a debate.
If someone can prove that then fine. :+1:

“(a) Emission control equipment fitted by the manufacturer: missing, obviously modified or obviously defective” Major fail.


If it was fine and legal to remove cats then BBR would not have gone to the trouble of creating a replacement.
They put that on the market due to people complaining that their cars failed the test after one was removed.

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Interesting and thank you.
A can of worms indeed and interpretation as you said.

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Most testers may not go to the effort of peering past the upper heat shield from above or the engine tray from below to look for the presence of the factory catted manifold but it could easily become a requirement in future with any tightening of the regs. As stated elsewhere one cat will pass emissions wise but the life of that situation will also depend on how much richer mixture conditions on remapped cars affect the remaining cat.

It is and that’s before we start discussing the morals of too :stuck_out_tongue:


I agree, (ish). mk375
But as a tester you can’t apply prior knowledge to the test.(apparently).
My interpretation is that the legislation was written to stop people removing the cat/cat’s and by passing the emissions completely for various reasons.

“You only need to check components that are visible and identifiable, such as catalytic converters, oxygen sensors, and exhaust gas recirculation valves”.

As an example not all cars have a cat on the manifold, or even two of them.
So even looking you would see a header as normal and a cat in the centre.
The emission test is conducted and passes, so is that not what it’s all about really?
I am off for coffee now and hope the same chap passes mine in March! :wink:

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My BBR200 has no cat on the manifold and a sports cat in the mid pipe. It has passed emissions for the last 9 years. Presumably the testers didn’t count the cats.

The BBR conversion is great by the way. Not all that much more power, but just enough, and this coming from someone who’s previous MX5 had 400hp. Mine has Konis and BBR’s lowering springs and RX8 anti roll bars, which finish it off nicely.

Done 122,000 miles. Still uses no oil. Drives like new, except better in all the dynamics. Sounds good too.


Thanks all for your answers. Might still to go for the cat for added peace of mind but not booking in until the end of Feb so a while to make a decision.

The BBR 200 does seem ideal. I have Eibach 30mm springs and upgraded to steel lines, EBC discs, Yellowstuff pads and Michelin Pilot Sport tyres. Next to save up for after this is a proper suspension set up. Some would argue I should probably do that before power. Happy to hear views on this.

I recently got a Kia Stinger 3.3l V6 with 365bhp (fantastic car btw) so my MX5 is no longer my fast car haha. Handles brilliantly compared though which makes it all the better and much more fun. The Stinger is a brilliant GT cruiser with more kit than you can imagine. Only downside is how thirsty it is on fuel!

The only thing that worries me about the conversion is mine is the NC1 so the weaker engine and it does use a bit of oil but only when I’m hammering it all the time which could be normal when pushed. 100% no oil leaks but I’d cry if I spent all this money and then the engine shat itself! I’ve only done 86k miles so should have a long life ahead of it I would hope.

£2,700 drive in drive out for a low mileage 2.5 engine if your 2.0 carks itself. Plus remap.

You have hit the nail on the head.
They have to test it with what is presented and with no prior knowledge allowed.
“It would be impossible for a tester to know exactly what parts are fitted to the exhaust and emissions systems to every car on the road”.
So they see it has one. (Complies with the regulations).
They carry out the emissions test and it passes.
They issue the test certificate.
All testers can’t be incompetent.
I feel an enquiry coming on to DVSA.

They can take around 300whp so 200hp and a lot less torque than a 2.0 with a supercharger or turbo from the BBR should be totally fine. They are a pretty robust engine still, keep on top of the oil situation as driven hard they do seem to burn a tiny bit.

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Hi, I had mine done just over a year ago. I’m with Churchill insurance & the only thing they were interested in was the increase horse power figure which added about £30 to my annual cost.

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As promised I contacted DVSA with the enquiry.
This topic of people saying it’s an instant MOT failure if you remove the front Catalytic converter is just not correct.
It was and always has been my understanding that as long as the car meets current and the designed emissions standards for any car then you can delete either the front or centre Catalytic converters as in the MX5.
Likewise, you can modify the exhaust system as long as it complies with the noise (perhaps another topic)and the emissions.
People state BBR are correct is stating it will fail if you remove one.
That is not correct and in my opinion is a sales ploy, which is fine by me.
Please see my enquiry and the reply I have received.
I will also create another topic and post the information in due course.

I am wondering whether you can give me some help and advice on Catalytic Converters and Emissions for Spark Ignition Engines.
I have read sections in 8.2.1 as attached below, but to me and many others is a bit of a grey area.
Some cars have two catalytic converters and indeed some only one.

Those that have two fitted as an example may have one built into the manifold/header pipe and the other will be inline somewhere.

Some just have the two fitted inline within the system.

What I would like to know is what happens when a someone wishes to fit a complete road legal stainless steel exhaust system.


Removal of the front header and catalytic converter and be replaced by a standard after market 4-1 stainless steel manifold.

Replace the centre OEM catalytic converter and exhaust section (or keep just the catalytic converter) and replace with a new one and stainless exhaust sections to tail pipe including silencers etc…

In doing so this would fully meet or exceed the current emissions and therefore pass the test.

Now as you also know there are many “after market type approved items” on sale that can be fitted legally to vehicles and still pass the current emissions tests for cars.

Indeed they are recommended as direct replacements.

Quite a few companies can supply or indeed build them to specification.

Having read the below, to me it is slightly confusing because of the part about “Emission control equipment fitted by the manufacturer, missing, modified or obviously defective”.

So can you replace/modify the exhaust/emission control systems with aftermarket components so that it still controls and complies with the current emissions standards?

Am I correct in saying that this was written to stop people just deleting the emission control systems altogether?

Also, if say a catalytic converter should fail then a person could replace with an aftermarket one which fits into the category of not being fitted as standard and obviously modified.

BUT is type approved and legal as far as the emissions test goes.

The same logic can be applied to the complete exhaust system.

Likewise it would be impossible for a Tester to know or understand the complete exhaust/emissions systems on all road cars.

So am I correct in saying the tester would inspect for a Catalytic converter and conduct an emissions test in the normal way?

I look forward to hearing from you.
Kind regards,


Exhausts can be a problematic area in the MOT test. This is largely because the test is based upon the relevant legislation and this sometimes makes it difficult to assess compliance where modifications have been made or aftermarket components are fitted.

Firstly, it is illegal to replace or modify an exhaust so that it increases the noise made by the escape of exhaust gases (Road Vehicles Construction and Use Regulations 1986 -Regulation 54)

It is also illegal to make modifications to a vehicle that increases the levels of exhaust emissions (Road Vehicles Construction and Use Regulations 1986 -Regulation 61A). This is not just the emissions checked at MOT test, but all emissions that that must be met as part of the type approval process.

Therefore, if an aftermarket stainless steel exhaust is fitted, the MOT tester will need to assess that the exhaust noise is not unreasonably above the noise level you’d expect from a similar vehicle with a standard silencer in average condition. They would also check that no emissions control components are missing, obviously modified or obviously defective.

It is important to note that the regulations do not prevent modifications or the use of aftermarket components, including exhausts. The components are merely required to perform as well the OE components in respect of noise and emissions. If the design of the exhaust uses one catalyst where there were originally two, this is not necessarily an MOT failure, provided the system still meets the same standard for noise and emissions as the OE components did when in a serviceable condition. It may be necessary to show a receipt or other documentation to prove this, but like you say, most testers will not know how many catalysts were originally fitted.

In all cases, where there is doubt about whether a defect exists, testers should give the benefit of the doubt and pass the vehicle.

I hope this helps.
Best regards

Shaun Martin | Policy Specialist (MOT Testing Service)
Driver and Vehicle Standards Agency | Berkeley House, Croydon Street, Bristol BS5 0DA